SPECTROSCOPY AND DYNAMICS OF JET-COOLED 4-DIMETHYLAMINO-4'-CYANO STILBENE IN THE S-1 STATE

The S-1 state of jet-cooled 4-(N,N-dimethylamino)-4'-cyanostilbene (DCS) was studied by picosecond fluorescence spectroscopy. The line structure of the S-0 --> S-1-excitation spectrum is a superposition of transitions characteristic of isolated trans-stilbene and the dimethylamino group. Rotational contour analysis and rotational coherence spectroscopy suggest a non-planar geometry of DCS in both electronic states. Fluorescence decays are monoexponential up to 3700 cm(-1) above the origin at 27038 cm(-1). The lifetimes vary little up to 733 cm(-1) ([tau] = 2.097 ns) and start to decrease above this energy because of the onset of photoisomerization. An RRKM-fit to the non-radiative rate coefficients yields a barrier height E(0) = 745 cm(-1).