Radiationless processes of N,N-dimethylaniline derivatives in solution. Time-resolved optoacoustic studies.

Radiationless deactivation processes of a series of N,N-dimethylaniline der ivatives in cyclohexane were studied by fluorescence and optoacoustic measu rements to reveal the effects of amino twisting on the photophysical proper ties. From the optoacoustic measurements the quantum yield of intersystem c rossing (ISC) was determined for the sample compounds, and the various rate parameters (fluorescence, internal conversion (IC), and intersystem crossi ng) were derived. For N,N-dimethylxylidine which has a pretwisted dimethyl amino group, a significant increase in the rates of IC and ISC was found, s uggesting that structural relaxation of the dimethyl amino group is respons ible for the fast radiationless processes.