Page 1
Photochemistry:
Ring opening;
Bond dissociation etc.
Photophysics:
Intersystem crossing,
Spin crossover etc.
Time / seconds 10-15 10-12 10-6 10-3
S1
S0
T1
T2
S2
Aditi Bhattacherjee Marie Curie Fellow
AMOLF, The Netherlands
Photobiology:
Enzyme action, Radical polymerization,
Photocatalytic Reaction, etc.
Mapping Light-induced Chemical Dynamics
in Organic Rings from Ultrafast to Ultraslow
Page 2
Organic Rings
Carbon Catenation Functional Matter:
Charge transfer requires heteroatoms
Heterocyclic Rings
Porphyrins
Nucleobases
Natural
Products
Carbon chains
Carbon rings
Page 3
Ring Opening
Ring opening
Vitamin-D synthesis in skin in the presence
of sunlight
Biological significance Technological significance
7-dehydrocholesterol
Changes color in the presence of light
Spiropyran
Ashfold et al., JPCL (Perspective) 8, 3440, 2017
Kortekaas et al., ChemSocRev, 48, 3406, 2019
Anderson et al., JPCA, 103, 10730, 1999
Fuss et al., JPC, 100, 921, 1996
Page 4
Time / seconds 10-15 10-12 10-6 10-3
Breaking and Making of Chemical Bonds
S1
S0
T1
T2
S2
A A* hν
(Excited state) (Ground state)
B A A* A* + X Y A*
(triplet)
(singlet)
Complex Reactions:
Enzyme action, Radical polymerization,
Photocatalytic Reaction, etc.
Photochemistry:
Ring opening; Isomerization;
Bond dissociation etc.
Photophysics:
Intersystem crossing,
Spin crossover etc.
Page 5
Time / seconds 10-15 10-12 10-6 10-3
Breaking and Making of Chemical Bonds
S1
S0
T1
T2
S2
A A* hν
(Excited state) (Ground state)
B A A* A* + X Y A*
(triplet)
(singlet)
Photochemistry:
Ring opening; Isomerization;
Bond dissociation etc.
Photophysics:
Intersystem crossing,
Spin crossover etc.
Complex Reactions:
Enzyme action, Radical polymerization,
Photocatalytic Reaction, etc.
Page 6
Time / seconds 10-15 10-12 10-6 10-3
Breaking and Making of Chemical Bonds
S1
S0
T1
T2
S2
A A* hν
(Excited state) (Ground state)
B A A* A* + X Y A*
(triplet)
(singlet)
Photochemistry:
Ring opening; Isomerization;
Bond dissociation etc.
Photophysics:
Intersystem crossing,
Spin crossover etc.
Complex Reactions:
Enzyme action, Radical polymerization,
Photocatalytic Reaction, etc.
Page 7
Time / seconds 10-15 10-12 10-6 10-3
Evolving Electronic and Nuclear Structures
S1
S0
T1
T2
S2
A A* hν
(Excited state) (Ground state)
B A A* A* + X Y A*
(triplet)
(singlet)
Vitam
in D
synth
esis
,
Vis
ion
Photo
redox C
ata
lysis
Poly
mer
Synth
esis
/
Mole
cula
r re
cognitio
n
Photochemistry:
Ring opening; Isomerization;
Bond dissociation etc.
Photophysics:
Intersystem crossing,
Spin crossover etc.
Complex Reactions:
Enzyme action, Radical polymerization,
Photocatalytic Reaction, etc.
Page 8
Chemical Reactivity and Bonding
in Small Organic Molecules
Page 9
The Periodic Table of Elements
s orbital
s block
p orbitals
p block
Page 10
Chemical Bonding
Combining Atomic Orbitals to form Molecular Orbitals
Linear Combination Overlap and Mixing
φ1, φ2
𝟏
√𝟐 (φ1 + φ2)
𝟏
√𝟐 (φ1 - φ2)
σ
σ*
Energ
y
Page 11
Chemical Bonding
Linear Combination Overlap and Mixing
φ1, φ2
𝟏
√𝟐 (φ1 + φ2)
𝟏
√𝟐 (φ1 - φ2)
Energ
y
Combining Atomic Orbitals to form Molecular Orbitals
π
π*
Page 12
“Visualizing” Chemical Reactions: Connecting Electronic Energy with Nuclear Motion
+
Internuclear Distance (Bond length)
Page 13
“Visualizing” Chemical Reactions: Connecting Electronic Energy with Nuclear Motion
π2
ππ*
πσ*
Internuclear Distance (Bond length)
Page 14
Chemistry of Excited Electronic States
Peak-to-peak energy separation
• Easy bond activation
• Clean, targeted chemical reactions
(often, not always!)
• Central to photosynthesis, photoredox
catalysis, photoelectrochemistry etc.
Energ
y
Reaction coordinate
Time-resolved electronic (X-ray) absorption spectroscopy
Reaction coordinate
Methodology
Page 15
Attar, Bhattacherjee and Leone
JPhysChemLett. 6, 5072, 2015
(Editors’ Choice)
Bhattacherjee, Attar and Leone
JChemPhys 144, 124311, 2016
(Editors’ Choice)
Pump-Probe Spectroscopy
Attar, Bhattacherjee, Das, Schnorr,
Closser, Prendergast, and Leone
Science 356, 54, 2017
Bhattacherjee, Das, Schnorr, Attar
and Leone
JAmChemSoc 139, 46, 2017
4.66 eV (266 nm)
30-300 eV (40-4 nm)
Reaction coordinate Reaction coordinate
Pote
ntial energ
y
Pote
ntial energ
y
Probing Photochemical Reactions with an X-ray pulse
via Excitation of Core Electrons
Potential Energy Curves
Optical
X-ray
Page 16
Ultrafast Photochemistry:
Ring opening; Isomerization;
Bond dissociation etc.
Non-adiabatic Photophysics:
Intersystem crossing,
Spin crossover etc.
Time / seconds 10-15 10-12 10-6 10-3
Evolving Electronic and Nuclear Structures
S1
S0
T1
T2
S2
Fs X-ray Transient
Absorption Spectroscopy
Bimolecular Reactions:
Enzyme action, Radical polymerization,
Photocatalytic Reaction, etc.
Page 17
Ionization Continuum
X − Y
NEXAFS
EXAFS
Near-Edge X-ray Absorption Fine Structure
Extended X-ray Absorption Fine Structure
Typical X-ray Absorption Spectrum
Energ
y→
NEXAFS Spectroscopy, Stohr (Springer 1996)
Valence
σ, π orbitals
σ*, π* orbitals
Core 1s, 2s, 2p, etc.
Page 18
1. Element Specific
Advantages of using X-ray Probe
NEXAFS Spectroscopy, Stohr (Springer 1996)
Photon energy/eV
Inte
nsity
Page 19
2. Orbital Specific
Advantages of using X-ray Probe
Carbon K-edge Nitrogen K-edge
Carbon Nitride
Thomas et al., J. Mater. Chem., 18, 4893, 2008 Photon energy/eV
Inte
nsity
Page 20
3. Chemical Site Specific 1s→π* core-to-valence resonance
Photon energy/eV
Inte
nsity
Baldea et al., J. Elec. Spec. and Rel. Phen., 154, 109, 2007
Advantages of using X-ray Probe
Page 21
Tabletop X-rays: 30-320 eV, 35-70 fs
I Br Si P S Cl C Be B
Stephen R.
Leone
Andrew
Attar
Kirsten
Schnorr
Zheyue
(Marina) Yang
Tian
(Chris) Xue
University of California, Berkeley
Lawrence Berkeley National Laboratory 1) Broadband
2) Energy-Tunable 3) Multiple Absorption Edges
Photon energy / eV
Bhattacherjee and Leone AccChemRes 21, 3203, 2018
Page 22
Photochemical Reactions Studied
A-BAND PHOTODISSOCIATION OF HALOGENATED ALKANES
PERICYCLIC RING OPENING IN 1,3-CYCLOHEXADIENE
HETEROCYCLIC RING OPENING IN FURFURAL
ULTRAFAST INTERSYSTEM CROSSING IN ACETYLACETONE
BOND-SELECTIVE PHOTODISSOCIATION IN DIMETHYLDISULFIDE
Science 356, 6333, 2017
JACS 139, 46, 2017
JPCL 13, 82, 2019
JACS 140, 12538, 2018
JPCL 6, 24, 2015 (Editors’ Choice); JCP 144, 12, 2016 (Editors’ Choice); JACS 140, 41, 13360, 2018
Page 23
Ultrafast Ring Opening:1,3-Cyclohexadiene
1A
1B 2A
Potential energy surface
Reaction co-ordinate
En
erg
y
cZc, HT tZt, HT
Pericyclic
Minimum
tZc, HT CHD
Page 24
Electronic Structure
2A 1B
1A
1A(HT)
Page 25
Theoretical X-ray Spectra
1B
1A
2A
1A
(HT)
Page 26
Ground State Absorption Spectrum of 1,3-
Cyclohexadiene (CHD)
Peak A: 284.2 eV, 1s→1π*(C=C)
Peak B: 287.2 eV, 1s→2π*(C=C)
1s→σ*(C-C,C-H)
2π*
1π*
2π
1s
Attar, Bhattacherjee, Das, Schnorr, Closser, Prendergast, and Leone Science 356, 54, 2017
Peak A
(1s1π*) Peak B
Pe
ak
A
Pe
ak
B
Page 27
Carbon K-edge Transient Absorption
Spectra (CHD)
Experiment Theory 1B
Δt = 0 to 40 fs
Peak B
Photon energy / eV
Absorb
ance /
OD
Photon energy / eV
Am
plit
ude /
(arb
. unit)
Attar, Bhattacherjee, Das, Schnorr, Closser, Prendergast, and Leone Science 356, 54, 2017
Peak A
1B State
(2π)
Page 28
Δt = 90 to 130 fs
Carbon K-edge Transient Absorption
Spectra (CHD)
Photon energy / eV
Absorb
ance /
OD
Photon energy / eV
Am
plit
ude /
(arb
. unit)
Experiment Theory 2A
Attar, Bhattacherjee, Das, Schnorr, Closser, Prendergast, and Leone Science 356, 54, 2017
Page 29
1A
(HT)
Δt = 340 to 540 fs
Carbon K-edge Transient Absorption
Spectra (CHD)
Photon energy / eV
Absorb
ance /
OD
Photon energy / eV
Am
plit
ude /
(arb
. unit)
Experiment Theory
Attar, Bhattacherjee, Das, Schnorr, Closser, Prendergast, and Leone Science 356, 54, 2017
Page 30
CHD 1π*
2π/1π*
HT 1π*
REACTANT
PRODUCT
INTERMEDIATE VALENCE ELECTRONIC
STRUCTURE
(PERICYCLIC MINIMUM)
180 ± 20 fs
110 ± 60 fs
Attar, Bhattacherjee, Das, Schnorr, Closser, Prendergast, and Leone Science 356, 54, 2017
Ultrafast Ring-Opening Deconstructed
Page 31
O
O
πσ*
Carbon-Carbon Bond Fission Carbon-Heteroatom Bond Fission
1A
1B(ππ*)
2A(π*2)
π→π
*
S0
ππ*
π→π
*
HOMOCYCLIC RING OPENING
IN 1,3-CYCLOHEXADIENE
HETEROCYCLIC RING OPENING
IN FURFURAL
Two Ring-Opening Reactions at 266 nm
Science 356, 6333, 2017 JACS 140, 12538, 2018
Page 32
2π/1π*
Delayed rise ~ 60 fs
Decay ~110 fs
Ring opening ~ 350 fs
1s→π* 1s→π*
Das David Sven Regina
Attar et al.
Science 356, 6333, 2017
Bhattacherjee et al.
JACS 140, 12538, 2018
Kristina
284.5 eV 285.1 eV 286.4 eV
0.0
Two Ring-Opening Reactions at 266 nm
85
50
30
0
-50
30
10
0
-10
-20
LUMO (2p)
Page 33
What new science have we learnt?
X-ray vision catches Woodward-
Hoffmann
“The smooth evolution that occurs
in the vicinity of the pericyclic
minimum provides direct
affirmation of the W-H
framework. Moreover, the use
of a convenient tabletop
apparatus bodes well for future x-
ray studies of ultrafast electronic
dynamics.”
Yeston, Chemical Physics Editorial in
Science 356, 54-59, 2017
Discrimination of Ring-opened and
Ring-closed Isomers
“…Experimental studies capable of revealing the dynamics of
photoinduced ring-opening
processes are still in their infancy,
however. The challenges are
substantial…”
“…Without subsequent collisional
relaxation, measurement and
assignment of spectra of the
ring-opened species are
likely to be challenging.”
Ashfold and co-workers
JPCL (Perspective) 8, 3440, 2017
Page 34
Ring Puckering or Ring Opening?
What about nuclear structural dynamics?
Energ
y
Ele
ctr
onic
Page 35
What about nuclear structural dynamics?
2. Scattering
Time-resolved Hard X-ray Scattering
Minitti et al. PRL 114, 255501 (2015)
@ Stanford Linear Accelerator (SLAC)
Heteroatom NEXAFS
and
EXAFS
Ultrafast Electron Diffraction Wolf et al. NatChem 11, 504 (2019)
@ Stanford Linear Accelerator (SLAC)
1. Spectroscopy
Complementary Experiments
Page 36
Pentane-2,4-dione (Acetylacetone)
Intramolecular
O-H···O Hydrogen Bond
(12 kcal mol-1)
Enol (93%) Diketone (7%)
Equilibrium favors the enol form in the vapor phase
Ultrafast Intersystem Crossing in
Acetylacetone (AcAc)
Common chemical features of α,β-enones:
i) Keto-enol tautomerism
ii) Excited state intramolecular proton transfer
iii) Ultrafast excited-state relaxation
Irving et al., Acta Chem. Scand. 24, 589, 1970
Page 37
Xu et al., JPCA 108, 6650, 2004
Chen et al., JPCA 110, 13, 2006
Poisson et al., JACS 130, 2974, 2008
266 nm-Photodissociation in AcAc
Known so far
Production of OH radicals (~250 ps)
Multiple electronic states involved
Unknown
Role of the triplet state and intersystem crossing timescale
OO
H
+ OH 266 nm · ·
3-penten-2-on-4-yl
radical
Hydroxyl
radical AcAc
266 nm
Page 38
Carbon K-edge NEXAFS of AcAc
Bhattacherjee, Das, Schnorr, Attar and Leone JACS 139, 46, 2017
1s→π* (LUMO)
1s→Ryd
1s-Core Ionization
1
2
3
4
5
284.4
288.2
286.6
1s→π* (LUMO)
Unique signature of the enol tautomer at 284.4 eV
C3 is chemically shifted from C2 and C4 by ~2 eV
Photon energy / eV
Absorb
ance /
OD
Page 39
Transient Absorption Spectrum of AcAc
at Carbon K-edge 1 2
3 4
5
6
Early time-delays:
• Ground state depletion (peak 5)
• Appearance of new peaks 3,4,6
Long time-delays:
• Rise of peaks 1and 2
• Decay of peaks 3-6
Intermediate time-delays:
• Gradual decay of peaks 3-6
• Peak 3 broadens at the
lower energy wing
• Onset of new peak 1
Peak 1: 281.4 eV Peak 4: 285.9 eV
Peak 2: 283.8 eV Peak 5: 286.6 eV
Peak 3: 284.7 eV Peak 6: 288.4 eV
Photon energy / eV
ΔA
bso
rba
nce
/ m
OD
Bhattacherjee, Das, Schnorr, Attar and Leone JACS 139, 46, 2017
Page 40
Deconstructing AcAc Photophysics
280 282 284 286 288 290
Photon energy / eV
1 2
Faber et al., JChemPhys 151, 144107, 2019
Bhattacherjee, Das, Schnorr, Attar and Leone JACS 139, 46, 2017
Triplet
state,
ππ*
New Experiments are Benchmarking Theory
Time-dependent Density Functional Theory
Spin-adapted, Equation-of-motion
Coupled-Cluster Singles Doubles
Page 41
Mapping Chemical Reactions using
Ultrashort, Broadband X-rays
Attar, Bhattacherjee, Das, Schnorr, Closser, Prendergast, and Leone Science 356, 54, 2017
Bhattacherjee, Das, Schnorr, Attar and Leone JACS 139, 46, 2017
Bhattacherjee, Schnorr, Oesterling, Yang, Xue, Vivie-Riedle and Leone JACS 140, 39, 12538, 2018
Bhattacherjee and Leone AccChemRes 21, 3203, 2018
Stephen R.
Leone
Andrew
Attar
Kirsten
Schnorr
Zheyue
(Marina) Yang
Tian
(Chris) Xue
Leone Group
University of California, Berkeley
Lawrence Berkeley National Laboratory
Page 42
Future Research Goals
(1) Fundamental Dynamics
of Energy and Charge
(2) Revealing Biological
Function in Real Time
10-15 10-12 10-6 10-3 Time / seconds
Ring Opening and Ring Puckering
Ring Whizzing
Ring-Flip Enzyme Action
Why this? Why now? Why me? Why SLAC?
Page 43
Excited State Ring Dynamics
Knowledge Gap: Discrimination between ring opening and ring puckering channels
Approach: Time-resolved hard X-ray scattering at MHz repetition rates
Project 1a: Fundamental Dynamics of Energy and Charge
Page 44
• Nature’s machinery to safely dissipate harmful, excess electronic energy
• Of theoretical interest so far, now within the reach of experiments
Project 1a: Fundamental Dynamics of Energy and Charge
Excited State Ring Dynamics - Why Now?
Falahati et al., PCCP 20, 12483, 2018
Marian et al., PCCP 7, 3306, 2005
Satzger et al., PNAS 103, 10197, 2006
Ashfold et al., JPCL 8, 3440, 2017
Oesterling et al., PCCP 19, 2025, 2017
Bhattacherjee et al., JACS 140, 12538, 2018
Experim
ents
Perun et al., JACS 127, 6257, 2005
Perun et al., ChemPhys 313, 107, 2005
Marian et al., PCCP 7 , 3306, 2005
Page 45
Project 1a: Fundamental Dynamics of Energy and Charge
Excited State Ring Dynamics - Why Me? Bhattacherjee and Leone AccChemRes 21, 3203, 2018
Bhattacherjee, Schnorr, Oesterling, Yang, Xue, Vivie-Riedle and Leone JACS 140, 39, 12538, 2018
Attar, Bhattacherjee, Das, Schnorr, Closser, Prendergast, and Leone Science 356, 54, 2017
“No particular X-ray spectral
signatures are obtained to
specifically rule out the ring
puckering channel; however,
the estimates of internal
conversion to the ground
state indirectly set an upper
limit for this pathway”.
Rin
g o
penin
g in 1
00 f
s
Rin
g o
penin
g in 3
50 f
s
Page 46
Already demonstrated at LCLS: Ring opening and ring closing
New Capability at LCLS-II: Time-resolved hard X-ray scattering at MHz rep rates
Project 1a: Fundamental Dynamics of Energy and Charge
Excited State Ring Dynamics - Why SLAC?
Minitti et al., PRL 114, 255501, 2015 Wolf et al., NatChem 11, 504, 2019
Time-resolved hard X-ray scattering (8 keV) Time-resolved MeV electron diffraction
Page 47
Ring Whizzing Dynamics
Project 1b: Fundamental Dynamics of Energy and Charge
Knowledge Gap: Mechanisms and Timescales?
Approach: Molecular Movie of Ring Whizzing
(using time-resolved hard X-ray scattering at MHz repetition rates)
• Cope rearrangement
• Claisen rearrangement
• Wagner-Meerwein rearrangement
• Pinacol rearrangement
• Benzylic rearrangement
• Beckmann rearrangement
• Schmidt rearrangement
• Baeyer-Villiger rearrangement
• Criegee rearrangement
Moulay ChemEdu 3, 33, 2002
Example of ring-whizzing
Page 48
Ring Whizzing Dynamics - Why now?
Project 1b: Fundamental Dynamics of Energy and Charge
• Restricted to pen-and-paper understanding of structural rearrangements
(Isomerization), molecular fluxionality, C-H bond functionalization, etc.
• No experimental observations for the migration of a group of atoms
• Cope rearrangement
• Claisen rearrangement
• Wagner-Meerwein rearrangement
• Pinacol rearrangement
• Benzylic rearrangement
• Beckmann rearrangement
• Schmidt rearrangement
• Baeyer-Villiger rearrangement
• Criegee rearrangement
Moulay ChemEdu 3, 33, 2002
Page 49
Project 1b: Fundamental Dynamics of Energy and Charge
Time / seconds
10-12 10-6 10-3 10-9
Bhattacherjee, Sneha, Lewis-Borrell, Tau, Clark, and Orr-Ewing
Nature Communications 10, 5152, 2019 (Editors’ Focus on Energy Materials)
Ring Whizzing Dynamics - Why me?
Reaction mechanism of a multistep, photocatalytic
decarboxylation reaction in solution using a
100 kHz infrared laser
Page 50
Project 1b: Fundamental Dynamics of Energy and Charge
Ring Whizzing Dynamics - Why SLAC?
Jiang et al., PRL 105, 263002, 2010
Time-resolved photoionization of acetylene cation using a reaction microscope
@FLASH Germany
1,2
-Hyd
rog
en a
tom
sh
ift
Ibrahim et al., NatCommun 5, 4422, 2014
Coulomb Explosion Imaging of Acetylene Cation @Advanced Light Source Canada
Page 51
Revealing Enzyme Action
Project 2: Revealing Biological Functions in Real Time
Knowledge Gap: Is a ring flip mechanism operative in catalytic triads?
Approach: Femtosecond serial nanocrystallography at MHz repetition rates
Erez et al., Nature 459, 371, 2009
Page 52
Project 2: Revealing Biological Functions in Real Time
Revealing Enzyme Action – Why Now?
Ash et al., PNAS 97, 10371, 2000
• Catalytic triads are widely prevalent in the active site of serine hydrolases
• Known to accelerate peptide bond cleavage reactions by a factor of 1010
“Experimental evidence that the flipped rotamer can exist …
…supplied by an x-ray crystal structure of subtilisin BPN9 in 50%
dimethylformamide at low pH…
…In this structure, the imidazole ring is rotated 164°, rather than 180°…”
Page 53
Project 2: Revealing Biological Functions in Real Time
Revealing Enzyme Action – Why Me?
Bhattacherjee et al., PCCP 18, 27745, 2016
PCCP 17, 20080, 2015
Page 54
Project 2: Revealing Biological Functions in Real Time
“Diffract before destroy”
Revealing Enzyme Action – Why SLAC?
Ultrafast collective motions in myoglobin upon ligand dissociation
Barends et al., Science 350, 445, 2015
The resolution was 1.8 Å, owing to a temporarily reduced performance of the FEL, which limited the photon energy to 6.9 keV (l = 1.8 Å).
Page 55
Future Research Goals
10-15 10-12 10-6 10-3 Time / seconds
Ring Opening and Ring Puckering
Ring Whizzing
Ring-Flip Enzyme Action
Why this?
Why now?
Why me?
Why SLAC?
(1) Fundamental Dynamics
of Energy and Charge
(2) Revealing Biological
Function in Real Time
Mainly of theoretical interest / clues in static spectroscopy (ring flip) so far
Now within the reach of time-resolved X-ray experiments
Expertize in ring opening / broaden research horizon (enzyme action)
New opportunities for continued pioneering research in chemical dynamics