Evidence for 1La, 1Lb Dual State Emission in 1-naphthol and 1-methoxynaphthalene Fluorescence in Liquid Solutions Academic Article uri icon

abstract

  • The steady-state fluorescence spectra of 1-methoxynaphthalene and 1-naphthol were measured in pure organic solvents and in binary mixtures of water and several organic solvents. The 1-isomers exhibited a much larger fluorescence Stokes-shift than the corresponding 2-isomers. The emission spectra of 1-methoxynaphthalene and 1-naphthol in pure nonpolar organic solvents exhibited roughly the same structured spectral features, while the fluorescence spectra in water and formamide exhibited much broader red-shifted and less structured spectral features. In accord with previous observations, we attribute these spectral changes to two emitting states, 1Lb and 1La, whose relative fluorescence intensities are sensitive to solvent polarity. Our analysis of the fluorescence spectra of 1-naphthol and 1-methoxynaphthalene by Pekarian functions have demonstrated that the 1La state becomes the dominant emitting state in polar solvents. In addition, the 1La state was found to be further stabilized in hydrogen-bond-donating solvents. In contrast to previous suggestions, the onset of the excited-state proton transfer reaction from 1-naphthol occurred at higher solvent polarities than those required for the establishment of a dominantly 1La emitting state.

publication date

  • January 1, 1999