Bahrenburg, J., Rottger, K., Siewertsen, R., Renth, F. and Temps, Friedrich (2012) Sequential photoisomerisation dynamics of the push-pull azobenzene Disperse Red 1. Photochemical & Photobiological Sciences, 11 (7). pp. 1210-1219.

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Abstract

The ultrafast dynamics of the push-pull azobenzene Disperse Red 1 following photoexcitation at lambda(pump) = 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 lambda approximate to 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, tau(1) = 0.08 +/- 0.03 ps, tau(2) = 0.99 +/- 0.02 ps, and tau(3) = 6.0 +/- 0.1 ps. Fluorescence-time profiles were biexponential with time constants tau(1)' = 0.12 +/- 0.06 ps and tau(2)' = 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 lambda approximate to 570 nm, and on the global kinetic analysis of the time profiles, tau(1) is assigned to an ultrafast transformation of the optically excited pi pi* state to an intermediate state, which may be the n pi* state, tau(2) to the subsequent isomerisation and radiationless deactivation time to the S-0 electronic ground state, and tau(3) to the eventual vibrational cooling of the internally "hot" S-0 molecules.

Document Type:	Article
Additional Information:	Univ Kiel, Inst Phys Chem, D-24098 Kiel, Germany. Renth, F (reprint author), Univ Kiel, Inst Phys Chem, Olshausenstr 40, D-24098 Kiel, Germany. renth@phc.uni-kiel.de; temps@phc.uni-kiel.de
Keywords:	transient absorption-spectroscopy up-conversion spectroscopy femtosecond fluorescence solvent dynamics excited-state s-1 state ab-initio isomerization derivatives excitation
Research affiliation:	Kiel University OceanRep > The Future Ocean - Cluster of Excellence
Projects:	Future Ocean
Date Deposited:	14 May 2014 10:24
Last Modified:	14 May 2014 10:24
URI:	https://oceanrep.geomar.de/id/eprint/23803

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