Center for Exploitation of Solar Energy & Department of Chemistry, University of Copenhagen Smart Materials & Structures, Las vegas, 15-17.6.2015 Tetrathiafulvalene-Fused Radiaannulenes and -Extended Tetrathiafulvalenes – Towards New Electrochromic Materials Mogens Brøndsted Nielsen
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Center for Exploitation of Solar Energy &
Department of Chemistry, University of Copenhagen
Smart Materials & Structures, Las vegas, 15-17.6.2015
Tetrathiafulvalene-Fused Radiaannulenes and -Extended Tetrathiafulvalenes
– Towards New Electrochromic Materials
Mogens Brøndsted Nielsen
Electrochromic Materials
- Reversibly changing color by electrochemical redox reactions
…. Redox-active molecules
Electrochromic Materials
- On/off switching of NIR absorptions?
Optical attenuator: device used to reduce the power level of an optical signal,
usually working by absorbing the light
Telecommunication industry: wavelengths of 1300 and 1550 nm
Both anodically and cathodically NIR-coloring materials are ideally needed
-Conjugated organic molecules
Wurster’s Blue
Wurster redox system: aromatic in reduced form
Blue color
N
N
N
N
N
N
- e
+ e
- e
+ e
Mixed Valence (MV)
fully delocalized
Tetrathiafulvalene (TTF)
S
S
S
S
S
S
S
S
S
S
S
S
TTF
- e
+ e
- e
+ eS S
S S
Mixed Valence (MV)
fully delocalized
Weitz redox system: aromatic in oxidized form
Tetrathiafulvalene
Some applications of TTF:
e-
e-
e-
Mixed valence
conduction
TTF / TTF•+
Properties can be tuned byintroduction of -spacer orsubstituents R
S
S
S
S
S
S
S
S
S
S
S
S
TTF
- e
+ e
- e
+ eS S
S S
Mixed Valence (MV)
fully delocalized
• Redox-active unit in supramolecular chemistry… molecular sensors, switches, and devices
• Redox-active unit in molecular electronics
• Mixed valence (TTF/TTF•+) organic conductors
• Electrochromic materials
Tetrathiafulvalene (TTF)
S
S
S
S
S
S
S
S
S
S
S
S
TTF
- e
+ e
- e
+ eS S
S S
Mixed Valence (MV)
fully delocalized
312 (369) nm
580 nm
390 nm
Radical Cation Absorptions
S
S S
S
S
S S
SMeS
MeS
SMe
SMe
S S
S S+
+
+
M.-B.S. Kirketerp, L.A.E. Leal, D. Varsano,A. Rubio, T.J.D. Jørgensen, K. Kilså,M.B. Nielsen, S.B. Nielsen, Chem. Commun. 2011, 47, 6900-6902.
Robin and Day Classification of Two-Center Redox Systems
Class III Cyclic Voltammogram
D D D DD D- e
+ e
- e
+ e
+ 2+Class III: Eox > 0.2 V
fully delocalized
Mixed Valence (MV)
Robin and Day Classification of Two-Center Redox Systems
Class I Class III Cyclic Voltammogram
D D
D D D DD D
Eox = Eox2 Eox1
- 2e
+ 2e
- e
+ e
- e
+ e
+ 2+
Class I: D
Class III:
D 2+ Eox ≈ 0 V (35 mV)
Eox > 0.2 V
Mixed Valence (MV)
fully delocalized
Robin and Day Classification of Two-Center Redox Systems
D D
D D D D D
D D D DD D
Eox = Eox2 Eox1
- 2e
- e
+ e
+ 2e
- e
+ e
- e
+ e
- e
+ e
+D
+ 2+
2+
Class I: D
Class II:
Class III:
D 2+ Eox ≈ 0 V (35 mV)
Eox ≈ 0 - 0.2 V
Eox > 0.2 V
Mixed Valence (MV)
fully delocalized
Class I Class III Cyclic Voltammogram
Electronic coupling: None
Potential Energy Surfaces for Electron Transfer in MV Systems
J. Hankache, O. S. Wenger, Chem. Rev. 2011, 111, 5138-5178.
Class IIClass I Class III
Weak
Broad NIR absorption
Strong
Narrow NIR absorption
Intermolecular MV Species – TTFTTF+
Figure 4. Spectral changes attendant upon the addition of neutral TTF to
the 5.8 mM solution of TTF+•CB- in CH2Cl2 at 22 C. TTF concentration
(bottom to top): 0, 44, 88, 141, 200, and 250 mM. Inset: Linear dependence
of ln KCT on 1/T.
S. V. Rosokha, J. K. Kochi, J. Am. Chem. Soc. 2007, 129, 828-838.
[TTF•TTF+]:
Kas = 6.0 M-1
Class II:
(2310 x max)1/2 = FWHM
[TTF+•TTF+]:
Kas = 0.6 M-1
Figure 2. Temperature-dependent absorption of 1.3 mM solutions of
TTF+•CB- in acetone, showing reversible interconversion between the
electronic spectrum of the monomer M (prevailing at room temperature)
and the dimer D (at low temperature). Temperature (in C, from bottom to
top at 740 nm): 22, - 40, - 55, - 63, - 70, - 78, - 85, and - 90. Inset:
Low-energy range of the absorption at high concentrations of TTF+·CB-
(λ ) 2 mm, 22 C). Concentration of TTF+•CB- (in mM, bottom to top):
0, 4.7, 6.2, 9.3, 13, and 19.
S. V. Rosokha, J. K. Kochi, J. Am. Chem. Soc. 2007, 129, 828-838.
-Dimer of Two TTF Radical Cations
D D
S
S S
S S
S S
S
SS
S S
• Redox properties?
• Optical properties of oxidized species?
• Interactions between redox centers?
Outline
Tetrathiafulvalene (TTF) – Acetylene Macrocycles
S
S
S
S
S
S
S
SEtS
EtS SEt
SEt
iPr3Si SiiPr3
S
S S
S
S S
S S
SS
RR
R
RR
R iPr3Si SiiPr3
TTF-Radiaannulene
Cross-conjugated cyclic core
S S
TTF-Dehydroannulene
Linearly conjugated cyclic core
How do the TTFs interact?
Synthesis of TTF-Dehydroannulenes
A. S. Andersson, K. Kilså, T. Hassenkam, J.-P. Gisselbrecht, C. Boudon, M. Gross,M. B. Nielsen, F. Diederich, Chem. Eur. J. 2006, 12, 8451.
K. Lincke, M. A. Christensen, F. Diederich, M. B. Nielsen, Helv. Chim. Acta 2011, 94, 1743-1753.
by Hay Couplings
S
S S
S
S
S
S S
S
SS
S
RR
R
R R
R
R = Pr, Hex, SEt
S
S
S
S
R
R
45-70%
Si(i-Pr)3
Si(i-Pr)3
1) Bu4NF, THF
S
S
S
S
R
R
2) CuCl, TMEDA
CH2Cl2, air
No - stacking interactions
The molecule does not seem either to associate in solution
X-Ray Crystal Structure
-0.50 -0.25 0.00 0.50 0.75 1.00
-4.0x10-5
-2.0x10-5
0.0
2.0x10-5
4.0x10-5
6.0x10-5
Cu
rre
nt
(A)
0.25
Potential (V)
Electrochemistry
S
S
S
S
S
SS
S
EtS SEt
S S
S S
SEt
SEtEtS
EtS
CH2Cl2 + 0.1 M Bu4NPF6
+1 +3
+6
Spectroelectrochemistry
M M+
M3+
M6+
MV absorption
CH2Cl2 + 0.1 M Bu4NPF6
S
S S
S
S
S
S
SS
S
EtS SEt
S S
SEt
SEtEtS
EtS
S
SS
S
S
S S
S
EtS
EtS SEt
SEt
(i-Pr)3Si Si(i-Pr)3
Si(i-Pr)3(i-Pr)3Si
S
S
S
SEtS
EtS I
I
(i-Pr)3Si Si(i-Pr)3
Pd(PPh3)4, CuI
iPr2NH10%
Synthesis of TTF-Radiaannulene
K. Lincke, A. F. Frellsen, C. R. Parker, A. D. Bond,O. Hammerich, M. B. Nielsen, Angew. Chem. 2012,
51, 6099-6102 .
by Sonogashira Couplings
A fused Weitz/Wurster-type redox system has been prepared by fusing a central
expanded radiaannulene core with two tetrathiafulvalene units. The system
formally gains H ! ckel aromaticity by either oxidation (6p-dithiolium units) or
reduction (14p-octadehydroannulene unit) and can exist in several redox states
with characteristic UV/Vis/IR absorptions. More about this system can be found in
the Communication by M. Brøndsted Nielsen and co-workers (DOI : 10.1002/
anie.201202324).
Size exclusion chromatography
SS
S
S
S
SS
S
Si(i-Pr)3(i-Pr)3Si
(i-Pr)3Si Si(i-Pr)3
EtS
EtS
SE
t
SE
t
Si(i-Pr)3(i-Pr)3Si
S
SS
S
EtS
EtSS
S
S
S SEt
SEt
Si(i-Pr)3(i-Pr)3Si
Si(i-Pr)3(i-Pr)3Si
MALDI MS
-3 -2 -1 0 1
-0.04
-0.02
0.00
-0.04
0.02
-0.02
0.00
-0.06
0.02
-0.04
-0.02
0.00
0.02
0.04-3 -2 -1 0 1
E/V
5
I/A
8
9
S
SS
S
S
S S
S
EtS
EtS SEt
SEt
(i-Pr)3Si Si(i-Pr)3
Si(i-Pr)3(i-Pr)3Si
S
SS
S
S
S S
S
EtS
EtS SEt
SEt
Si(i-Pr)3(i-Pr)3Si
S
S
S
SEtS
EtSSi(i-Pr)3
Si(i-Pr)3
Cyclic Voltammograms
+1+2
+2
+4
+1
+2
+4
9000 8000 7000 4000 3000 2000 1000
A
6000 5000
/cm-1
Neutral
Monocation
2250 2200 2100 2050
A
2150
/cm-1
7000
/nm
2000
FWHM = 2131 cm-1
Theory – Class II:
(2310 x max)1/2 = 3125 cm-1
Spectroelectrochemistry
S
SS
S
S
S S
S
EtS
EtS SEt
SEt
(i-Pr)3Si Si(i-Pr)3
Si(i-Pr)3(i-Pr)3Si
Radical cation: low-energy MV absorption
Si(i-Pr)3(i-Pr)3Si
S S
S S
BuS
BuS
S S
S S
SBu
SBu
S
S
S
S
BuS
BuS
S S
S S
SBu
SBu
Si(i-Pr)33(i-Pr) Si
S S
S S
BuS
BuS
S S
S S
SBu
SBu
Spectroelectrochemisty of Bis-TTFs
M M+M2+
MV absorptionMV absorption
MV absorption: short distance or cyclic structure
BJOC 2015, 11, 930-948.
-2 0 1-1
V vs Fc+/Fc
Cyclic voltammogram:
+1
+2
+4
-2
Mixed valence state:
max ca. 2250 nm
Neutral core: NICS()zz = -8.4 ppm
Dianion core: NICS()zz = -33.2 ppm
Gain in aromaticity (Wurster type)
6 redox statesS S
S S
S S
S SEtS
EtS SEt
SEt
(i-Pr)3Si Si(i-Pr)3
Si(i-Pr)3(i-Pr)3Si
-1
0
14
K. Lincke, A. F. Frellsen, C. R. Parker, A. D. Bond,O. Hammerich, M. B. Nielsen, Angew. Chem. Int. Ed.
2012, 51, 6099-6102 .
Hückel 4n+2
300 500 900 1100
A
700
/nm
Neutral
Monoanion
Neutral regenerated
Spectroelectrochemistry – Generation of Monoanion
S
SS
S
S
S S
S
EtS
EtS SEt
SEt
(i-Pr)3Si Si(i-Pr)3
Si(i-Pr)3(i-Pr)3Si
CT(neutral
compound)
S S
S
SS
S
S S
S
SS
S
SEtEtS
SEt
SEt
EtS
EtS
BC
E / eV (electrochemistry)
S S
S S
EtS
EtS
S S
S S
SEt
SEt
Si(i-Pr)3(i-Pr)3Si
Si(i-Pr)3(i-Pr)3Si
A
(i-Pr)3Si Si(i-Pr)3
S
SS
S S
SS
S
EtS
EtS SEt
SEt
HOMO-LUMO Gap Comparison of Neutral Compounds
1.9
1.85
1.8
1.75
1.7
1.65
1.6
1.55
1.5
1.45
1.4
1.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9
E
/eV
(U
V-V
is)
A
B
C
HOMO
LUMO
ABC
D D
SS
S S
• Redox properties?
• Optical properties of oxidized species?
• Interactions between redox centers?
Outline
S
S S
S S
S S
S
CH2Cl2 + 0.1 M NBu4PF6
Potentials vs Fc+/Fc
-0.25 0.00 0.25 0.75 1.00 1.25
-5.0x10-5
0.0
5.0x10-5
Curr
en
t (A
)
0.50
Potential (V)
ox
10 cycles
E = +0.72 V
Me3Si SiMe3
S
S
CO2Me
SMeO2C
CO2MeS
MeO2C
Me3Si SiMe3
S
S
CO2Me
SMeO2C
CO2MeS
MeO2C
Me
Me
Electrochemistry – Cyclic Voltammetry
Independent
redox centers
(Class I)
J. Am. Chem. Soc. 2014, 47, 16497−16507.
S S
S S
R R
RR'
S S
S S
R R
R R
- 2e
+ 2e
F.G. Brunetti, J.L. López, C. Atienza, N. Martín,J. Mater. Chem. 2012, 22, 4188-4205.
Potential Inversion
E2 < E1
C. A. Christensen,A. S. Batsanov, M. R. Bryce, J. Am. Chem. Soc. 2006, 128, 10484-10490.
Rigid Cyclophane
Intermediate radical cation
Extended TTFs
S
S S
S
TTF
S S
S S
S
S
S
S S
S
S
S
TTF2+S S
R R
RR
S S
S S
R R
R R
S S
S S
S S
S S
S S
S S
TTF +
S S
Intermediate?
Fully delocalized?
Indenofluorene-extended TTF
S S
S S
BuS SBu
O
BuS SBu
S S
SBuBuS
O
O
SS
S
BuS
BuS
P(OEt)3, 23%
S
S
BuS
BuS
O
P(OMe)2
NaHMDS, THF
69%
Synthesis ofIndenofluorene-Extended TTF
J. Mater. Chem. 2014, 2, 10428-10438.
0.8 0.6 0.4 0.2 0.0 -0.2
-30
-20
-10
10
20
ic-1/(
Am
M-1)
E/V 1.2 1.0
-10
-8
-6
-4
00
-2
2
4
i(
A)
0.8 0.6
E (V vs. Ag)
CH2Cl2 (0.1 M Bu4NPF6); Potentials vs Fc+/Fc
1 mM
0.06 mM
21 oC
-5.5 oC
0.25 mM
Cyclic Voltammetry
Concentrationdependence
21
16
10
3.5
-5.5
Temperature dependence
0.4 0.2
Intermolecular interactions
S S
S S
S S
S S
S S
S S
BuS SBu
BuS SBu
BuS SBu
BuS SBu
BuS SBu
BuS SBu
- e
+ e
- e
+ e
-30
-25
-20
-15
-10
-5
0
5
10
15
i/
A
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1
E/V
experimental
simulated
d2+ + e- c·+
c·+ + e- n
[c-c]2+ + e- [n-c]·+
[n-c]·+ + e- [n-n]
c·+ + c·+ n + d2+
c·+ + n [n-c]·+
[n-c]·+ + c·+ [c-c]2+ + n
[n-c]·+ + d2+ [c-c]2+ + c·+
c·+ + c·+ [c-c]2+
n + n [n-n]
redox-1
redox-2
redox-3
redox-4
Eq.-1
Eq.-2
Eq.-3
Eq.-4
Eq.-5
Eq.-6
n + [n-c]·+c·+ + [n-n]Eq.-7
c·+ + [n-c]·+d2+ + [n-n]Eq.-8
S S
SBu
Complexes:
neutral – neutral
neutral – cation
cation – cation
BuS
n
Simulation ofCyclic Voltammogram
S S
BuS
c+
SBu
S S
BuS
d2+
SBu
BuS SBu BuS SBu BuS SBu
S S S S S S
Spectroelectrochemistry
Relative intensities of low-energy
absorptions are concentration dependent
M M+M2+
/ nm
J. Mater. Chem. 2014, 2, 10428-10438.
M M+M2+
M+
M:M+
M+:M+
M+
M+:M+
S S
S S
BuS SBu
BuS SBu
Spectroelectrochemistry
MV Dimer:Kas = 7.8 x 104 M-1
-Dimer:Kas = 1.8 x 104 M-1
[TTF•TTF+]: Kas = 6.0 M-1
[TTF+•TTF+]: Kas = 0.6 M-1
S. V. Rosokha, J. K. Kochi, J. Am. Chem. Soc. 2007, 129, 828-838
After 10% conversion
After 90% conversion
Ottle cell
Progression from yellow to blue solution upon oxidation
(neutral to dication)
Electrocrystallization
Solvent: PhCl + counter electrolyte
S S
EtS SEt
S S
SEtEtS
a) b) c)
Cation•TaF6
Cation•PF6 Cation•Dication•(BF4)1.5 Cation•TaF6
J. Mater. Chem. 2014, 2, 10428-10438.
Conductances of Salts S S
S S
EtS SEt
SEtEtS
IFTTF
semiconductors
CAN WE ENHANCE THE CATION ASSOCIATIONS?
Incorporation of Fused Thiophene Units
S
S
BuS
BuS
O
P(OMe)2
S
S
S
S
S
BuS
SBu
S
SBu
SBu
S
S
O
O
S
SS
S
S
S
BuS
SBu
BuS
SBu
S
S
O
O
SS
S
S
RSS
SR SR
SRSO O
NaHMDS, THF
65%
R = Et (67%) R = Bu (64%)
S
S
BuS
BuS
O
P(OMe)2
NaHMDS, THF
40%
S
S
RS
RS
O
P(OMe)2
NaHMDS, THF
RSC Adv. 2015, 5, 49748-49751.
SS
S S
S
BuS
SBu SBu
SBu
Differential Pulse Voltammograms
S
SS
S
S
S
BuS
SBu
BuS
SBu
S
S
S
S
S
S
BuS
SBu
SBu
MV Dimer:
Kas = 1.8 x 104 M-1
-Dimer:
Kas = 2.8 x 103 M-1
Associations increase
(by one order
of magnitude)
SBu
RSC Adv. 2015, 5, 49748-49751.
SS
S S
S
BuS
SBu SBu
SBu
Differential Pulse Voltammograms
Oxidation Potentials
+0.14 V, +0.31 V
+0.32 V, +0.60 V
+0.09 V, +0.33 VS
S
S
S
S
S
BuS
SBu
SBu
SBu
S
SS
S
S
S
BuS
SBu
BuS
SBu
Linear conjugation
Cross-conjugation
(weakest donor)
SS
S
S
BuS S
SBu SBu
SBu
S
SS
S
S
S
BuS
SBu
SBu
S
S
S
S
S
S
BuS
BuS
SBu
SBu
SBu
Spectroelectrochemistry M M+M2+
Conclusions
S
S
S
S
S
SS
S
R R
S S
R
RR
R
S S
S S
S S
S SEtS
EtS SEt
SEt
iPr3Si SiiPr3
S S
TTF-Acetylene Macrocycles
Strong charge-transfer chromophores
Multiple redox states with distinct optical properties – molecules can both be oxidized and reduced
Interactions between TTFs are enforced
in the cyclic structures in comparison
to acyclic ones (MV absorptions of radical cations)
S S
S S
BuS SBu
SBuBuS
Indenofluorene-Extended TTFs
Strong associations between cations- Tectons for self-assembly
Broad UV-Vis-NIR absorptions
Thiophene units enhance donor strength
significantly when redox centers are
connected in linearly conjugated
pathway
S
S
S
S
S
S
BuS
SBu
SBu
SBu
iPr3Si SiiPr3
Combined Weitz and Wurster type redox system
University of Copenhagen:
Past and present group members:
Dr. Christian R. Parker
Dr. Mikkel A. Christensen
Dr. Karsten JennumDr. Marco Santella
Dr. Kasper Lincke
Dr. Søren Lindbæk Broman Dr. Virginia MazzantiPeter Bæch Abrahamsen
Emil GlibstrupMads Mansø
Huixin Jiang
Anders F. Frellsen
Cecilie L. Andersen
Prof. O. HammerichProf. Henrik G. Kjaergaard
Assoc. Prof. Thomas J. SørensenDr. Eduardo Della PiaDr. Theis Brock-NannestadT. J. Morsing