Formation and Anomalous Behavior of Aminonaphthalene−Cinnamonitrile Exciplexes

Abstract

The solvent dependence of the electronic spectra of several 1-aminonaphthalenes and 2-aminonaphthalenes in the absence and presence of two styrene derivatives, cinnamonitrile and 1-phenylpropene, has been investigated. The absorption maxima of the aminonaphthalenes are dependent upon both the polarity and hydrogen-bond donor and acceptor properties of the solvent and display both red and blue solvent shifts. The fluorescence maxima are more sensitive to solvent polarity than are the absorption maxima and display red shifts in both non-hydroxylic and hydroxylic solvents. The excited state dipole moments of the 1-aminonaphthalenes are larger than those of the 2-aminonaphthalenes. Quenching of the aminonaphthalene fluorescence by cinnamonitrile occurs with diffusion-controlled rates in all solvents, in accord with the occurrence of exergonic electron transfer. Exciplex fluorescence is observed only for the tertiary aminonaphthalenes in nonpolar solvents. The exciplex fluorescence displays anomalous temperature dependence in hexane solution, an increase in temperature resulting in blue-shifted exciplex fluorescence and an increase in the exciplex decay time. Quenching of the aminonaphthalene fluorescence by 1-phenylpropene is slower than diffusion-controlled and is not accompanied by exciplex fluorescence.