(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 (ϕF) and lifetimes (τF) together with the triplet quantum yields (ϕT) and the spectral and kinetic characteristics of T1 were measured in methylcyclohexane and acetonitrile. The S1 decay parameters (ϕF, τF, ϕT) 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 (ϕPI) 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.