Heinz B, Malkmus S, Laimgruber S, Dietrich S, Schulz C, Rück-Braun K, Braun M, Zinth W, Gilch P. Comparing a Photoinduced Pericyclic Ring Opening and Closure: Differences in the Excited State Pathways.
J Am Chem Soc 2007;
129:8577-84. [PMID:
17567132 DOI:
10.1021/ja071396i]
[Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The photochromicity of fulgimides rests on the existence of open (E) and closed ring (C) isomers. As predicted by the Woodward-Hoffmann rules both isomers can photochemically be interconverted. This interconversion has been studied by femtosecond fluorescence and transient absorption spectroscopy. For either direction (E --> C cyclization and C --> E cycloreversion) a biphasic fluorescence decay on the 0.1-1 ps time scale is observed. The longer time constants of the decays equal the formation times of the photoproducts. The time constants retrieved (0.06 and 0.4 ps for E --> C, 0.09 and 2.4 ps for C --> E) and the associated spectral signatures differ substantially. This indicates that no common excited-state pathway for the two directions exists, as one would infer from a simple Woodward-Hoffmann consideration. These findings support recent quantum dynamic calculations on the excited-state topology of fulgimides.
Collapse