Time-Resolved Photoelectron Studies of Thiophene and 2,5-Dimethylthiophene
The photoinduced dynamics of thiophene and 2,5-dimethylthiophene (2,5-DMT) were investigated upon excitation at 200 and 255 nm (2,5-DMT only) using time-resolved photoelectron spectroscopy and compared with results from ab initio coupled cluster calculations. For thiophene, depopulation of the initi...
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Published in | The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 122; no. 45; pp. 8809 - 8818 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
15.11.2018
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Online Access | Get full text |
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Summary: | The photoinduced dynamics of thiophene and 2,5-dimethylthiophene (2,5-DMT) were investigated upon excitation at 200 and 255 nm (2,5-DMT only) using time-resolved photoelectron spectroscopy and compared with results from ab initio coupled cluster calculations. For thiophene, depopulation of the initially excited B2(π3π4*) state to the lower-lying A1(π2π4*) state occurs within 25 ± 20 fs, with a subsequent bifurcation into a ring-puckering channel and a ring-opening channel with lifetimes of 80 ± 20 and 450 ± 50 fs, respectively. For 2,5-DMT, the dynamics following excitation at 200 nm is described by a monoexponential decay with a time constant of 120 ± 20 fs, while that following excitation at 255 nm is best fit by a biexponential decay with time constants of 115 ± 20 fs and 15 ± 3 ps, respectively. The fast signal observed after excitation of 2,5-DMT is assigned to the ring-opening channel, which is favored with respect to thiophene due to a lower excited-state barrier along the ring-opening coordinate and an increased inertia toward the ring-puckering channel. Coupled cluster calculations have been undertaken to compare the relaxation dynamics of thiophene to thiazole and isothiazole. For the latter two molecules, we find a strong gradient along the ring-opening coordinate in the Franck–Condon region of the initially populated ππ* state and predict that ring-opening is the dominating relaxation channel after photoexcitation. We use the extracted information for a comparison of the thiophene dynamics with the light-induced processes observed in other five-membered heterocyclic molecules. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1089-5639 1520-5215 1520-5215 |
DOI: | 10.1021/acs.jpca.8b06728 |