Formation of Non-ketyl Radicals in the Photochemical Hydrogen Abstraction Reactions of Chromone Derivatives in theirππ* Triplet States as Studied by Time Resolved ESR*

AbstractStability is now a critical factor in the commercialization of organic photovoltaic (OPV) devices. Both extrinsic stability to oxygen and water and intrinsic stability to light and heat in inert conditions must be achieved. Triplet states are known to be problematic in both cases, leading to singlet oxygen production or fullerene dimerization. The latter is thought to proceed from unquenched singlet excitons that have undergone intersystem crossing (ISC). Instead, we show that in bulk heterojunction (BHJ) solar cells the photo-degradation of C60 via photo-oligomerization occurs primarily via back-hole transfer (BHT) from a charge-transfer state to a C60 excited triplet state. We demonstrate this to be the principal pathway from a combination of steady-state optoelectronic measurements, time-resolved electron paramagnetic resonance, and temperature-dependent transient absorption spectroscopy on model systems. BHT is a much more serious concern than ISC because it cannot be mitigated by improved exciton quenching, obtained for example by a finer BHJ morphology. As BHT is not specific to fullerenes, our results suggest that the role of electron and hole back transfer in the degradation of BHJs should also be carefully considered when designing stable OPV devices.

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Time-Resolved Resonance Raman Study of the Triplet States ofp-Hydroxyacetophenone and thep-Hydroxyphenacyl Diethyl Phosphate Phototrigger Compound

The Journal of Organic Chemistry ◽

10.1021/jo049331a ◽

2004 ◽

Vol 69 (20) ◽

pp. 6641-6657 ◽

Cited By ~ 15

Author(s):

Chensheng Ma ◽

Peng Zuo ◽

Wai Ming Kwok ◽

Wing Sum Chan ◽

Jovi Tze Wai Kan ◽

...

Keyword(s):

Resonance Raman ◽

Triplet States ◽

Time Resolved ◽

Raman Study ◽

Diethyl Phosphate

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Investigation of Carotenoid Radical Cations and Triplet States by Laser Flash Photolysis and Time-Resolved Resonance Raman Spectroscopy: Observation of Competitive Energy and Electron Transfer

Journal of the American Chemical Society ◽

10.1021/ja953181r ◽

1996 ◽

Vol 118 (7) ◽

pp. 1756-1761 ◽

Cited By ~ 44

Author(s):

J. H. Tinkler ◽

S. M. Tavender ◽

A. W. Parker ◽

D. J. McGarvey ◽

L. Mulroy ◽

...

Keyword(s):

Raman Spectroscopy ◽

Flash Photolysis ◽

Laser Flash Photolysis ◽

Resonance Raman Spectroscopy ◽

Radical Cations ◽

Laser Flash ◽

Triplet States ◽

Time Resolved ◽

Energy And Electron Transfer ◽

Spectroscopy Observation

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The photochemical reactivity of some benzoylthiophenes. IV. The effect of an adjacent methyl group on the excited state reactivity of 3-benzoylthiophene

Canadian Journal of Chemistry ◽

10.1139/v78-321 ◽

1978 ◽

Vol 56 (15) ◽

pp. 1970-1984 ◽

Cited By ~ 30

Author(s):

D. R. Arnold ◽

C. P. Hadjiantoniou

Keyword(s):

Hydrogen Abstraction ◽

Thiophene Ring ◽

Emission Spectra ◽

Photochemical Reactions ◽

Triplet States ◽

Photochemical Reactivity ◽

Methyl Group ◽

State Diagrams ◽

Phosphorescence Emission ◽

Intramolecular Hydrogen

The electronic absorption and phosphorescence emission spectra and the photochemical reactivity of several methyl-3-benzoylthiophenes (2- and 4-methyl-3-benzoylthiophene (1, 2), 2,5-dimethyl-3-benzoylthiophene (3), and 3-(2-methylbenzoyl)thiophene (4)) have been studied. Partial state diagrams have been constructed. The lowest energy absorption in hexane solution in every case is the carbonyl n → π* transition. The two lowest triplet states of these ketones are close in energy and, in fact, the nature of the emitting triplet (n,π* or π,π*) depends upon the position of methyl substitution and upon the solvent. The photochemical reactions studied include intramolecular hydrogen abstraction (revealed by deuterium exchange in the adjacent methyl group upon irradiation in perdeuteriomethanol solution), photocycloaddition of dimethyl acetylenedicarboxylate to the thiophene ring, and photocycloaddition of isobutylene to the carbonyl group. Generalizations, potentially useful for predicting photochemical reactivity of these and other aromatic ketones are summarized.

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