Photo-Induced Intermolecular Electron Transfer from Donating Amines to Accepting Diarylethylenes in Different Solvents

Abstract

The fluorescence quenching of newly synthesized diarylethylenes by some aliphatic and aromatic amines has been carried out at room temperature in solvents of various polarities and viscosities including acetonitrile, methanol, ethanol, and cyclohexane using steady-state measurements. Additionally, the cyclic voltammetric behavior of the investigated diarylethylenes has been studied, in order to determine their reduction potentials, which are necessary for calculation the Gibbs energy change for the photoinduced, electron transfer (ET) reactions in diarylethylene–amine systems. No change in the shape of the fluorescence spectra was observed, except for diarylethylenes–N,N-dimethyl aniline pairs in cyclohexane at which an exciplex was observed. The quenching mechanism is due to the ET from the ground state amines to the excited diarylethylenes. Both linear and non-linear Stern–Volmer behaviors have been encountered. The observed k q values for different diarylethylenes–amine pairs do not correlate with the basicity (pK b) of the amines but decrease with increasing the oxidation potentials of the amines. The bimolecular quenching rate constants have been correlated with ∆G° values for the ET reactions according to the Marcus outer-sphere ET theory.