(E)-9-styrylanthracene derivatives and their interactions with electron donors and acceptors. Fluorimetric and flash photolytic studies

Abstract

The photophysical behaviour of the lowest singlet (S₁) and triplet (T₁) excited states of some (E)-9-styrylanthracene derivatives (StAns) has been studied by steady-state and pulsed techniques. Fluorescence quantum yields (ϕ_F) and lifetimes (τ_F) together with the triplet quantum yields (ϕ_T) and the spectral and kinetic characteristics of T₁ were measured in methylcyclohexane and acetonitrile. The S₁ decay parameters (ϕ_F, τ_F, ϕ_T) were found to be markedly solvent dependent when an electron-donating (NH₂) or -accepting (NO₂) substituent, which gives rise to lowest S₁ states with charge-transfer character, is present. N,N-Diethylaniline (DEA) and 4-bromo-N,N-dimethylaniline efficiently quench StAn fluorescence; DEA, in non-polar solvents, forms exciplexes which were characterised by fluorescence spectra and lifetime measurements. In acetonitrile, StAns undergo photoionisation with low quantum yield (ϕ_PI) to give the corresponding radical cation (StAn˙⁺). The concentration of StAn˙⁺ was enhanced by adding an electron acceptor (i.e. 1,4-dicyanobenzene) or by sensitizing the electron-transfer process from StAn with chloranil or with the dicyanoanthracene–biphenyl (DCA–Bp) system. In the same solvent, the quenching by DEA produces the radical anion StAn˙^–. The radical ions of the StAns were characterised in terms of absorption spectra, molar absorption coefficients, half-lives and formation quantum yields.