Emission from aromatic hydrocarbon-diene and -olefin exciplexes

Luminescence from aromatic hydrocarbon-olefin and -diene exciplexes, providing strong evidence for their intermediary in singlet quenching processes, is reported. Solvent dependence of the emission maximum gives a value of 10.8D for the dipole moment of the 1-cyanonaphthalene-1,2-dimethylcyclopentene exciplex while the temperature dependence affords a value of 6.7 kcal/M for the heat of formation. Linear-free-energy correlations of rate constants for 1-cyanonaphthalene and naphthalene fluorescence quenching by dienes and olefins and strained hydrocarbons with the adiabatic ionization potentials of the quenchers are consistent with major contributions from charge-resonance in the exciplex formation process.