Triplet and radical ion properties of styrylnaphthalenes and their aza-derivatives: a laser flash photolytic study
作者:Gian Gaetano Aloisi、Fausto Elisei、Loredana Latterini
DOI:10.1039/ft9928802139
日期:——
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 (λexc= 308 and 347 nm), T1→ Tn absorption was undetectable and DAE˙+ was the only transient observed, even though it was produced in low yield (ϕPI⩽ 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.
激光闪光光解技术被用于生成和研究一些二芳基乙烯(DAE)的最低激发三重态(T1)和自由基离子(DAE˙+ 和 DAE˙–)。特别研究了两种反式芪基萘异构体(n-StN,其中n为萘上的1或2)和四种反式1-(n-萘基)-2-(n'-吡啶基)乙烯(n,n'-NPE,其中n,n'分别为1,4';2,2';2,3'和2,4')。通过吸收光谱、衰减动力学、摩尔吸收系数(对于DAE˙+ 和 DAE˙–)和生成量子产率(对于T1和DAE˙+)来表征这些瞬态物质。除了1-StN,在无猝灭剂的直接激发下(激发波长为308和347 nm),T1→ Tn吸收无法检测到,且DAE˙+是唯一观察到的瞬态,尽管其生成产率很低(ϕPI⩽ 0.06)。在含有4-溴-N,N-二甲基苯胺(BrDMA)的正己烷中,BrDMA增强了系间窜越量子产率,从而表征了DAEs的T1三重态;而在乙腈中,在二乙基苯胺(DEA)和BrDMA的存在下,通过347 nm的激光激发生成了DAE˙–并进行了研究。