Abstract
The role of polar solvent in determining the photophysics of normal (b*) and anomalous (a*) fluorescence from 4-N,N-dimethylaminobenzonitrile (DMABN) and related compounds has been investigated by means of picosecond time-resolved fluorescence studies in non-polar/polar solvent mixtures, and by electronic spectroscopic studies on complexes of 1:1 stoichiometry prepared by nozzle expansion. The solution phase results indicate clearly that a DMABN-polar solvent complex is formed initially in either ground or excited state, and that this rearranges to a geometry from which the b* to a* state transition can occur. Specific solvent-solute interactions are clearly indicated by this work, and these lead to the necessity of modelling b* state decay kinetics in solution by a distribution of decay times.Laser induced fluorescence studies of jet-cooled solvated complexes of DMABN and the related molecule 4-aminobenzonitrile (4-ABN) provide evidence for the existence of 1:1 complexes involving interaction of a protic solvent molecule with either the cyano group or the amino group. In the case of 4-ABN both types of complex are fluorescent whereas in the case of DMABN, those complexes involving interaction with the dimethylamino group appear to be non-emissive. This behaviour may be due to formation of DMABN-solvent exciplex which constitutes a dark state under jet-cooled conditions. Neither the DMABN bare molecule nor the observed 1:1 solvated complexes exhibit a* emission in the jet.