STYRENE AMINE EXCIPLEXES - SUBSTITUENT EFFECTS

The reductive and oxidative quenching of para-substituted styrenes 1-8 by amine and olefin were studied in polar and non-polar solvents. Fluorescent exciplexes were observed in non-polar solvent (n-hexane) from the quenching of styrenes 1-8 with triethylamine, dimethylbutylamine, diisopropylethylamine and diisopropylmethylamine. The maximum fluorescent energies were well correlated with the Rehm-Weller theoretical values with the exception of those with a small enthalpy of dissociation for the exciplexes. There was also systematic correlation between the exciplex fluorescence maximum energies and the Hammett sigma(p) constants. There were no obvious substituent effects on the exciplex dipole moments. A simple frontier molecular orbital theory was applied to explain the linear correlation between exciplex formation and emission. The effects of electron transfer, exciplex formation, orbital interaction and solvent on the quenching mechanism were also examined.