Contributions from dipolar electronically excited molecules and mobile charge carriers to photoinduced transient dielectric loss of solutions of some aniline derivatives

Abstract

UV laser excitation of a solution of N,N-dimethylaniline (DMA) in cyclohexane may cause a transient dielectric loss due to the dipoles of the lowest excited singlet (S 1) and triplet (T 0) state molecules and due to free electrons produced via two-photon absorption. In the case of N,N,N′,N′ -tetramethyl-para-phenylenediamine (TMPD) the yield of free electrons is four times larger, under the same conditions, than in the case of DMA. The consequences of photoionization for the evaluation of dipole moments of excited solutes is discussed. The contribution of free electrons to the transient dielectric loss can be eliminated efficiently by scavenging the electrons with CO 2. From the remaining contribution the dipole moments of the molecules in S 1 and T 0 are determined. In the case of DMA the values 5.0 D for S 1 and 3.2 D for T 0 are obtained.