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

The photophysical behaviour of the lowest singlet (S-1) and triplet (T-1) excited states of some (E)-9-styrylanthracene derivatives (StAns) has been studied by steady-state and pulsed techniques. Fluorescence quantum yields (phi(F)) and lifetimes (tau(F)) together with the triplet quantum yields (phi(T)) and the spectral and kinetic characteristics of T-1 were measured in methylcyclohexane and acetonitrile. The S-1 decay parameters (phi(F), tau(F), phi(T)) were found to be markedly solvent dependent when an electron-donating (NH2) or -accepting (NO2) substituent, which gives rise to lowest S-1 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 (phi(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.