Hydrophobic effects on photophysical and photochemical processes: 4. The conformation of polymethylene bis-β-naphthoates in poor solvents and their intramolecular excimer

Abstract

The fluorescence properties of polymethylene bis-β-naphthoates with various chain lengths (Bn) in poor solvents such as dimethyl sulfoxide-water (DMSO–H2O) and ethylene glycol-water(EG–H2O) were measured under stationary and nonstationary conditions at various temperatures. Hydrophobic interactions bring the two chromophores of B3, B4 and B10 into sandwich arrangement in ground state, thus promote intramolecular excimer formation upon excitation. The perfect overlapping structure of B2 can not be formed in ground state because of the eclipsed conformation of two methylene groups in such a sandwich arrangement. The favorable conformation of B2 is the structure in which the two naphthyl rings are in proximity. The activation energy, enthalpy and entropy changes of excimer formation of B2 were calculated from the fluorescence decay parameters.