Formation enthalpy and entropy of exciplexes with variable extent of charge transfer in solvents of different polarity

Temperature dependence was studied for relative quantum yields of emission from some exciplexes of pyrene, 1,12-benzoperylene, and 9-cyanoanthracene w ith methoxybenzenes or methylnaphthalenes in solvents of different polarity (ranging from toluene to acetonitrile). The enthalpy DeltaH*(Ex), the entr opy DeltaS*(Ex), and the Gibbs free energy DeltaG*(Ex) of formation of the exciplexes were determined. Depending of the Gibbs free energy of excited-s tate electron transfer (DeltaG*(et)) and solvent polarity, the values of De ltaH*(Ex), DeltaS*(Ex), and DeltaG*(Ex) vary over the ranges from -5 to -40 0 mol(-1), from +3 to -90 J mol(-1) K-1, and from +3 to -21 kJ mol(-1), re spectively. The possibility is discussed that the effect of solvent polarit y DeltaG*(et) on the exciplex formation enthalpies can be rationalized in t erms of the model of correlated polarization of an exciplex and the medium.