Quenching by dimethylmercury of 1,2-benzanthracene fluorescence via an exciplex

Abstract

The fluorescence quenching of 1,2-benzanthracene by dimethylmercury has been investigated in various solvents. In benzene and toluene a modification of the emission spectrum recorded in the presence of the organometallic molecule arises from the superposition of a 1,2-benzanthracene-dimethylmercury exciplex emission on the unmodified aromatic molecule fluorescence. This interpretation is strengthened by the examination at different temperatures of the fluorescence emission of the aromatic molecule in neat dimethylmercury.

Temperature effects on the rate constant of fluorescence quenching indicate that the enthalpy of formation of the excited complex is small and solvent independent: ΔH^°_f(toluene)= 1.3 kcal mol^–1ΔH^°_f(benzene)= 1.2 kcal mol^–1ΔH^°_f(ethyl acetate)= 1.2 kcal mol^–1ΔH^°_f(acetonitrile)= 1.4 kcal mol^–1ΔH^°_f(ethanol)= 1.8 kcal mol^–1.

A ΔH^°_f(dimethylmercury) value of 1.4 kcal mol^–1 was obtained by measuring the ratio of the fluorescence intensities of the two species in equilibrium as a function of the temperature.