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Issue 9, 2005
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Femtosecond fluorescence up-conversion spectroscopy of a rotation-restricted azobenzene after excitation to the S1 state

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Abstract

Femtosecond time-resolved fluorescence up-conversion spectroscopy has been used in a study of the photo-induced isomerization reactions of a rotation-restricted trans-azobenzene (trans-AB) derivative capped by a crown ether (1), a chemically similar open derivative (2), and unsubstituted trans-AB (3) after excitation to the S1 (nπ*) state at λ = 475 nm in dioxane solution. The observed biexponential temporal fluorescence profiles for 1 and 2 were almost indistinguishable within experimental error. The fitted fast fluorescence decay times (±2σ) for the two compounds were τ1 (1) = (0.79 ± 0.20) and τ1 (2) = (1.05 ± 0.20) ps, compared to τ1 (3) = (0.37 ± 0.06) ps. The second decay components could be described with τ2 (1) = (20.3 ± 9.5) resp. τ2 (2) = (19.0 ± 6.0) ps, vs. τ2 (3) = (3.26 ± 0.85) ps. The very similar lifetimes strongly suggest that transcis isomerization of 1 and 2 after S1 excitation is governed by the same mechanism. Since 1 cannot isomerize by a simple large-amplitude rotation of one of the phenyl rings about the central NN bond, the isomerization dynamics of both ABs should be better described as “inversion” at the N atom(s) rather than large-amplitude “rotation”.

Graphical abstract: Femtosecond fluorescence up-conversion spectroscopy of a rotation-restricted azobenzene after excitation to the S1 state

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Article information


Submitted
23 Dec 2004
Accepted
24 Mar 2005
First published
11 Apr 2005

Phys. Chem. Chem. Phys., 2005,7, 1985-1989
Article type
Paper

Femtosecond fluorescence up-conversion spectroscopy of a rotation-restricted azobenzene after excitation to the S1 state

T. Pancur, F. Renth, F. Temps, B. Harbaum, A. Krüger, R. Herges and Chr. Näther, Phys. Chem. Chem. Phys., 2005, 7, 1985
DOI: 10.1039/B419236B

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