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Volume 19

Issue 3 2006

Center for Photochemical Sciences

A Transient Lifetime in PhotochemistAn Interview with Anthony Trozzolo


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TheSpectrum Volume19Issue32006 Page

viewpoint

The interview with Tony Trozzolo in this issue is one that should have happened long beore this. Tonys role in develop-ing the photosciences as a separate area o research was cemented by his organizing the rst Gordon Conerence on OrganicPhotochemistry in 1964. When I saw the picture o the conerence attendees (page 5) again I was surprised by how ewpeople I recognized, how big the conerence was, and how slender we all were! (I am in row 5 rom the top. Nick Turro isin the top row.) More than hal the participants were rom industry. Who did not attend is almost as interesting as who did.None o the industrial scientists we know today as the giants o the fedgling areas o photoresists and photopolymeriza-tion attended the conerence. I didnt see Lou Minsk, Louis Plambeck, Rol Dessauer, Edwin Lamb, Leopold Hrner orChester Carlson on the attendance list.

Lasers were so new that I dont even remember seeing one until ater the conerence; none o the laser jocks o theday showed up. George Porter was there but barely mentioned fash photolysis as I remember, but Ronald Norrish, GntherSchenck, and Theo Frster were not. Each played major roles in research in the photosciences in England and Europe.

Nevertheless, there were many industrial attendees and or good reason. Many industries were exploring the use o thephotosciences in processes. And many other industries were exploring new opportunities that used photochemistry. I recallparticularly the large groups at the then Union Carbide in Tarrytown, NY, and Charleston, WV. Dave Trecker at UnionCarbide contributed a number o new photoinitiators. Dessauer, at DuPont, has already been mentioned. (The Spectrum,Vol. 16, Issue 4)

Industrial research has really gone down hill since the halcyon days o the 1960s. Very ew companies in the U.S., atleast, have anything resembling basic research labs. Bowling Green is near Toledo, OH, which was the original homeo many large industries in glass and automobile parts. These industries include Owens Illinois, Owens Corning, LibbeyOwens Ford, Champion Spark-plug and Dana Corporation. Each had corporate research eorts when I moved to the areain 1973. None have corporate research eorts now. Two have gone through bankruptcy. One has been taken private andback public. Another was purchased by rst an English, and later a Japanese glass rm. The other one evaporated. OwensIllinois, or example, has gone through a series o restructurings and sell-os. This month it was announced that they wereselling their plastics products division. Though the stock is going up, one wonders whati anythingthe company hasor sale.

Tony Trozzolo is ond o talking about that rst Gordon Conerence, and in discussing the many persons that attended it.The attendees came rom very dierent backgrounds. Photochemistry, particularly organic photochemistry, beneted romthe physical tools that were just coming to their laboratories like gas chromatography and emission spectroscopy. Physicalchemists and theoreticians, on the other hand, beneted rom having their explanations needed. The older, dyed in thewool, photochemists like Harry Gunning rom Calgary and Robert Livingston rom Minnesota delighted in all o the at-

tention the use o light in chemical reactions was receiving. Older physical organic chemists, like Saul Cohen, ound thephotosciences a way to invigorate their laboratories and provide them younger collaborators.

The photosciences, since those early days, have grown mature in some ways. That old Gordon Conerence has gottena little bit old itsel. But the spirit remains, and the excitement abounds every two years when the group o photoscientiststhat Tonys conerence begat, reacquaint or still another session in New Hampshire, Massachusetts or Rhode Island.


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an interview with Anthony Trozzolo

special feature

perspective ona transient lifetime in photochemistry

Anthony Trozzolo is recognized or outstanding contributions to the science o photochemistry.

The Gregory and Freda Halpern Award in Photochemistry o the New York Academy o Sciences

Page4 Volume19Issue32006 TheSpectru

CourtesyofAnthonyTrozzolo

will even learn why Trozzolos most requested talk on theAmerican Chemical Society (ACS) lecture circuit is a loto Bologna.

Tony Trozzolo is the Charles L. Huisking ProessorEmeritus o Chemistry at the University o Notre Dame.

He received his B.S. degree in chemistry rom the IllinoisInstitute o Technology in 1950 and the M.S. and Ph.D.degrees rom the University o Chicago in 1957 and 1960,respectively. In 1959, he became a Member o the TechnicalSta at the Bell Telephone Laboratories in Murray Hill,New Jersey, where he remained until 1975 when he becamethe rst Huisking Proessor at Notre Dame.

Trozzolos research has ocused on the creation and de-tection o reactive intermediates. The methodology oteninvolves low-temperature photochemistry or solid-statephotochemistry. Among the intermediates studied are car-benes, azomethine ylides (rom aziridines), carbonyl ylides(rom oxiranes), and nitrenes (rom azides). The detectiontechniques include e.p.r. spectroscopy, laser spectroscopy,and optical spectroscopy. Trozzolo also has conducted re-search in the ollowing elds: photostabilization o poly-mers, dye lasers, singlet molecular oxygen, charge-transercomplexes, molecular magnets, and superconducting inter-calation complexes.

That work resulted in more than 90 research articles and31 U.S. and oreign patents. Noted as a dynamic lecturer,Tony has delivered over 300 invited lectures at universities,international meetings, ACS symposia, and industrial labo-ratories. His numerous awards and honors (www.nd.edu/~atrozzol/) include two perhaps unique among photochemi-

cal scientists. In 1997, Tony was named Honorary Citizeno Castrolibero, Italy, and selected as the rst recipient othe Pietro Bucci Prize co-sponsored by the Italian ChemicalSociety and the University o Calabria. He was also theourth awardee (ater Nick Turro, Orville Chapman, andHoward Zimmerman) o the Gregory and Freda HalpernAward in Photochemistry o the New York Academy oSciences in 1980.

The Spectrum: What led you to organize that

rst Gordon Research Conerence on Organic

The late Thomas Kuhn, authoro that 1962 classic in the phi-losophy o science, The Structureo Scientifc Revolutions, arguedthat science does not advance

through a linear accumulation onew knowledge. Instead, it under-goes periodic revolutionspara-digm shits, he called themthatabruptly transorm scientic in-quiry within a particular eld.

What osters these shits? Many o us have been eyewit-nesses to one example. It was the late Richard E. Smalleysskillul use o the orum provided by a Nobel Prize (http://pubs.acs.org/cen/coverstory/84/8441cover.html) to shep-heard emergence o nanoscience and nanotechnology as anew scientic discipline. A seminal conerence or landmarklecture also may help oster the consolidation o an emerg-ing eld o science.

The rst Gordon Research Conerence on OrganicPhotochemistry had such an eect, according to some pio-neers in this now-robust eld. They regard that 1964 con-erence as the seminal event in organic photochemistrysemergence as a sel-standing discipline in chemistry. TheSpectrumis delighted or the opportunity to chat in this edi-tion with the individual who organized and chaired that rstconerence and played such a memorable role in the matu-ration o organic photochemistry.

In this interview, however, Anthony M. Trozzolo identi-es an earlier conerence as the seminal event in organic

photochemistrys emergence. Trozzolos pick is an ACS or-ganic chemistry symposium at Indiana University in whichHoward Zimmerman and George Hammond galvanized at-tendees with interpretations or a variety o organic photo-transormations.

Neither o those giants in the eld was present at therst Gordon Conerence. Trozzolo explains the reason,discusses how photochemistry and its practitioners havechanged over the years, describes the evolution o his ownresearch, and oers insights and advice or younger scientistsand scientists acing decisions about retirement. Readers


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Anthony M. Trozzolo


Photochemistry in 1964? Take us back to the early1960s and describe what was happening in the lab andthe marketplace to create the need or such a conerence.

Trozzolo: In 1962,Proessor W. GeorgeParks, the Director othe Gordon ResearchConerences, publisheda notice in Science solic-iting proposals or newGordon Conerences.I sent in a proposal cit-

ing the act there was noconerence being heldon a continuing basis onorganic photochemis-try and that the subjectwas developing at a veryrapid rate. Althoughthe proposal was notacted upon in 1962, achance meeting at aluncheon (1963 MetroRegional Meeting inNewark) with Cecil L.Brown, who was on the Board o Trustees o the GordonConerences, gave me the opportunity to reinorce the caseor a conerence, and the Gordon Conerence on OrganicPhotochemistry was approved to be held or the rst time in1964 at Tilton School in New Hampshire. Coincidentally,an International Conerence on Photochemistry (honoringW. A. Noyes) was held in Rochester in March 1963 and I hadthe opportunity to meet many o the leading photochem-ists, such as Ronald Norrish, George Porter, Albert Weller,Egbert Havinga, Gunther Schenck and others. Attendanceat this meeting proved invaluable in contacting prospectivespeakers or the Gordon Conerence.

The Spectrum: So you assembled the leaders in the eld.Who was there?

Trozzolo: Since this was the rst Gordon Conerence onOrganic Photochemistry, I had the luxury o choosingspeakers rom the entire eld since no one had spoken be-ore. In 1963, photochemistry studies were largely ocusedon the use o energy transer in controlling the excited-statechemistry although charge-transer quenching was beingstudied by Albert Weller and others. The program o the

rst Gordon Research Conerence was arranged to show thisprogression. The rst speakersGeorge Porter and N. C.Yangstressed energy transer and dierences in reactivityo singlet and triplet excited states while the Friday speak-

ersSean McGlynn andAlbert Wellerconcen-trated on charge-transerprocesses. Other speakersincluded Orville Chapman,Gary Grin, RudolWolgast (pinch-hitting orGunther Schenck), HarryGunning, James McNesby,

Ted Ullman, RobertLivingston, Ed Wasserman,and R. Srinivasan. Withthis core o thirteen speak-ers, we had plenty o timeor short contributed talksand inormal discussion.

The Spectrum: How

many were in attendance?

Trozzolo: There were 120conerees, 73 o whom came

rom 42 dierent industrial labs (How times have changed!).Included in the 36 academic conerees (nine o whom werespeakers), were three young postdocs rom Harvard aboutto launch brilliant academic careers who drove together tothe Conerence rom Cambridge, namely, Nick Turro, DougNeckers and Jacques Streith. In later years when I served onthe Screening and Scheduling Committee and the Boardo Trustees o the Gordon Research Conerences, I alwaysadvocated the inclusion o postdocs and even graduate stu-dents as participants in the Conerences. Paul Kropp andthe late Don Arnold were in industrial labs in 1964, but lat-er, both became academicians and both served as Chairman

o the Conerence in subsequent years. Other young acade-micians in attendance included David Hercules, Sally andFrank Mallory, Al Padwa, David Schuster, Peter Borrell,Peter Leermakers, Tony Testa, Colin Steel, and Ron Sauers.In addition to Ed Wasserman, Bell Labs colleagues (who allhave played a role in the development o photochemistry)at the Conerence included Ed Chandross, Adam Heller,and Larry Snyder.

The Spectrum: What did they discuss, what ideas

emerged, what do you recall most about the sessions?

Groupphotoofthe1964GordonConferenceonOrganicPhotochemistry.

CourtesyofGordonResearchConferences


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Anthony M. Trozzolo


Trozzolo: The topics in the invited talks included: pho-tochemistry o carbonyl compounds, photoisomerizations,photochromism, photolysis o hydrocarbons, epr o tripletground-state molecules, photoreactions o olens catalyzedby pi-complexes, charge-transer in excited states, photo-cleavage o episuldes, and quenching mechanisms (elec-tron transer vs. energy transer). The discussion periodsalways seemed to go overtime. This was a time or us to getto know each other and to nd out what other interestingsystems were being studied and what mechanistic conceptswere being applied or in need o renement. My guess is thatthe impact o the conerence was really elt only ater wereturned to our respective institutions and had time to savor

what had transpired in the week at Tilton School.

The Spectrum: Some o the attendees look back on this

conerence and say that it was the seminal event thatsolidied organic photochemistry as a sel-standing eld

in chemistry. Was it the conerence content, or the actthat organic photochemistry had reached the point where

a Gordon Conerence was warranted, or both or what?

Trozzolo: I am happy to hear that some attendees eelthat it was a seminal event, but or me another event tookplace in 1961 which urther increased our interest in pho-tochemistry and its implications in mechanistic organicchemistry. The 19th Organic Chemistry Symposium tookplace at Indiana University and two o the speakers, HowardZimmerman and George Hammond, presented their respec-tive studies and interpretations or a variety o organic pho-totransormations. It was evident that mechanistic organic

photochemistry was becoming more rational and excited-state descriptions (largely obtained rom the detailed studieso spectroscopists) could be used along with the concept oenergy transer (rom photosensitization studies) to explainmany photochemical reactions. We had reached a pointwhere it was clear that enough was going on in the eld ophotochemistry to warrant bringing together that commu-nity and the Gordon Conerence structure with its great op-portunity or inormal discussion seemed a natural solution.Proessor W. George Parks Science ad mentioned earlier pro-vided the incentive to ollow the third line in Rabbi Hillelsdictum: I not now, when?

The Spectrum: Those attendees still remember GeorgePorters talk. By one account, Porter barely mentioned

fash photolysis or which he would win the Nobel Prizea ew years later. What do you recall about George

Porters presentation and about George himsel?

Trozzolo: Porters talk was mainly about the reactivity oexcited states o carbonyl compounds and the electronictransitions which created these as well as the dierences inreactivity o the singlet and triplet states produced. He hada mechanical model which illustrated the transition and themovement o the electron changing its orbital location. As Imentioned earlier, I had met George Porter on two occasionsin 1963, in March at the Noyes Symposium in Rochester,and in July at the 6th International Symposium on FreeRadicals held at Cambridge, England. As a pioneer in thetechnique o matrix-isolation, he was particularly interestedin our use o the technique at Bell Labs done in collabora-tion with Ed Wasserman, Bob Murray, Gerry Smolinsky, andBill Yager in which the triplet ground-state structure o avariety o carbenes and nitrenes had been determined. I waspleased to learn in early 1964, that he would not only beable to speak at the Conerence, but that he was bringing hiswie, Stella, and their two young sons, John and Andrew.

The Spectrum: Were children allowed on site in thosedays?

Trozzolo: At that time, Gordon Conerence regulations pre-vented children under the age o twelve rom being housedat the Conerence site, and so we arranged or the amily tostay at Webster Lodge on Webster Lake just a ew miles awayrom Tilton School. Porter later wrote that it was a greattime or the amily. In 1967, George and I were both sched-uled to present plenary lectures at the 8th InternationalSymposium on Free Radicals in Akademgorodok, Siberia. I

GeorgePorterandNickTurroatthe1994IUPACSymposium

onPhotochemistryinPraguewhenNickreceivedthePorter

Medal.



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Anthony M. Trozzolo


was looking orward to seeing him there, because one o hisgraduate students, Willie Gibbons, had come to Bell Labsto help me elucidate the electronic spectra o aryl carbenes,and we had ound a great similarity between our spectra andthe spectra o the benzyl radicals which Porter had producedby fash photolysis. Unortunately, illness kept him rom at-tending. We met periodically at IUPAC symposia, and in1986, the University o Notre Dame awarded him an honor-ary Doctor o Science degree.

The Spectrum: Was there any sense that George washeaded or a Nobel Prize?

Trozzolo: In 1964, it was clear that matrix-isolation tech-niques had permitted the characterization o reactive in-termediates by stopping them dead in their tracks andallowing spectroscopic measurements. Porter and Norrish,in developing fash photolysis, made it possible to generatea large population o the reactive intermediate over a veryshort time, and thus do spectroscopic measurements on theunencumbered intermediates. It became evident that thiswould be part o the wave o the uture as lasers becameavailable and in 1967, the Fith Nobel Symposium on FastReactions and Primary Processes in Chemical Kinetics washeld in Sweden eaturing Manred Eigen, Ronald Norrish,and George Porter. The three shared the Nobel Prize inChemistry that December.

The Spectrum: Why were George Hammond and

Howard Zimmerman missing rom that rst conerence?

Trozzolo: One o the rst persons that I invited to lectureat that rst Gordon Conerence was George Hammond.However, just shortly beore that time, George had suereda ainting spell at the 1963 all ACS meeting in New Yorkand or health reasons did not eel that he could accept.However, he did like the idea o a conerence on photochem-istry, and having an international perspective, became the

organizer o the rst IUPAC Symposium on Photochemistrywhich was held in Strasbourg in 1964. These two series oconerences, along with the International Conerence onPhotochemistry (organized mainly by physical chemists)and, more recently, the I-APS Conerences, have provid-ed the main orums or the photochemist. I also invitedHoward, but George Hammond had invited him to theIUPAC Symposium. My recollection is that Howard alsowas going to spend some time in Europe visiting riends andormer colleagues, thereby conficting with GRC. I shouldhasten to add that both George and Howard attended the

second Gordon Conerence (chaired by the late OrvilleChapman) in 1965, and Howard has attended most o theConerences since 1965.

The Spectrum:So youve attended every GordonPhotochemistry Conerence since then?

Trozzolo: No, I missed the 1967 and 1975 Conerences. In1967, I was invited to present a plenary lecture at the 8thInternational Symposium on Free Radicals which was be-ing held in Akademgorodok (near Novosibirsk) in Siberiaat the same time as the Gordon Conerence. It was a greatopportunity to visit the Science City that I had heard so

much about as well as scientists in Moscow and Leningrad.In act, due to the political situation at that time, it tookabout three months beore I got approval to go rom BellLabs. I missed the 1975 Conerence because our move toNotre Dame coincided with the date o the Conerence.The 1975 Conerence was the last held at Tilton School, aswe were moved to the more rustic environment o ProctorAcademy or the next eight conerences.

The Spectrum: What changes have you noticed inthe participants, their presentations, their outlooksas photochemistry matured as a science and younger

scientists entered the eld?

Pastchairsandfuturechairinattendanceatthe2005Gordon

ConferenceonPhotochemistry.Standing(left-to-right):GarySchuster(1989),PaulKropp(1971),LarenTolbert(2003),

LindaJohnston(2007),DavidWhitten(1997),andTrozzolo

(1964).Seated:RichGivens(2001),V.Ramamurthy(2005),

KirkSchanze(2005),andNickTurro(1973).

CourtesyofDollyTrozzolo


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Anthony M. Trozzolo


Trozzolo: There have been a number o major changes inthe Conerence since 1964. The biggest change has beenthe large decrease in industrial conerees so that the last ewconerences have only had a handul o industrial partici-pants as compared with 73 at the original Conerence. Thesize o the Conerence peaked in 1981 with 145 conereeswith the last ew conerences averaging slightly above 100.The other major changes, which I consider positives, havebeen: (1) greater number o oreign conerees (~40%) giv-ing the Conerence an international character; (2) greaternumber o women (The chair o the 2007 Conerence isLinda Johnston); and (3) the greater participation by post-docs and graduate students.

With the increased activity in the eld o photochemis-try, the program has also changed so that rom the 13 invit-ed speakers in 1964, we had 34 invited speakers at the 2005conerence, which, in addition, had two poster sessions(posters were not permitted in 1964). The 2005 Conerencehad a relatively large number o graduate students and post-docs, who as rst-time attendees obviously enjoyed the in-ormal interacton with an international group o their peersand armed the vitality o the subject. Everyone seemedto participate in the discussions, whether in the lectures orthe poster sessions. It is particularly satisying to me to seethe younger scientists o earlier conerences progress in theircareers and contribute to the eld as photochemistry inter-acts increasingly with other areas such as materials research,nanotechnology, photobiology, and renewable energy.

The Spectrum:You have the reputation as a dynamic,compelling lecturer. Doug Neckers remembers one o

your lecturesat the University o Kansas when youwere with Bell Labsdespite the passing o almost 40years. It dealt with azo compound isomerizations. What

are the secrets to leaving that kind o impression? Whatadvice can you oer students and younger scientists

about delivering an eective talk?

Trozzolo: Im fattered that Doug remembers. Actually, theseminar that Doug reerred to was in 1963, when he wasa graduate student at Kansas and his advisor, Earl Huyser,invited me to give a talk on our recent results on photo-decompositions o bis-diazo compounds which producedi-carbenes and intermediates with interesting structures(Since Earl and I both had Wilbert Bill Urry as our gradu-ate advisor at the University o Chicago, I can claim Dougas a scholastic nephew). How does one give a memorablelecture? I believe that there are several eatures involved.Since the primary purpose o the lecture is to communicate,

it ollows that the most important ingredient is content; inother words, have something to say, a story to tell. I haveseen talks which were beautiul powerpoint presentationsbut had little content, and one comes away disappointed.

The second ingredient is to be enthusiastic about hav-ing the opportunity to relate your story, particularly whenit involves novel and unexpected results. It is also impor-tant that you introduce the subject o the talk in a mannerin which you and the audience have the same universe odiscourse. Oten it is possible to present a talk as a de-tective story with its mystery or unsolved problem; themethodology is introduced, there are a ew unexpectedturns, and the mystery is solved. Equally important is the

eective use o visual aids, whether blackboard, slides, or

demonstrations. Ever since my teens, magic has contin-ued to be one o my hobbies, and I believe that perorm-ing magic tricks can make you a better lecturer. In one omy lectures on photochromic substances, I produce a posterwhich appears to be blank. When a black light is passedover the poster, the message Its not magic, its photochem-istry suddenly appears. Its also the message o Hammond

and Zimmerman at the 1961 Organic Symposium and thato the rst Gordon Conerence in 1964.

The Spectrum: What rst sparked your interest inscience during childhood? When did it happen? Were

there mentors or role models in elementary school orhigh school, or instance?

Trozzolo: My interest in science probably began in the late1930s when the Museum o Science and Industry openedits west wing. My older brother, Mario, and I spent many

Panelistsinaseminar,OriginsofPhotochemistryinItaly,heldApril1993attheCasaItalianaatColumbiaUniversity.

Left-to-right:HeinzRoth,MaristellaLorch(DirectoroftheCasa

Italiana),AngeloLamola,NickTurro,andTrozzolo.



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Saturdays visiting the museums o Chicago and what weound particularly appealing about the Museum o Scienceand Industry (it also was called the Rosenwald Museum)was the hands-on exhibits. I liked the colors produced bypolarizing lters and wondered how the color was created.There was a Fire Show each October which illustratedvarious orms o combustion, and an exhibit on the hydro-lysis o water. I was attracted to chemistry because o its sen-sual eects such as color changes, white precipitates, crystalso various shapes, etc. Although most o my teachers in bothelementary and high school were very dedicated (their earlycareers began in the Great Depression), several stand out.

My second grade teacher, Miss Margaret Oliphant, taught

me the values o good penmanship, neatness, and responsi-bility. She also double-promoted me into the advanced halo third grade. In high school, I had Mrs. Anatasia Springeror most o my math courses. In addition to being a greatteacher o mathematics, she was the aculty sponsor o theSlide Rule and Math Club and when the Club met aterschool hours, she personally helped me to empirically de-rive by induction the ormulas or permutations and com-binations. My Italian teacher, Mrs. Antenisca Nardi, whoalso had taught my older brothers, strongly encouraged usto continue our education in college, and even visited myparents to stress this point. My chemistry teacher, FrancisC. Coulson, reinorced my interest in chemistry. He said (injest, I assume): Stay in chemistry, and youll win a NobelPrize.

The Spectrum: Well, maybe you came closer than youknow.

Trozzolo: The closest that I came to ullling that prophesywas when Doug Neckers, my wie and I were in the audienceat the Award Ceremony to see Roald Homann and the lateKenichi Fukui receive their Nobel Prize in 1981, but werestill waiting or the phone call rom Stockholm.

The Spectrum: Did you conduct research as anundergraduate?

Trozzolo: My undergraduate research advisor at IllinoisTech, Eugene Lieber, provided me with the opportunity topresent our results at the September 1949 ACS Meeting inAtlantic City under the title The Hydroxylamine NumberApplication to the Identication o Ketones. He was alsothe one who introduced me to the methodology o doing re-search. That research also led to my rst publication in theJune 1950 issue oAnalytical Chemistry. At the University o

Chicago, my advisor, Wilbert H. Urry, convinced me to goback to graduate school in 1956 (even though I was marriedand had a son) and provided a Union Carbide Fellowshipwhich was specically given to married students.

At this point, I think that its important to acknowl-edge the nancial aid which was provided to me both inthe orm o undergraduate scholarships and Atomic EnergyCommission and National Science Foundation GraduateFellowships as well as the aorementioned Union CarbideFellowship. Without those sources o support it would havebeen dicult i not impossible to pursue my studies and re-search. The presence o role models continued at Bell Labsas we kiddingly reerred to our in-house collaborations as

being each others postdoc. These collaborations widenedgreatly our research horizons.

The Spectrum: Tell us about how you ound your way to

Bell Labs and then to Notre Dame.

Trozzolo: My interest in photochemistry actually began asan interest in the spectroscopy o charge-transer complexesduring the three years (1953-56) that I spent at ArmourResearch Foundation (now IIT Research Institute) workingon a variety o contract research projects. I had always hada ascination or generating colors by chemical reactionsand the mere mixing o trinitrobenzene and anthracene insolution to generate an orange color provided an excellentexample worthy o explanation. The classic Mulliken paperson charge-transer had just appeared and stimulated manystudies in this particular area o research. My interest insolid-state organic chemistry also began during this periodunder the tutelage o the late Walter McCrone, who wasalready at that time a microscopist o international repute.

When I returned to the University o Chicago in 1956 topursue my doctoral research with Proessor Wilbert H. Urry,my studies initially concentrated on the photochemical de-composition o diazomethane in polyhalomethanes (a reac-tion which has had very interesting mechanistic aspects),

but ultimately became concerned with bimolecular initia-tion o ree-radical reactions. It was near the end o this pe-riod (1958) that I became aware that Bell Laboratories wasgoing to add a ew organic chemists to its technical sta inMurray Hill. I was ortunate enough to be one o the veadditions in 1959 to join Ed Wasserman (who had arriveda ew years earlier rom Harvard) in the department headedby Field H. Winslow.

The years that ollowed were to be scientically reward-ing or each o the six (Ed Chandross, Gerry Smolinsky,Dick (Paul) Story, Bob Murray, Ed Wasserman and me),


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and later, Heinz Roth, as we launched our individual ca-reers in physical organic chemistry, and in particular, thecreation, detection, and characterization o reactive inter-mediates, such as carbenes, carbocations, and nitrenes. Inmany o these studies, the photochemical decomposition oa suitable precursor was the preerred method or generat-ing the reactive intermediate. Also, I would be remiss i Idid not acknowledge the encouragement o the Bell Labsadministration, particularly that o our department head,Field Stretch Winslow, a pioneer in polymer chemistry,who became the ounding Editor oMacromolecules in 1968.Stretch celebrated his 90th birthday last June.

The Spectrum: And your path to South Bend, Indiana?

Trozzolo: The path to Notre Dame probably began (al-though I didnt realize it at the time) in 1971 when NickTurro invited Angelo Lamola and me to give his photo-chemistry course at Columbia since he was going to be on

leave (as it turned out, although he was on leave, he stayedat Columbia during this period). It was my rst teaching ex-perience since my undergraduate days at Illinois Tech (I hadbeen an AEC and NSF Fellow at Chicago, and these el-lowships carried no teaching responsibilities) and I enjoyedit very much except on two occasions. The rst exceptionwas when I had to lecture on carbonyl photochemistry withNick Turro in the ront row (he came to all the lectures)and the second was when I had to give a magic show withKoji Nakanishi in the audience. Talk about carrying coalsto Newcastle!

In the ollowing year, I was invited to give a series o PeterC. Reilly Lectures at the University o Notre Dame. Thetitle o the series was Creation and Detection o Excited-State Intermediates and the lectures dealt with photochro-mism, singlet oxygen, and dye lasers. Although I had beenraised in nearby Chicago and did not leave until the com-pletion o my doctoral research, and had been a lie-longNotre Dame ootball an, I had never visited the Universitybeore my lectures in October 1972. In 1974, I was oeredthe Huisking Proessorship in Chemistry at Notre Dame anda year later in 1975, I joined the Department o Chemistryand became a member o the Radiation Research Laboratoryas well. It was not easy to leave Bell Labs superb research

environment and my colleagues there, many o whom hadinternational reputations as outstanding researchers, but inretrospect, it was the right thing to do at that time.

The Spectrum: What kept you at Notre Dame?

Trozzolo: Even beore I arrived at Notre Dame, my careerbegan to take on additional acets, involving more admin-istrative unctions, such as the Associate Editorship o the

Journal o the American Chemical Society and the EditorshipoChemical Reviews (One can point out that the last threeEditors oChemical Reviews, Harold Hart, mysel, and thecurrent Editor, Jose Michl, have all had photochemicalresearch interests) and many committee and Board as-signments both in the ACS and in the Gordon ResearchConerences. Also, being the early occupant o an endowedchair at Notre Dame made me vulnerable to requent as-signments on various committees such as search commit-tees or additional chair positions which were then beingestablished. While these assignments were time-consuming,I elt that I was participating actively in the development othe University.

In addition, the presence o many congenial colleagues,both in the Department and throughout the University, andmany excellent students has made the last thirty-one years

quite intellectually satisying and six Notre Dame degreesor my children attest to the nonscientic gratication en-joyed during this period. When our children were under-graduates at Notre Dame, I would oten be pleasantly sur-prised by encountering them on campus on their way to aclass (They all lived on campus even though our home wasthree miles away). But the main reason or remaining is thesame as the reason that I came, namely, that as KingmanBrewster, then president o Yale, said in his preace to FatherTheodore Hesburghs book The Humane Imperative: Yet be-cause o the religious heritage o the place, Notre Dame is one

Field(Stretch)Winslows80thbirthdayin1996.Left-to-right:

Trozzolo,Stretch,EdChandross,EdWasserman,andGerry

Smolinsky.


Anthony M. Trozzolo



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o the ew universities I know that reminds the visitor, as well asthose who work and study there, that learning at heart is a mor-

ally motivated act.

The Spectrum: How did your research interests changeover the years?

Trozzolo: My undergraduate research at IIT involved us-ing the oximation o ketones as an quantitative analyticaltechnique or their identication. At Armour ResearchFoundation I became interested in microscopic techniquesor studying a variety o organic solid-state problems, in-cluding charge-transer complexes. My doctoral research

involved thermal bimolecular initiation o ree radical reac-tions. At Bell Labs, the general theme became the creationand detection o reactive intermediates such as carbenes,

dicarbenes, ground-state triplet and quintet species, singletmolecular oxygen. The creation step usually involved thephotolysis o a suitable precursor, and the detection and

characterization usually involved a spectroscopic techniquesuch as electron spin resonance, absorption or emissionspectroscopy, chemically induced-dynamic nuclear polar-ization (CIDNP). I also became interested in the oxidativephotodegradation o polymers which led to some interestingexcursions into photobiology in collaboration with AngeloLamola and Susan Fahrenholtz.

Another collaboration with Hollis Wickman led (seren-dipitously) to the synthesis and characterization o the rstmolecular magnet, the pentacoordinate bis-(N,N-diethyldithiocarbamato)iron III chloride, which, in addition to itsnovel magnetic property, had a spin quartet ground state.Collaboration with Chuck Shank and Andrew Dienes led

to the exciplex laser with very wide tunability range in thevisible based on simple notion o dierences in pKa betweenground state and excited state o hydroxy-coumarin dyes.One o the interesting eatures o these studies was that onecould time-resolve the stimulated emission rom the variousexcited states and thus get a time-prole o the excited-stateproton transers.

The Spectrum: Some o your work was in

photochromism?

Trozzolo: Our interest in photochromism actually was thespin-o o a collaboration with the late Gary Grin whowas interested in the photolysis o oxiranes as a source ocarbenes. Low-temperature studies showed that a coloredintermediate was being ormed in addition to the carbene.It turned out to be the carbonyl ylide.

By turning our attention to aziridines, Thap DoMinh andI were able to generate colored azomethine ylides, whichwere stable at room temperature or many hours. Theseturned out to provide or some very useul lecture demon-strations o the ability to control lietimes o the coloredspecies (azomethine ylide) by making use o substituents,solid-state environment, and, o course, orbital-symmetryconservation rules. At Notre Dame, Tom Leslie was able

to get fuid solution lietimes o the ylides by laser kineticspectroscopy. Some recent interest has been in the nonlin-ear optical properties o the photochromic aziridines. Alongthe way, I managed to do some applied research, usually asthe outgrowth o other studies, so that patents have beenissued in the area o dye lasers, photochromic lenses, andcopper deactivators (to stabilize polyethylene against auto-oxidation).

The Spectrum: How did you become Huisking Proessor

o Chemistry?

Anthony M. Trozzolo

ExciplexdyelaserdevelopedwithCharlesV.ShankandAndrew

DienesofBellLabsin1970.Chuckischangingthewavelength

andAndrewischangingthespatialdistribution,allhappening

duringthephotographexposuretime.

CourtesyofBellLabs



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Trozzolo: When I was rst contacted about a position atNotre Dame in 1974, I did not know that it was about anendowed chair. My visit as Reilly Lecturer in 1972 had leta very avorable impression about the hopes and aspirationso the Department o Chemistry. Ater spending a ew dayson campus meeting with members o the Department, theAdministration, and the Radiation Laboratory, my returnhome to Murray Hill, New Jersey, was the beginning o anemotional roller-coaster ride or my amily and me.

When we nally accepted the Notre Dame oer andmade the move in 1975, we were welcomed into the NotreDame community in grand style. My ormal inaugurationinvolved an installation ceremony, inaugural lecture, a Mass

honoring Charles and Catherine Huisking, a dinner honor-ing the Huisking amily, anda ootball game (Notre Damevs. Georgia Tech) with 50-yard-line seats. Although wedidnt realize it at the time, that game was to become me-morialized in the movie Rudy, as the game in which RudyRuettiger, a Notre Dame senior, nally gets to play.

The Spectrum: How useul are review articles? Doreview articles get enough attention? Should there be

more reviews?

Trozzolo: In 1980, as I began my ourth year as Editor oChemical Reviews, I wrote an editorial in which I pointedout the virtues o the scholarly art o writing review articles,one o which was its value o integrating and committing toposterity the knowledge and understanding that have beenaccumulated with much human eort. This rings as truetoday as it did in 1980, perhaps, even more so. In view o theever-increasing amount o research studies and publications,there is a continual need to upgrade and organize this newknowledge.

An indication o the stature and useulness o reviews isprovided by recent studies on citation data o publicationswhich shows that review journals have higher impact ac-tors (impact actor is the average number o citations per

source item) than other journals and thatChemical Reviewsconsistently has had the highest impact actor o any chemi-cal journal. Whether we need more reviews is answered bysaying that we are always in need o good reviews. By thatI mean reviews which are comprehensive, but not merelycatalogs o data. They need to be critical, with the hopeo being seminal in setting new paradigms or the subject.In my short essay at the beginning o the 100th volumeoChemical Reviews in 2000, I gave a ew examples o re-views published in that journal which have ullled thoseexpectations.

The Spectrum: Any advice or the sizable number ophotochemical scientists who are nearing retirement age?How can they avoid being eclipsed by younger aculty, or

make the best decision on whether to retire or work?

Trozzolo: My advice is aimed at academic scientists sincethe retirement o industrial scientists in recent years has o-ten been caused by economic actors beyond their control.My advice is this: I you are happy in what you are doingand have the nancial support to continue your research,dont retire. I, however, there are certain aspects o yourlie, people and places to visit, hobbies, etc., that haventreceived as much attention during your career as you would

like, then retirement has its attraction. For six years ater Ibecame emeritus, I was the Assistant Dean o the Collegeo Science and taught a course on Seeing the Light inScience which I designed rom scratch. It may be pos-sible to arrange a similar gradual change rom a ull-timeposition. I also wouldnt worry about being eclipsed by theyounger aculty. Its going to happen, sooner or later. Thatsactually one o the great satisactions o the academic career.To see your younger colleagues (whom you had a hand inchoosing) succeed in their elds.

The Spectrum: What pursuits keep you engaged today?

Trozzolo: My current activities these days divide up intothree groups: institutional, proessional, and amily. AtNotre Dame, I currently serve on the Faculty Senate rep-resenting the emeriti aculty. This gives me an opportunityto be in the loop regarding University aairs, and to try toinsure that the emeriti continue to be regarded as a valuableresource or the University community. I am still activelyinvolved with the ACS Local Section Speaker Service. Omy menu o ve dierent lectures, the one most oten cho-sen by the Sections is: Origins o Modern Photochemistryin ItalyA Lot o Bologna.

I have continued to be active with the Gordon Research

Conerences, attending at least one conerence a year sinceI became emeritus. The year 2006 is a special one or theConerences, marking their 75th Anniversary. The past yearhas been eventul or my wie, Dolly, and me as we cele-brated an event arranged by our children, our 50th weddinganniversary, and had a new house constructed so that we, inprinciple, could down-size. Six months ater we moved in,the down-sizing still continues.

The Spectrum: Is there any one question you wish we

had asked?

Anthony M. Trozzolo



13/32

Trozzolo: The question would be: What role did your wie,Dolly, play in your career? And the answer: Dolly has been aconstant source o support and encouragement throughoutthe 51 years o our marriage. From the sacrices o graduateschool when our amily was growing and our nancial statuswas barely viable to the absences caused by my increased

travel due to proessional commitments, she was the main-stay o our amilys welare. Once the children were older,she began to accompany me to meetings and on speakingtours, and has been to so many conerences on photochem-istry that she has a pretty good grasp o the vocabulary.

At Gordon Conerences, she urges rst-time coner-ees to network and get to know the leaders in the eld.Even Alex Cruickshank, long-time Director o the GordonConerences, once kidded her about being an honorary con-eree. When Father Theodore Hesburgh, while celebratingour 50th Anniversary Mass at Notre Dame last year, was giv-ing his homily about marriage, he mentioned: The Italianshave an expression to dene love. Its ti voglio bene which

literally means I wish you well. Dolly has been living thatdenition and it has refected on my career.

Anthony M. Trozzolo

Atthe1993PhysicalOrganicChemistryGordonConference.

Left-to-right:Tony,DollyTrozzolo,andAlexCruickshank

(DirectorEmeritusoftheGordonResearchConferences).



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assembly of dye aggregates on

nucleic acid nanotemplates

Bruce A. ArmitageDepartmentofChemistry,CarnegieMellonUniversity


My interest in photochemistry was rst engaged by anexperiment done as an undergraduate laboratory exerciseat the University o Rochester. The experiment involvedthe photoisomerization o trans- to cis-stilbene and subse-quent photo-oxidation to produce phenanthrene. Ater asemester spent dealing with oil baths and heating mantles,melting points and chromatography, what a joy it was touse a mercury lamp to drive a chemical reaction, and an HPUV-vis spectrophotometer to monitor the transormation.I suspect that most, i not all, readers oThe Spectrum, hadsimilar epiphanies that drew them into the wonderul eldo photochemistry. The proessor who introduced me tophotochemistry was David Whitten, who graciously over-

looked my mediocre perormance in the lecture componento the organic chemistry course he taught and gave me myrst research position. The goal o my project was to synthe-size various stilbazolium derivatives and study their photo-chemical dimerization reactions in reversed micelles. Well,this opened a second unoreseen door, namely perormingorganic chemistry in a solution that contained its own in-ternal structure. Micelles, liposomes, zeolites and clays areall examples o microheterogeneous or organized media andthe ability to assemble such structures within a solution o-ers the opportunity to alter and even control the outcomeo a photochemical reaction. The appeal o this notion wasreinorced not only by my time spent in the Whitten lab, butalso by a sparkling lecture given by Nick Turro at Rochesteron the occasion o his receiving the Harrison Howe Award.Turros talk was the rst time I had heard the term supra-molecular and it seemed to convey something bigger andbetter than what we were learning in the undergraduate cur-riculum. I was excited to learn more.

These experiences ultimately led me to pursue myPh.D. under the guidance o the late David OBrien at theUniversity o Arizona. OBrien taught me that supramolec-ular was not better than molecular, but rather that the twotypes o synthetic chemistry were complementary. Moreover,i molecular and supramolecular chemistry ailed to get you

to your destination, maybe a dose o macromolecular chem-istry would nish the job. Photochemistry was used to ini-tiate and sustain various polymerization reactions, particu-larly involving phospholipids that were pre-assembled intobilayer as well as other supramolecular assemblies. Thus, weused molecular chemistry to synthesize polymerizable lipids,supramolecular chemistry to sel-assemble the lipids into bi-layer or other structures, and nally macromolecular chem-istry to either stabilize or destabilize the resulting structure,depending on the goal o the experiments and compositiono the materials. In other projects, liposomes were used as

nano-concentrators to specically localize reactants at thebilayer surace or in the hydrophobic interior o the mem-brane (although we didnt use the prex nano much atthat time). Photoinduced electron and energy transer reac-tions were studied in these sel-assembled systems.1,2

Ater graduation, my path led me to Gary Schusters lab atthe University o Illinois, where we synthesized cationic an-thraquinone derivatives that would intercalate into double-helical DNA and upon irradiation, photo-oxidize the DNAbases, ultimately leading to permanent damage at specicsites.3 Readers will recognize the evolution o this project intothe study o electron and hole transport over long distances inDNA to which Schusters lab has contributed signicantly.

While Schuster and others were investigating photoin-duced electron transer in DNA, chemists, physicists andcomputer scientists were beginning to use DNA as a con-struction material or synthesizing elaborate, periodic nano-structures ranging rom planar, extended lattices4 to discreteobjects such as tetrahedra,5 octahedra6 and even smileyaces (J)7. Arrays consisting o metallic and semiconduct-ing nanoparticles or proteins were assembled using DNAtemplates.8 Again, we see the interplay o molecular, supra-molecular and macromolecular chemistry in this research.By way o this lengthy introduction, I will now describe aproject rom my own lab that ts into this context.

DNA-Templated Aggregation of Cyanine DyesThe binding o organic dye molecules to double-helical

DNA has enjoyed a long history. In act, the ability to stainnuclear material with basic dyes put the A (or acid) inDNA. Today, numerous dyes that either bind to the minorgroove o DNA or intercalate into the base pair stack arecommercially available and are widely used as fuorescentindicators or stains or DNA. Our interest in the interac-tion o organic dyes with DNA arose rom a desire to de-velop visible light sensitive photocleavage agents or DNAthat could be used in the lab as biological probes and/or inthe clinic or photodynamic therapy. This idea was based in

large part on work rom David OBriens lab, showing thatcyanine dyes can serve as eective photoinitiators or vinylpolymerizations and that the reaction mechanism likely in-volves generation o hydroxyl radical rom the excited statedye reacting with molecular oxygen.9 Since hydroxyl radicalis an eective DNA cleavage agent, this seemed like a rea-sonable track to ollow.

In our rst experiment, a symmetrical cyanine dye,DiSC

2(5) (Chart 1), was mixed with polymeric DNA

having an alternating A-T sequence. A simple UV-vis ex-periment revealed that the absorption spectrum o the dye


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Armitage


shited hypsochromically by 60 nm (Figure 1A).10,11 Thespectral shit is due to H-aggregation oDiSC2(5), pro-

moted by both the hydrophobicity and polarizability o theextended pi system o the dye. While aggregation can bedriven by increasing dye concentration or decreasing tem-perature,12 we discovered that it could also be promoted bydouble helical DNA. Thus, the DNA was serving as a tem-plate or the assembly o the dye aggregate.

Chart 1. Chemical structures o a cyanine dye, DNA andPNA.

An interesting eature o the DNA-templated aggregatewas that the UV-vis spectrum (Figure 1A) was noticeablynarrower than the spectrum o the dye in water. This con-trasts with dye H-aggregates that orm at high concentra-tions, which typically exhibit very broad absorption spectra,due to the presence o a plethora o structures varying innumber o dyes as well as relative orientations o dyes withinthe aggregate. Evidently, the DNA-templated aggregate hasa very well dened structure.

Spectroscopic experiments were used to identiy theDNA binding mode and structure o the aggregated dyes.

The sequence dependence o aggregation implicated theminor groove o the DNA as the likely binding site or thedyes, which was later conrmed by NMR experiments.13However, the blue shited absorbance avored binding o thedye as a coacial dimer rather than a monomer within thegroove. Additional dye molecules can also bind as dimers,aligned with other dimers in an end-to-end ashion, leadingto a helical aggregate in which the dyes wrap around theminor groove o the DNA template (Figure 2).

The helical structure o the cyanine dye aggregates leadsto interesting optical properties. For example, two orms oelectronic coupling are observed. First, there is the strongcoupling that arises between the two coacially stacked dyemolecules. This leads to splitting o the excited state, wheretransition to the upper state is allowed, while transitionto the lower state is orbidden, thereby accounting or theblue-shited absorbance spectrum (Figure 3). In addition, aweaker coupling occurs between end-to-end aligned dyes.This coupling is dicult to detect by UV-vis, although lowtemperature and high dye:DNA ratios promote broadeningor even splitting o the absorption band.14

The two types o coupling are more evident in the cir-

cular dichroism spectra o the dyes. Due to the symmetricalstructure o DiSC2(5), no CD signal is observed in solution.However, binding to the chiral DNA template leads to aninduced CD spectrum. For DNA templates on which a sin-gle, isolated dimer assembles, the CD spectrum is relativelyweak and yields a maximum at the same wavelength wherethe dimer absorbs in the visible. However, end-to-end align-ment o multiple dimers leads to the secondary coupling,which is maniested in the CD spectrum as strong excitonsplitting that refects the right-handed helical relationshipbetween the coupled dyes (Figure 1B).

Figure 1. UV-vis(A)andCD(B)spectrafor DiSC2(5)aggregates

assembledonaDNAtemplate.

Figure 2. Molecularmodelillustratingahelicalaggregateof

threeDiSC2(5)dimers(purple)assembledintheminorgroove

ofDNA.


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Armitage


Helical Aggregation of Cyanine Dyes on PNA

While the helical dye aggregates assembled on DNAtemplates have interesting structures and optical proper-ties, they have little applicability. However, we discovereda related phenomenon that led to a simple DNA detectionassay. The method involves PNA, a structural homologueo DNA in which the hydrogen bonding purine and py-rimidine bases are attached to a polyamide rather than apolyphosphodiester backbone (Chart 1). The bases in PNAextend rom the backbone with the same repeating distanceas in DNA allowing complementary PNA and DNA strandsto recognize one another and orm double-helical complex-es in the same way as two complementary DNA strands.15However, because o the lack o a negative charge along thePNA backbone, the anity o PNA or DNA is signicant-ly higher than between two DNA strands. Thus, PNA hasbeen used in a variety o DNA detection schemes.

The minor groove o PNA-DNA duplexes is wider than

that o DNA-DNA, but as noted above, there is a lowernegative charge density. Thus, it was not clear what dyes likeDiSC

2(5) would do in the presence o PNA-DNA. When

the dye was added to a solution containing a 12 base pairPNA-DNA duplex, the color o the solution was purple, incontrast to solutions o the dye alone or with DNA-DNA,where the color is invariably blue.16 The dierence in colorarises rom the act that the dye absorption spectrum in thepresence o PNA-DNA shits by 130 nm to the blue, com-pared with the 60 nm shit observed when the dye binds asa dimer in the minor groove o DNA (Figure 4A). Since

the larger shit indicates ormation o a more extended ag-gregate, we proposed assembly o an aggregate based on tri-meric units. (The helical structure o the aggregate is evi-denced by a strong exciton-split CD spectrum, as shown inFigure 4B.) The hypothesis that the aggregate is templatedby the PNA-DNA minor groove was supported by experi-ments that showed that steric blockage o the major groovedid not prevent dye aggregation, but blockage o the minorgroove did.17

These results demonstrate a simple colorimetric assay orDNA: i a complementary PNA binds to the DNA, then thedye aggregate can assemble and an immediate blue-purplecolor change is observed. This phenomenon has been thebasis or three dierent assays in which either the visiblecolor change or the induced CD spectrum is used to indicatethe presence o the DNA target.18-20 Sensitivity to singlemismatches can be introduced through temperature varia-tion or enzymatic degradation o mismatched duplexes.

DNA-Templated Multichromophore Arrays as

Fluorescent Labels

The helical dye aggregates assembled on DNA-DNA andPNA-DNA duplexes exhibit interesting and useul optical

shits and induced CD spectra. However, one troubling ea-ture o these systems is that the dye fuorescence is severelyquenched in these aggregates. There is great interest in syn-thesizing multichromophore arrays or light harvesting andfuorescent labeling applications. The DNA-templated ag-gregates assembled in the minor groove were appealing orthe ability to assemble large numbers o dyes in a small re-gion o space (ca. 2 dyes per 17 distance along the helix),but the quenched fuorescence precludes their use in fuores-cence labeling. An alternative strategy that retains DNA asa template while also hindering dye quenching is to exploit

Figure 4. UV-vis(A)andCD(B)spectrafor DiSC2(5)aggregates

assembledonadouble-helicalPNA-DNAtemplate.

Figure 3. Illustrationofexcitedstateenergylevelsplittingsand

allowedopticaltransitionsforH-aggregateddyes.

Monomer Dimer

Aggregate


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Armitage


a dierent binding mode or organic dyes with DNA: inter-calation. In this binding mode, the planar chromophore othe dye inserts between adjacent base pairs within the helix.In so doing, the DNA is strongly perturbed because it mustget longer and unwind in order to create the intercalationsite or the dye. This strongly inhibits binding o anotherdye at the same site, or even at an adjacent site. Rather,the dyes distribute themselves along the helix at every othersite. This allows one to load the DNA helix with a higheective concentration o dye while also keeping the dyemolecules at least two base pairs apart (ca. 7 ), enoughto prevent sel-quenching. The resulting intercalator arrayswill be intensely fuorescent. One can always create even

brighter assemblies by increasing the number o base pairsin the DNA template. This could involve making the DNAlonger, or resorting to branched structures such as thoseshown in Figure 5. Since DNA can be readily unctionalizedwith reactive groups or attachment to suraces or recogni-tion groups or binding to biomolecules, the DNA-dye ar-rays could be used as labels or tagging other molecules.

Conclusion

The assembly o cyanine dye aggregates and arrays onDNA-DNA and PNA-DNA templates blends molecular,supramolecular and macromolecular chemistry. Combining

old-school molecular recognition o DNA by minor groovebinders and intercalators with modern ideas rom the eld oDNA nanotechnology allows the ecient synthesis o newmaterials having a range o UV-visible, CD and fuorescencecharacteristics. It is hard to believe that 20 years have passedsince Dave Whitten rst introduced me to photochemistryand supramolecular assemblies.

References

1. Armitage, B.; Klekotka, P.; Oblinger, E.; OBrien, D. F.,J. Am. Chem. Soc. 1993, 115, 7920-7921.

2. Armitage, B.; OBrien, D. F.J. Am. Chem. Soc. 1991,113, 9678-9679.

3. Schuster, G. B.Acc. Chem. Res. 2000, 33, 253-260.4. Seeman, N. C. Chem. Biol. 2003, 10, 1151-1159.5. Goodman, R. P.; Schaap, I. A. T.; Tardin, C. F.; Erben,

C. M.; Berry, R. M.; Schmidt, C. F.; Turbereld, A. J.,Science 2005, 310, 1661-1665.

6. Shih, W. M.; Quispe, J. D.; Joyce, G. F.Nature 2004,427, 618-621.

7. Rothemund, P. W. K.Nature 2006, 440, 297-302.8. Gothel, K. V.; LaBean, T. H. Org. Biomol. Chem.

2005, 3, 4023-4037.9. Clapp, P. J.; Armitage, B.; OBrien, D. F.,

Macromolecules 1997,30, 32-41.10. Seiert, J. L.; Connor, R. E.; Kushon, S. A.; Wang, M.;

Armitage, B. A.J. Am. Chem. Soc. 1999, 121,2987-2995.

11. Hannah, K. C.; Armitage, B. A.Acc. Chem. Res.2004, 37, 845-853.

12. West, W.; Pearce, S.J. Phys. Chem. 1965, 69,1894-1903.

13. Hannah, K. C.; Gil, R. R.; Armitage, B. A.Biochemistry 2005, 44, 15924-15929.

14. Chowdhury, A.; Yu, L.; Raheem, I.; Peteanu, L.; Liu, L.A.; Yaron, D. J.J. Phys. Chem. A 2003, 107,3351-3362.

15. Egholm, M.; Buchardt, O.; Christensen, L.; Behrens,C.; Freier, S. M.; Driver, D. A.; Berg, R. H.; Kim, S. K.;Nordn, B.; Nielsen, P. E.Nature 1993, 365, 566-568.

16. Smith, J. O.; Olson, D. A.; Armitage, B. A.J. Am.Chem. Soc. 1999, 121, 2686-2695.

17. Dilek, I.; Madrid, M.; Singh, R.; Urrea, C. P.;Armitage, B. A.J. Am. Chem. Soc.2005,127,3339-3345.

18. Wilhelmsson, L. M.; Nordn, B.; Mukherjee, K.;Dulay, M. T.; Zare, R. N.Nucleic Acids Res. 2002, 30.

19. Komiyama, M.; Ye, S.; Liang, X.; Yamamoto, Y.;Tomita, T.; Zhou, J.-M.; Aburatani, H.J. Am. Chem.

Soc. 2003, 125, 3758-3762.20. Sorza, S.; Scaravelli, E.; Corradini, R.; Marchelli, R.,Chirality 2005, 17, 515-521.

About the AuthorBruce Armitage received his Ph.D. in chemistry rom the

University o Arizona in 1993. He is currently AssociateProessor o Chemistry and a member o the MolecularBiosensor and Imaging Center at Carnegie MellonUniversity. His e-mail is [email protected].

Figure 5. Illustration of DNA-templated arrays of uorescent

intercalatordyes.BranchedDNAnanostructuresallowahigher

densityofintercalateddyestobearrayed.


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the (photo)chemistry of anthocyanins

Frank H. Quina1, Adilson A. Freitas1,2, Antonio L. Maanita2, Palmira Ferreira da Silva2 & Joo Carlos Lima1InstitutodeQumica,UniversityofSoPaulo;2InstitutoSuperiorTcnico,TechnicalUniversityofLisbon;3REQUIMTE-FCT,NewUniversityofLisbon


Anthocyanins (rom the Greek words or fower, anthos,and blue, kyanos) constitute the major red and purple pig-ments in terrestrial plants,1,2 where they concentrate invacuoles in the cells o ruits, fowers and leaves (Figure 1).In fowers, anthocyanins attract insect pollinators, while incertain carnivorous plants they attract insect prey. Light-sensitive seedlings or plants subjected to excessive doses olight oten respond by synthesizing anthocyanins, presum-ably to protect the photosynthetic apparatus rom the excessincident radiation and photooxidative stress.3,4

Anthocyanins are omnipresent in our diet, have littleor no known toxicity and are usually quite water-soluble,making them particularly attractive as natural substitutesor synthetic pigments and antioxidants.1,2 However, inaqueous solution, most anthocyanins lose their color ratherrapidly at pH > 3. Thus, widespread practical application oanthocyanins as coloring agents will require novel strategiesor stabilizing their color at near-neutral pH, which in turnrequires a deeper understanding o the chemical and photo-chemical reactivity o anthocyanins.

The basic chromophore o anthocyanins is the

7-hydroxyfavylium ion (Chart 1). Naturally-occurring

anthocyanins typically have hydroxyl substituents at posi-tions 3 (always glycosylated, necessary or thermal stability)

and 5 (occasionally glycosylated) as well. The phenyl- orB-ring usually has one or more hydroxy or methoxy substitu-ents.1,2 Some o the most common natural anthocyanins areindicated in Chart 2. The colors o natural and synthetic

anthocyanins range rom yellow to purple (every color ex-cept green has been observed) and depend on the substitu-tion in the B-ring, the local pH, the state o aggregationo the anthocyanin or the occurrence o complexation byorganic molecules or, particularly in the case o blue colors,by metal cations as well.5,6 Although many hundreds o an-thocyanin structures have been reported in the literature,these dier primarily in the nature o the sugars present inthe glycosylated portions.

Rationalization o the chemical and photochemicalproperties o anthocyanins is quite complex. In the groundstate, natural anthocyanins can exist in acidic aqueous solu-tion (pH < 7) in at least ve dierent orms that are coupledto each other via pH-dependent equilibria1,2,7 (Scheme 1),while in basic solution this number can increase due to ad-ditional deprotonation equilibria. At pH < 3, the dominantorm is the red or purple favylium cation (AH+). AH+ is aweak acid (pK

ao the 7-hydroxy group in the range o 4-5)

that deprotonates to the blue quinonoidal base A. However,

favylium cations are subject to attack at C-2 by nucleo-philes such as water. Thus, at pH > 3, addition o water toorm the colorless or pale yellow hemiacetal (B) is otenmore avorable, leading to loss o the color. Tautomerismo the hemiacetal gives the cis-chalcone (C

cis), ollowed by

slow isomerization to the trans-chalcone (Ctrans

). At neu-tral pH, the dominant orm o anthocyanins is typicallythe hemiacetal (B), in equilibrium with minor amounts othe isomeric chalcones (C

cisand C

trans). In the rst excited

singlet state, 7-hydroxyfavylium ions are superphotoacids(pKa* < 0)

8, transerring a proton to water in about 6-20 ps,

Figure 1. Typicalanthocyanincolorsinfruit(grapes,

strawberries), leaves (poinsettia) and owers (blue hydrangea;

redroses).

Chart 1. The 7-Hydroxy-favylium Ion

Chart 2. Some o the More Common Naturally-OccurringAnthocyanins


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Quina, Freitas, Maanita, da Silva & Lima


and the chalcones can undergo photoisomerization and, asa consequence, exhibit photochromism.9

Scheme 1. Chemical transormations o oenin, a typicalanthocyanin, in aqueous solution.

Background for the Brazil-Portugal Collaboration

When we began our collaborative studies six years ago,several aspects o anthocyanin (photo)chemistry were com-pletely open questions. Although the ground-state proto-tropic reactions o the favylium cation can aect anthocy-anin color, the proton transer dynamics had not been de-termined or any o the natural or synthetic anthocyanins.There had been very ew systematic studies o the excited-state deactivation mechanisms and the possible ate o the

solar radiation absorbed in vivoand in vitroby anthocya-nins was completely unknown. Although ree anthocyaninsgenerally begin to lose their color at pH > 2.5-3 in aqueoussolution due to the onset o the hydration and tautomeriza-tion processes indicated in Scheme 1, evolution has devel-oped strategies or stabilizing the red color o anthocyaninsat pH values around 4-5 (the pH o plant cell vacuoles inwhich anthocyanins are located in vivo). In these vacuoles,complexation o the favylium cation by colorless copig-ment molecule such as hydroxylated benzoic and cinnamicacids, hydroxyfavones, and other polyphenols prevents

color bleaching by stabilizing the favylium cation with re-spect to the uncolored hemiacetal and chalcone orms.10The driving orce or this phenomenon, commonly reerredto as copigmentation, was generally assumed to be a hy-drophobic eect, perhaps combined with hydrogen bondinginteractions.

A key eature o our studies has been the use o mod-el synthetic anthocyanins (Chart 3) in which part o the

reactivity has been blocked or in which the charge or hydro-phobicity has been altered. Examples o the ormer includethe 4-methyl-7-hydroxyfavylium ion (HMF), in which hy-dration is disavored, allowing studies o the prototropic re-activity in the absence o the other ground-state multiequi-libria, and the 4-methyl-7-methoxy-favylium ion (MMF),in which the the prototropic equilibrium is blocked (Figure2). Examples o the latter include 7-hydroxyfavylium-4-carboxylic acid (CHMF),11,12 which is cationic at low pH

Chart 3. Synthetic Anthocyanin Probes

Figure 2.pH-DependentcolorofaqueoussolutionsofHMF

(pKa=4.4;predominantlyHA+atpH1-3andAatpH7),MMF

(nodeprotonation,hydrationatpH7)andOeninimmediately

afterpreparation(pKa=3.7;predominantlyHA+atpH1,Aat

pH7)andafterequilibrationfor6hinthedark(bleachingdueto

hydration,tautomerismandisomerizationatpH>2.5).


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(pK1 = 0.73), zwitterionic at intermediate acidic pHs (pK2= 4.84) and anionic at neutral pH, and water-insolubleanthocyanins with pendent aliphatic chains13 such as the6-(n-hexyl)-7-hydroxy-4-methyl-favylium ion (HHMF).When a simple compound that undergoes all o the(photo)chemical reactivity characteristic o natural antho-cyanins is required, the 4,7-dihydroxyfavylium ion (DHF)is a convenient choice. In most cases, the methodology de-veloped with these synthetic analogs has been extended torepresentative natural anthocyanins.

Ground and Excited State Proton-Transfer

Dynamics in Aqueous Solution

Excitation o synthetic anthocyanin analogs such asHMF and DHF in aqueous solution results in ultraast adia-batic excited-state proton transer (ESPT) to water in 6-10ps to produce the excited base orm (A*), which then de-cays to its ground state in about 100-200 ps.8 Since both theexcited state proton transer rom the excited acid AH+*and the subsequent decay oA* to its ground state are veryast, nanosecond laser fash photolysis can be employed toperturb the ground-state acid-base equilibrium and the de-protonation (k

d) and reprotonation (k

p) rate constants de-

termined by ollowing the relaxation back to equilibriumas a unction o pH.14 Since kobs = kd + kp[H

+], where kobsis the reciprocal o the lietime o the excess A producedby the laser pulse, a plot o kobs vs. [H

+] urnishes both theprotonation (slope) and deprotonation (intercept) rate con-stants (Figure 3). In addition, the act that pK a = log (kp/kd)provides a check on the values and a more precise valueo kd when the pKa is known independently. Interestingly,the values o kp and kd could also be readily determined orseveral natural anthocyanins by this method.7,15 Becausethe perturbation o the ground-state acid-base equilibriumby the laser pulse is a direct consequence o excited-stateproton transer, this constituted the rst evidence, albeit in-direct, or the occurrence o excited-state proton transer inthese naturally occurring anthocyanins.

Diglycosylated anthocyanins such as malvin, cyanin andpelargonin are only weakly fuorescent, while monoglycosyl-ated anthocyanins are practically non-fuorescent. Careulpicosecond time-resolved fuorescence measurements15 con-rmed the occurrence o ultraast (6-20 ps) adiabatic ESPTrom AH+* to water o several weakly-fuorescent naturalanthocyanins. Comparison o the fuorescence lietimeso the AH+* orm o anthocyanins (6-20 ps) with that oMMF (4.7 ns), in which proton transer is blocked, clearlyshows that highly ecient ESPT is the predominant pro-cess (>99%) responsible or the weak fuorescence o the

favylium cation orm o anthocyanins. This process is high-ly ecient as an energy-wasting mechanism and probablyserves to protect ree AH+* rom photodegradation androm intersystem crossing to the triplet state (that might po-tentially sensitize the ormation o singlet oxygen).

Proton-Transfer Dynamics at Micelle Surfaces

Micelles infuence the local pH16,17 and the relative sta-bilities o the various orms o the anthocyanin, resultingin shits in the pKas and in the pH-dependent speciation(relative proportions oAH+, A, B and the chalcones).7,18Employing the laser fash photolysis perturbation tech-nique, the protonation and deprotonation rates o antho-cyanins can also be determined at micelle suraces.7,12,18Reprotonation is diusion-controlled and involves encoun-ter oAwith a proton arriving rom the aqueous phase. Therates o both deprotonation and hydration are much slower

(by about 20-40-old) in aqueous micellar solution o theanionic detergent sodium dodecyl sulate (SDS) than in wa-ter, suggesting a specic stabilization oAH+ by the anionicmicellar environment. Conversely, inclusion o the antho-cyanin in cationic hexadecyltrimethyl ammonium chloride(CTAC) micelles results in a slight destabilization o theAH+ orm and, in the case oHMF, induces hydration andtautomerism not observed in water.18

Synthetic anthocyanins, in particular water-insolubleanthocyanins with hydrophobic side chains, have provento be excellent probes o proton transer dynamics at the

Figure 3. Laser ash photolysis perturbation of the ground state

acid-baseequilibriumofHMFasafunctionofsolutionpH(from

pH2.00-3.75);5nspulseat355nmfromaNd-YAGlaseratthe

arrow,absorbanceofAmonitoredat410nm.Thevariationof

theobservedrateconstantfordecayAwith[H+]isshowninthe

inset.BelowpH2.2,reprotonationoccursduringthelaserpulse.


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surace o detergent micelles.19,20 In bulk aqueous solution,8the kinetics o ESPT are straightorward with only two ki-netically and spectrally resolved species present, AH+* andA*. In contrast, studies oHMF in SDS and o the micelle-anchored probe HHMF in SDS and CTAC micelles haveshown that our kinetically resolvable species are present:two distinct populations oAH+* and two distinct popula-tions oA* (Scheme 2). One o the populations oAH+*is coupled to A* via ESPT, while the other (much longerlived) corresponds to AH+* molecules that are oriented atthe micelle surace in such a way as to inhibit the normalultraast ESPT. The two populations oA* are the initiallyormed geminate proton-anthocyanin base pair (H+A*),

which can either decay by ecient geminate reprotonationback to the acid or, upon proton escape, become reeA*.

Scheme 2. ESPT dynamics oHMF at the anionic SDSmicellar surace.

Copigmentation and the Excited-State Redox

Properties of Anthocyanins

Steady state fuorescence studies showed that the excit-ed singlet state oMMF is eciently quenched by typicalcopigment molecules. The quenching is static in nature anda consequence o the presence o ground state MMA-copig-ment complexes. Consequently, fuorescence quenchingprovides a convenient and straightorward method or de-termination o the equilibrium constants, K

cop, or complex

ormation or copigmentation.10,21 As expected or a process

dominated by charge-transer interactions, the log Kcop, val-ues or a variety o anthocyanin-copigment pairs correlatelinearly with the redox properties o the copigment (ioniza-tion potential, IP) and the anthocyanin (electron anity,EA). Thus, although there may be additional stabilizationo the anthocyanin-copigment complex by other actors,charge transer rom the copigment to the anthocyaninmakes a signicant contribution to the stability o anthocy-anin-copigment complexes and must clearly be taken intoaccount in any analysis o the copigmentation o anthocya-nins by colorless organic molecules.

Charge-transer complexation o the anthocyanins invivo has important consequences or color intensicationor copigmentation and or the photochemical stability oanthocyanins. From the standpoint o color stabilization,charge transer to the anthocyanin should decrease thepositive charge at carbon 2 o the favylium cation, result-ing in a reduction in the equilibrium constant or hydra-tion. Thus, charge transer nicely rationalizes the inhibitiono the hydration o the favylium ion upon complexationwith the copigment. The HA+ orm o anthocyanins isquite easily reduced10,21,22 and, hence, in the excited state,the cationic orm o anthocyanins turns out to be a superbelectron acceptor10,21 (Scheme 3). From the standpoint o

photostability, ecient static quenching o the excited stateo anthocyanin-copigment complexes via exergonic excitedstate electron transer (ESET) ollowed by ast back transerto give the ground state o the complex provides a highlyecient energy-wasting mechanism or copigmented antho-cyanins that protects them rom photodegradation.

Scheme 3. Excited singlet state redox properties o theAH+ orm o synthetic anthocyanins. Excitation energiesare in the range o 2.4-2.9 eV and reduction potentialstypically ca. -0.4 V.

Other Photoprocesses of AnthocyaninsNo consideration o the photochemistry o anthocyaninswould be complete without mention o their photochromicproperties.9,11 There are two important photochemical pro-cesses that can cause anthocyanin color changes: (1) cis-trans photoisomerization o the chalcones (C

cisand C

trans)

and (2) photocatalyzed ring closure o the cis-chalcone tothe hemiacetal (B) ollowed by acid-catalyzed loss o waterto give AH+. In the dark, the photogenerated AH+ thenreverts thermally back to the equilibrium mixture o AH+,B, C

cisand C

trans.


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Concluding RemarksIn the last ew years, we have made substantial progress in

understanding important aspects o the complex chemistryand photochemistry o anthocyanins. We now understandmany o the actors that aect the ground state equilibriao anthocyanins and can manipulate these equilibria (andhence anthocyanin color) in micellar media by appropri-ate choice o the detergent. We have characterized the dy-namics o proton transer in solution and at the surace omicelles and have demonstrated the importance o charge-transer interactions in anthocyanin-copigment complexes.ESPT and ESET have been shown to be the major energywasting processes via which uncomplexed and complexed

anthocyanins, respectively, convert the absorbed incidentradiation into heat without suering photochemical reac-tion. Studies in progress are directed towards the elucidationo the properties o the excited triplet state o favylium ionsin which proton transer has been blocked, such as MMF, astriplet sensitizers and as electron acceptors.

Acknowledgments

Funded in part by ICCTI/GRICES-CAPES and CAPES-GRICES international cooperation grants; in Brazil by grants(Universal 475337/2004-2) and ellowships rom the CNPqand ellowships rom CAPES and FAPESP; in Portugal bythe FCT (Proj. POCTI/QUI/38884/2001).

References

1. Bridle, P.; Timberlake, C. F. Food Chem. 1997, 58,103-109.

2. Brouillard, R.; Figueiredo, P.; Elhabiri, M.; Dangles, O.In Phytochemistry o Fruit and Vegetables;Toms-Barbern, F. A., Robins, R. J., Eds.; ClarendonPress: Oxord, 1997; Chapter 3, pp 29-49.

3. Hoch, W. A.; Singsaas, E. L.; McCown, B. H. PlantPhysiol. 2003, 133, 1296-1305.

4. Keskitalo, J.; Bergquist, G.; Gardestrm, P.; Jansson, S.Plant Physiol.2005, 139, 1635-1648.

5. Takeda, K.; Osakabe, A.; Saito, S.; Furuyama, D.,Tomita, A.; Kojima, Y.; Yamadera, M.; Sakuta, M.Phytochemistry2005, 66, 1607-1613.

6. Yoshida, K.; Kitahara, S.; Ito, D.; Kondo, T.Phytochemistry2006, 67, 992-998.

7. Lima, J. C.; Vautier-Giongo, C.; Melo, E.; Lopes, A.,Quina, F. H.; Maanita, A. L.J. Phys. Chem. A2002,106, 5851-5859.

8. Lima, J. C.; Abreu, I.; Santos, M. H.; Brouillard, R.;Maanita, A. L. Chem. Phys. Lett.1998, 298,189-195.

9. Pina, F.; Maestri, M.; Balzani, V. In Handbook oPhotochemistry and Photobiology; Nalwa, H. S., Ed.,American Scientic Publ.: Valencia, CA, 2003; Vol. 3,pp 412-450.

10. Ferreira da Silva, P.; Lima, J. C.; Freitas, A. A;Shimizu, K.; Quina, F. H.; Maanita, A. L.J. Phys.Chem. A 2005, 109, 7329-7338.

11. Freitas, A. A. Ph.D. Thesis, Instituto de Qumica,Universidade de So Paulo, 2006.

12. Paulo, L.; Freitas, A. A.; da Silva, P. F.; Shimizu, K.Quina, F. H.; Maanita, A. L.J. Phys. Chem. A2006,110, 2089-2096.

13. Fernandes, A. C.; Romo, C. C.; Rosa, C. P.; Vieira, V.

P.; Lopes, A.; Silva, P. F.; Maanita, A. L. Eur. J. Org.Chem.2004, 23, 4877-4883.

14. Maanita, A. L., Moreira, P.; Lima, J. C.; Quina, F.;Yihwa, C.; Vautier-Giongo, C.J. Phys. Chem. A2002,106, 1248-1255.

15. Moreira Jr., P. F.; Giestas, L.; Yihwa, C.; Vautier-Giongo, C.; Quina, F. H.; Maanita, A. L.; Lima, J. C.

J. Phys. Chem. A2003, 107, 4203-4210.16. Bunton, C. A.; Nome, F. J.; Quina, F. H.; Romsted, L.

S.Accts. Chem. Res.1991, 24, 357-364.17. Quina, F. H.; Lissi, E. A.Accts. Chem. Res.2004, 37,

703 - 710.18. Vautier-Giongo, C.; Yihwa, C.; Moreira Junior, P. F.;

Lima, J. C.; Freitas, A. A.; Alves, M.; Quina, F. H.;Maanita, A. L. Langmuir2002, 18, 10109-10115.

19. Giestas, L.; Yihwa, C.; Lima, J. C.; Vautier-Giongo,C.; Lopes, A.; Quina, F. H.; Maanita, A. L.J. Phys.Chem. A 2003, 107, 3263-3269.

20. Rodrigues, R.; Vautier-Giongo, C.; Silva, P. F.;Fernandes, A. C.; Cruz, R.; Maanita, A. L.; Quina, F.H. Langmuir2006, 22, 933-940.

21. Ferreira da Silva, P.; Lima, J. C.; Quina, F. H.;Maanita, A. L.J. Phys. Chem. A2004, 107,3263-3269.

22. Freitas, A. A.; Shimizu, K.; Dias, L. G.; Quina, F. H.

A Computational Study o Substituted FlavyliumSalts and their Quinonoidal Conjugate-Bases: S0gS1Electronic Transition, Absolute pKa and ReductionPotential Calculations by DFT and SemiempiricalMethods, submitted or publication.

About the Authors

Frank H. Quina received his Ph.D. rom Caltech in 1973(with George S. Hammond) and was a postdoctoral ellow atUNC-Chapel Hill (with David G. Whitten) beore movingto Brazil in 1975. He is currently Proessor at the Instituto



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de Qumica o the University o So Paulo (IQ-USP) in SoPaulo and Vice-Coordinator o the new USP Center orEnvironmental Training and Research in Cubato, SP. Hise-mail is [email protected].

Antnio L. Maanita received his Ph.D. in Chemistry in1981 rom the Instituto Superior Tcnico (IST), TechnicalUniversity o Lisbon (with Slvia B. Costa) and was apostdoctoral ellow with Klaas A. Zachariasse at the Max-Planck-Institut r Biophysikalische Chemie (Gttingen).From 1989 to 2001, he headed the Photochemistry Unito the Instituto de Tecnologia Qumica e Biolgica (ITQB,Oeiras), while lecturing at the IST. He is currently Proessoro Chemistry at the IST and leads the Group or Fast Kinetics

at the CQE (since 2002). His e-mail is [email protected] Carlos Lima received his Ph.D. in Chemistry in

1996 rom the IST in Lisbon (with Antnio L. Maanita)and was a postdoctoral ellow at the ITQB. He is currentlyan Assistant Proessor o Chemistry, Universidade Nova deLisboa, and part o the Photochemistry and SupramolecularChemistry research unit that integrates REQUIMTE, astate-associated laboratory devoted to the development ogreen processes. His e-mail is [email protected].

Adilson A. Freitas received his Ph.D. degree rom IQ-USP in 2005 (with F. H. Quina). He is currently a postdoc-toral ellow in the IST in Lisbon (with A. L. Maanita). Hise-mail is [email protected].

Palmira Ferreira da Silva received her Ph.D. in ChemicalEngineering rom the IST, Lisbon, in 1996 (with Jos A.M. Simes). She is currently Proessor Auxiliar in theDepartment o Chemical Engineering at the IST, Lisbon.Her e-mail is [email protected].

Publications from The Center for Photochemical

Sciences at Bowling Green State University

591. Porta, D.; Bullerjahn, G. S.; Twiss, M. R.;Wilhelm, S. W.; Poorvin, L.; McKay, R. M. L. Ironbioavailability in Lake Erie (Laurentian Great Lakes)measured by means o a cyanobacterial bioreporter.J.

Great Lakes Res. 2005, 31, 180-194.592. Anula, A. M.; Myshkin, E.; Guliaev, A.; Luman, C.R.; Danilov, E. O.; Castellano, F. N.; Bullerjahn,G. S.; Rodgers, M. A. J. Photo Processes on Sel-Associated Cationic Porphyrins and PlastocyaninComplexes 1. Ligation o Plastocyanin Tyrosine83 onto Metalloporphyrin and Electron TranserFluorescence Quenching. J. Phys. Chem. A2006,110, 2545-2559.

593. Anula, H. M.; Berlin, J. C.; Wu, H.; Li, Y.-S.; Peng,X.; Kenney, M. E.; Rodgers, M. A. J. Synthesis and


Photophysical Properties o Silicon Phthalocyanineswith Axial Siloxy Ligands Bearing AlkylamineTermini.J. Phys. Chem. A2006, 110, 5215-5223.

594. Hua, F.; Kinayyigit, S.; Cable, J. R.; Castellano,F. N. Platinum(II) Diimine Diacetylides:Metallacyclization Enhances PhotophysicalProperties. Inorg. Chem. 2006, 45, 4304-4306.

595. Polyansky, D.; Danilov, E. O.; Castellano, F. N.Direct Interrogation o Triplet Intraligand ExcitedStates Using Nanosecond Step-Scan FT-IR. Inorg.Chem.2006, 45, 2370-2373.

596. Montes, V. A.; Pohl, R.; Shinar, J.; Anzenbacher,P., Jr. Eective Manipulation o Electronic

Eects on the Emission o 5-Substituted Tris(8-quinolinolate)Al(III) Complexes. Chem. Eur. J.2006, 12, 4523-4535.

597. Nishiyabu, R.; Anzenbacher, P., Jr. 1,3-Indane-Based Chromogenic Calixpyrroles with Push-PullChromophores: Synthesis and Anion Sensing. Org.Lett.2006, 8, 359-362.

598. Hassler, C. S.; Twiss, M. R.; McKay, R. M. L.;Bullerjahn, G. S. Optimization o a cyanobacterial(Synechococcus sp. PCC 7942) bioreporter tomeasure bioavailable iron.J. Phycol.2006, 42,324-335.

599. Gouvea, S. P.; Melendez, C.; Carberry, M.;Bullerjahn, G. S.; Langen, T. A.; Twiss, M. R.Assessment o phosphorus-microbe interactions inLake Ontario by multiple techniques.J. Great LakesRes.2006, 32, 455-470.

600. Wilhelm, S. W.; Bullerjahn, G. S.; Rinta-Kanto, J.M.; Eldridge, M. L.; Bourbonniere, R. A. Seasonalhypoxia and the genetic diversity o prokaryotepopulations in the central basin hypolimnion o LakeErie: evidence or abundant picocyanobacteria andphotosynthesis.J. Great Lakes Res.2006, 32,657-671.

601. Islangulov, R. R.; Castellano, F. N. Photochemical

Upconversion: Anthracene Dimerization Sensitizedto Visible Light Using Ru(II) Chromophores.Angew.Chem. Int. Ed. 2006, 45, 5957-5959.

602. Ermoshkin, A. A.; Neckers, D. C.; Fedorov, A. V.Photopolymerization Without Light. Polymerizationo Acrylates Using Oxalate Esters and HydrogenPerioxide. Macromolecules2006, 39, 5669-5674.


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mono- and oligo-ruthenium(II) complexes

of tridentate ligands

Garry S. HananDepartment of Chemistry, University of Montrea


One o the biggest challenges acing humanity is theever-growing demand or energy, particularly as the worldspopulation should rise to near 10 billion by 2050.1 One couldthen ask: Will there be enough energy available to powerthe Earth, even at todays level o energy consumption? Oil,gas, coal, and nuclear energy are non-renewable resourcesthat may not last into the next century, however, alterna-tive orms o energy, or example, wind and solar energy,are renewable and have the potential to power humanityor centuries to come.2 Although direct conversion o windand solar energy into electricity is a very promising avenueo research, its conversion into chemical energy could ad-dress important issues such as how to store energy without

signicant losses. The advent o eective uel cell technolo-gies based on hydrogen also leads to the question o how toproduce large quantities o hydrogen without making use onon-renewable resources. Thus, the production o hydrogenby way o solar energy conversion appears to be an eectivemeans to meet some o the worlds uture energy needs.1

Although research into the photo-generation o hydro-gen expanded rapidly in the 1970s due to increasing oil pri-ces, there had been a lull in research as oil prices droppedover the 1980s and 1990s. The recent sustained increase inthe price o oil over the last ve or so years has reinvigoratedthe eld as has an increased understanding o how Natureproduces chemical energy. Many researchers are inspired bythe natural photosynthetic systems ound in green plantsand bacteria, which produce vast quantities o chemicalenergy rom sunlight everyday. These natural systems arehighly evolved and complex to the po

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