Formation Enthalpy of Exciplexes with Partial Charge Transfer as a Function of the Electron-Transfer Driving Force

The dependence of the formation enthalpy ()H_Ex* and the Gibbs energy (G_Ex*) of exciplexes with partial charge transfer on the Gibbs energy of electron transfer G_et*, the parameters of the electronic structure of an exciplex (the difference in the energies of the charge transfer (CT) state and a locally excited state (LE) in a vacuum ( H₂₂⁰– H₁₁⁰), the matrix element of the electronic coupling of the CT and LE states H₁₂, the dipole moment of the CT state, and the repulsion energy in an exciplex a"), and the polarity of the medium was analyzed. The consideration of the repulsion energy in the exciplex is necessary for correlation of the experimental values of H_Ex* and the spectral shift of the exciplex emission with respect to the LE state. All of these parameters depend on the particular nature of the exciplex, which is the reason for the lack of the general dependence of H_Ex* and G_Ex* on G_et* for exciplexes with partial charge transfer.