Dipole moments of electronically excited states of 4-N,N-dimethylaminobenzonitrile and related compounds deduced from transient dielectric losses

Abstract

A reinvestigation is reported of UV-laser-induced transient dielectric losses at microwave frequencies in solutions of 4-N, N-dimethylaminobenzonitrile (DMABN) and related compounds in cyclohexane and 1,5-dioxane and of 9,9'-bianthryl in n-hexane. Excitation of DMABN and related compounds in cyclohexane may produce mobile electrons. This does not happen with 9,9'-bianthryl in n-hexane or with solutions in 1,4-dioxane. Dipole moments of the first excited singlet state of DMABN and related compounds, determined previously from transient dielectric losses, need to be corrected. The corrected dipole moments are obtained by eliminating the contribution of the mobile electrons to the dielectric loss by saturating the solution with CO 2 which acts as a scavenger. The corrections amount to as much as 30-45% of the previously reported values. Previous conclusions concerning twisted solute—solvent exciplexes remain unaffected. No evidence is found for the existence of planar solute—solvent exciplexes.