MULTIDIMENSIONAL PHOTOCHEMISTRY IN 4-(N,N-DIMETHYLAMINO) STILBENE

The absorption and fluorescence properties, quantum yields and lifetimes of fluorescence observed for several selectively bridged 4-dimethylaminostilbene (DS) derivatives are shown to reflect different pathways for singlet state relaxation. The single bond connecting the dialkylanilino group to the ethylene group (bond 2) is the site of decoupling between the donor and acceptor parts to form a TICT excited state. AM1 and CNDO/S calculations have been used to interpret the multidimensional photochemistry of DS. The potential energy curves, dipole moments, oscillator strengths and atomic charge densities have been calculated for different twist angles around the single bond 2 and the solvent-induced changes have been considered for the four lowest excited states. By bridging the single bond 2 chemically, dimensionality is reduced, and only one product state, the phantom singlet state P*, remains. For this channel, the measurements of fluorescence quantum yields and lifetimes versus temperature indicate a higher activation energy in ethanol than in diethylether.