‘Excimer’ fluorescence VII. Spectral studies of naphthalene and its derivatives

Abstract

The fluorescence spectra of solutions of naphthalene and fourteen of its methyl, ethyl, dimethyl and trimethyl derivatives were observed as a function of molar concentration c at 20 °C and as a function of temperature from 20 to -70 °C. All the compounds show similar excimer fluorescence characteristics with mean values of the excimer binding energy B = 0.28 ± 0.03 eV and of the excimer interaction energy V' m = 0.765 ± 0.03 eV, with the exception of 1,8-dimethyl naphthalene (B = 0.14 eV) in which excimer formation is sterically hindered. The monomer fluorescence quantum efficiencies and ionization potentials were also determined. The fluorescence spectra of liquid 1,6-dimethyl naphthalene and its solutions in three solvents were observed, and the rate parameters and the entropy change ∆ S on excimer formation were determined, B and ∆ S (= -19.1 cal mole -1 deg -1 ) have similar values in the pure liquid and in cis -decalin and dilute ( c ≤ 1 m) cyclohexane solutions, but slight differences occur in n -heptane and concentrated (c > 1 m ) cyclohexane solutions.