Photophysical properties of diphenylacetylene derivatives in solution phase .4. N,N-dimethylanilino(phenyl)acetylene in n-hexane

By using picosecond transient absorption and fluorescence lifetime measurement techniques, we have investigated the photophysical properties of N,N-dimethylanilino(phenyl)-acetylene in n-hexane solution. The lifetime of the second excited singlet state was determined to be about 20 ps at room temperature and a strong delayed S-2 fluorescence excited from S-1 was observed. The characteristic features we observed seem to result from the accidental degeneracy of S-2 and S-1. Introduction of the dimethylamino group makes the vibrational level density high and results in a large rate constant of internal conversion from S-2 to S-1 without excess vibrational energy.