FACTORS AFFECTING SOLVENT SHIFTS OF N-]PI] BAND OF BENZOPHENONE

The structure of the n → π* absorption band of benzophenone dissolved in alkane and alcoholic solvents was investigated throughout the temperature range of -190 to +25°C. A study of the temperature dependence of vibronic peak frequencies permitted the resolution of the solvent shift of the absorption maximum into shifts due to the overlapping π → π* band and shifts arising from the effect of hydrogen bonding on the energy of the n → π* transition. The results of this study coupled with thermodynamic data taken from the literature show that the energy of hydrogen bonding between benzophenone in its first excited singlet state and the alcoholic solvent is greater than 1 kcal/mole. No evidence was found to support the theory that the magnitude of the solvent shift of the n → π* absorption maximum could in any way be directly related to energy to hydrogen bond formation between the alcoholic solvent and benzophenone in its ground electronic state. © 1969.