title: Characterization of trans-2-[4-[(dimethylamino)styryl]benzothiazole as an ultrafast isomerization probe and a modifed Kramers theory analysis.
abstract: The photophysics of trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) was investigated by electronic structure calculations and steady-state and time-resolved emission spectroscopy in a wide range of solvents, including temperature and pressure dependence. DMASBT undergoes a facile photoinduced trans-cis isomerization similar to the reaction of trans-stilbene. The cis isomer has a lifetime of ∼1 ps and does not contribute appreciably to the steady-state emission spectrum. The absorption spectrum of the cis form overlaps that of the trans form such that considerable care is needed in determining correct emission quantum yields. The approximate equality of absorption and emission transition moments of DMASBT in all solvents indicates that absorption and emission involve a single excited state with high radiative rate. The low quantum yields of DMASBT in low-viscosity solvents reflect emission lifetimes in the 20-50 ps range. The nonradiative rates of DMASBT, which are assumed to measure the rate of isomerization in S1, depend upon both solvent viscosity and polarity. A modified Kramers analysis, which allows for a polarity-dependent barrier height, provides a satisfactory description of these rates but only if it is assumed that friction in alcohol solvents is more weakly dependent upon viscosity than in other types of solvents.
authors.affiliation: Department of Chemistry, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Minako
authors.initials: M
authors.lastname: Kondo
authors.forename: Xiang
authors.initials: X
authors.lastname: Li
authors.forename: Mark
authors.initials: M
authors.lastname: Maroncelli