標題: Femtosecond fluorescence dynamics of trans-azobenzene in hexane on excitation to the S-1(n,pi*) state
作者: Lu, YC
Chang, CW
Diau, EWG
應用化學系
Department of Applied Chemistry
關鍵字: azobenzene;conical intersection;femtochemistry;up-conversion;photochromism
公開日期: 1-Oct-2002
摘要: Femtosecond fluorescence dynamics of trans-azobenzene in hexane have been investigated on excitation to the S-1(n,pi*) state at 432 nm using the up-conversion technique. Two transient components were observed to represent the fast and the slow S-1 fluorescence dynamics in the wavelength range of 550-732 nm. Based on the results obtained from recent ab initio calculations (Ishikawa, T.; Noro, T.; Shoda, T., J. Chem. Phys. 2001, 115, 7503), a dynamical picture is given in the following. Upon initial excitation to the S, state, the excited molecule is moving away from the first detection window within the observed 200-300 fs. The structural relaxation from the Franck-Condon region may be responsible for the observed fast S-1 dynamics with the driving force being the CNNC twisting motion along the rotational coordinate. For the rest of the motion on the S-1 global potential surface, the excited molecule may search for the S-0/S-1 conical intersection for an efficient internal conversion to the ground state. The nuclear motions for the observed slow S-1 dynamics not only involve the CNNC torsional coordinate but also the other degrees of freedom such as the CNN bending coordinate on the multidimensional S-1 potential energy surface. The whole electronic relaxation process occurs within the observed 1-2 ps. The slow S-1 dynamics were found to vary with the fluorescence wavelengths due to the influence of the solvent-induced vibrational relaxation in the S-1 state; the vibrational relaxation should occur on a time scale comparable to the time scale of the electronic relaxation (S-1-->S-0 internal conversion).
URI: http://hdl.handle.net/11536/28472
ISSN: 0009-4536
期刊: JOURNAL OF THE CHINESE CHEMICAL SOCIETY
Volume: 49
Issue: 5
起始頁: 693
結束頁: 701
Appears in Collections:Articles