Luminescence characteristics of 1,1'-binaphthyl- 4,4'-diol in different solvents and at various <i>p</i>H

634-638A study of absorption and fluorescence spectra of 1,1'-binaphthyl-4,4'-diol (4BNP) in solvents of different polarity and proton concentration has been carried out. Solvatochromic shifts show that the molecule is twisted in S0 state and planar in S1 state. Correlation of Stoke's shifts with solvent polarity parameters ET (30) and Bilot-Kawski (BK) values reveals that the shifts are more in accordance with ET (30) than with BK values. The neutral form of 4BNP is fluorescent only in highly acidic solution. But its fluorescence is quenched in less acidic and neutral solutions, i.e .. above pH1. The absence of neutral form fluorescence under these conditions is found to be due to diabatic quenching of fluorescence by H+ (aq). Fluorimetric titration curve of 4BNP monoanion gives a stretched sigmoidal curve with two inflection points, one at pKa* and other at pKa value.The lack of correspondence between the decrease in fluorescence intensity of the neutral form and increase in fluorescence intensity of the anion also confirms the quenching before deprotonation. The excited state acidity constants (pKa*) determined by different methods, are discussed