Triplet and radical ion properties of styrylnaphthalenes and their aza-derivatives: a laser flash photolytic study

Abstract

Laser flash photolysis was used to produce and investigate the lowest excited triplet state (T₁) and radical ions (DAE^˙+ and DAE^˙–) of some diarylethylenes (DAE). In particular, the two trans-styrylnaphthalene isomers (n-StN, where n= 1 or 2 on the naphthalene) and four trans-1-(n-naphthyl)-2-(n′-pyridyl)ethylenes (n,n′-NPE, with n,n′= 1,4′; 2,2′; 2,3′ and 2,4′) were studied. The transients were characterized in terms of their absorption spectra, decay kinetics, molar absorption coefficients (for DAE^˙+ and DAE^˙–) and formation quantum yields (for T₁ and DAE^˙+). Except for 1-StN, under direct excitation in the absence of quenchers (λ_exc= 308 and 347 nm), T₁→ T_n absorption was undetectable and DAE^˙+ was the only transient observed, even though it was produced in low yield (ϕ_PI⩽ 0.06). The triplet state T₁ of the DAEs was characterized in n-hexane, in the presence of 4-bromo-N, N-dimethylaniline (BrDMA) which enhances the intersystem-crossing quantum yields, while DAE^˙– was produced and studied in acetonitrile, by laser excitation at 347 nm, in the presence of diethylaniline (DEA) and BrDMA.