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Evidence for 1 L a , 1 L b Dual State Emission in 1‐naphthol and 1‐methoxynaphthalene Fluorescence in Liquid Solutions
Author(s) -
Magnes BenZion,
Strashnikova Natalya V.,
Pines Ehud
Publication year - 1999
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.199900042
Subject(s) - chemistry , fluorescence , analytical chemistry (journal) , formamide , spectral line , excited state , emission spectrum , solvent , hydrogen bond , photochemistry , stokes shift , proton , molecule , organic chemistry , physics , quantum mechanics , astronomy , nuclear physics
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, 1 L b and 1 L a , 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 1 L a state becomes the dominant emitting state in polar solvents. In addition, the 1 L a 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 1 L a emitting state.