Effect of solvent polarity on the electronic structure and emission frequencies of exciplexes of aromatic hydrocarbons with methoxybenzenes and methylnaphthalenes

The dependence of exciplex emission spectra on the solvent polarity was stu died for exciplexes with the Gibbs free energy of excited-state electron tr ansfer, DeltaG(et)*, exceeding -0.1 eV (for pyrene, fluoranthene, 1,12-benz operylene, and 9-cyanoanthracene with methoxybenzenes or dimethyl naphthale ne). These exciplexes showed stronger changes in the spectral shift of exci plex emission and the extent of charge transfer with increasing solvent pol arity than the exciplexes having more negative DeltaG(et)* values. The para meters (difference in energy of charge transfer (CT) and locally excited (L E) states in a vacuum, (H-22(0) - H-11(0)), and the matrix element for elec tronic coupling of CT and LE states H-12 and m related to the dipole moment of the CT state and the size of the exciplex) determining the extent of ch arge transfer, the spectral shift, and other properties of exciplexes were evaluated. The parameters H-12 and m for the exciplexes examined fall in th e interval 0.1-0.5 and 1.0-1.7 eV, respectively, and the difference (H-22(0 ) - H-11(0)) is proportional to DeltaG(et)*.