Photophysics of 1-dimethylaminonaphthalene in aqueous-organic binary solvents

Fluorescence and absorption spectra of 1-dimethylaminonaphthalene (DMAN) in aqueous-organic binary solvents were recorded as a function of the content of organic components (methanol, ethanol, n- and i-propanol, and acetonitrile) for the purpose of understanding the photophysics of DMAN. Whereas the absorption spectra underwent minor change with increasing organic component, the fluorescence spectra experienced a continuous blue-shift in the band position and the fluorescence quantum yield increased reaching a maximum before continuous decrease. It was found that, in a series of aqueous-organic binary solvents, the variations of the quantum yield versus solvent polarity turned at nearly the same solvent polarity equivalent to an E-T(30) value of ca. 57 kcal mol(-1). It is hence suggested that while the emissive state is intramolecular charge transfer in nature, the radiationless decay channel is solvent-polarity dependent. (C) 2000 Elsevier Science B.V. All rights reserved.