Spectroscopy and dynamics of jet-cooled 4-dimethylamino-4′-cyanostilbene in the S1 state

The S1 state of jet-cooled 4-(N,N-dimethylamino)-4′-cyanostilbene (DCS) was studied by picosecond fluorescence spectroscopy. The line structure of the S0 → S1-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 (〈τ〉 = 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 E0 = 745 cm−1.