(E)-9-STYRYLANTHRACENE DERIVATIVES AND THEIR INTERACTIONS WITH ELECTRON-DONORS AND ACCEPTORS - FLUOROMETRIC 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 q uantum yields (phi(F)) and lifetimes (tau(F)) together with the triple t quantum yields (phi(T)) and the spectral and kinetic characteristics of T-1 were measured in methylcyclohexane and acetonitrile. The S-1 d ecay parameters (phi(F), tau(F), phi(T)) were found to be markedly sol vent dependent when an electron-donating (NH2) or -accepting (NO2) sub stituent, which gives rise to lowest S-1 states with charge-transfer c haracter, is present. N,N-Diethylaniline (DEA) and 4-bromo-N,N-dimethy laniline efficiently quench StAn fluorescence; DEA, in non-polar solve nts, forms exciplexes which were characterised by fluorescence spectra and lifetime measurements. In acetonitrile, StAns undergo photoionisa tion with low quantum yield (phi(PI)) to give the corresponding radica l cation (StAn(.+)). The concentration of StAn(.+) was enhanced by add ing an electron acceptor (i.e. 1,4-dicyanobenzene) or by sensitizing t he electron-transfer process from StAn with chloranil or with the dicy anoanthracene-biphenyl (DCA-Bp) system. In the same solvent, the quenc hing by DEA produces the radical anion StAn(.-). The radical ions of t he StAns were characterised in terms of absorption spectra, molar abso rption coefficients, half-lives and formation quantum yields.