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

The fluorescence properties of polymethylene bis‐β‐naphthoates with various chain lengths (B n ) in poor solvents such as dimethyl sulfoxide‐water (DMSO–H 2 O) and ethylene glycol‐water(EG–H 2 O) were measured under stationary and nonstationary conditions at various temperatures. Hydrophobic interactions bring the two chromophores of B 3 , B 4 and B 10 into sandwich arrangement in ground state, thus promote intramolecular excimer formation upon excitation. The perfect overlapping structure of B 2 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 B 2 is the structure in which the two naphthyl rings are in proximity. The activation energy, enthalpy and entropy changes of excimer formation of B 2 were calculated from the fluorescence decay parameters.