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Issue 7, 2012
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Sequential photoisomerisation dynamics of the push–pull azobenzene Disperse Red 1

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Abstract

The ultrafast dynamics of the push–pull azobenzene Disperse Red 1 following photoexcitation at λpump = 475 nm in solution in 2-fluorotoluene have been probed by broadband transient absorption spectroscopy and fluorescence up-conversion spectroscopy. The measured two-dimensional spectro-temporal absorption map features a remarkable “fast” excited-state absorption (ESA) band at λ ≈ 570 nm appearing directly with the excitation laser pulse and showing a sub-100 fs lifetime with a rapid spectral blue-shift. Moreover, its ultrafast decay is paralleled by rising distinctive ESA at other wavelengths. Global fits to the absorption–time profiles using a consecutive kinetic model yielded three time constants, τ1 = 0.08 ± 0.03 ps, τ2 = 0.99 ± 0.02 ps, and τ3 = 6.0 ± 0.1 ps. Fluorescence–time profiles were biexponential with time constants τ1′ = 0.12 ± 0.06 ps and τ2′ = 0.70 ± 0.10 ps, close to the absorption results. Based on the temporal evolution of the transient spectra, especially the “fast” excited-state absorption band at λ ≈ 570 nm, and on the global kinetic analysis of the time profiles, τ1 is assigned to an ultrafast transformation of the optically excited ππ* state to an intermediate state, which may be the nπ* state, τ2 to the subsequent isomerisation and radiationless deactivation time to the S0 electronic ground state, and τ3 to the eventual vibrational cooling of the internally “hot” S0 molecules.

Graphical abstract: Sequential photoisomerisation dynamics of the push–pull azobenzene Disperse Red 1

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Publication details

The article was received on 08 Dec 2011, accepted on 22 Mar 2012 and first published on 19 Apr 2012


Article type: Paper
DOI: 10.1039/C2PP05400K
Citation: Photochem. Photobiol. Sci., 2012,11, 1210-1219
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    Sequential photoisomerisation dynamics of the push–pull azobenzene Disperse Red 1

    J. Bahrenburg, K. Röttger, R. Siewertsen, F. Renth and F. Temps, Photochem. Photobiol. Sci., 2012, 11, 1210
    DOI: 10.1039/C2PP05400K

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