Hydrophobic effects on photophysical and photochemical processes: 1. Aggregation and excimer formation of alkyl β-naphthoates with long chain in poor solvents

The fluorescence spectra of alkyl β-naphthoates with various chain lengths (A_n) in DMSO-H₂O and ethylene glycol-water (EG-H₂O) mixtures were studied. The β-naphthoates with short chain show monomer fluorescence only in both solvent mixtures, while fluorescence spectra of long chain alkyl β-naphthoates are dominated by excimer emission. Addition of long chain hydrocarbon or amylose resulted in the reduction of excimer emission and enhancement of monomer fluorescence. All these experimental results supported intermolecular aggregation of long chain alkyl β-naphthoates in poor solvents. The kinetic parameters of the formation and dissociation of excimer as well as fluorescence polarization in aggregates were measured. These data provided an insight into the characteristics of aggregates.