Temperature dependence of the luminescence of 2-aminophenyl phenylsulphone in polar solvents

Abstract

After light excitation, 2-aminophenyl phenylsulphone has been found to fluoresce strongly in polar solvents (ϕ_f= 0.20 in aerated propionitrile solution, room temperature). The dependence of the absorption and emission spectra on solvent polarity has shown that the excited state involved in the lowest-energy absorption which is responsible for the emission is of charge-transfer nature with moderate charge delocalization (µ≈ 6.5 D from emission measurements). The temperature dependence of the emission lifetime and emission spectrum has been obtained for the temperature range 293–90 K in propionitrile-butyronitrile (4 : 5 v/v) solution. While the emission intensity increases monotonically from room temperature to 90 K, ϕ_f= 0.27 to 0.54, respectively, the lifetime increases from room temperature (τ_f= 6.5 ns) to 150 K (τ_f= 10.6 ns), but decreases on further lowering the temperature (τ_f= 8.3 ns at 90 K). This complicated behaviour is explained in terms of solute–solvent polar interactions and by taking into account the freezing of the solvent for T < 150 K.