UV irradiation (λinc= 254 nm) of 1-bromo-2,2-bis(p-methoxyphenyl)ethene (AAHVB) in acetonitrile solution results in its decomposition: ϕ(–AAHVB)= 0.18 both in the absence and presence of O2. Apart from the isomers [(E)-1-bromo-1,2-bis(p-methoxyphenyl)ethene (HAAVB) and (Z)-1-bromo-1,2-bis(p-methoxyphenyl) ethene (AHAVB)] the main photoproducts are 1,2-bis(p-methoxyphenyl)ethine (P-2) and HBr (ϕ≈ 0.1). Flash photolysis studies in acetonitrile, dichloromethane and n-hexane solution at 266 nm revealed that P-2 is formed with a halflife of less than a few ns via a singlet route involving vinyl cations which rapidly rearrange and split off protons. Part of the vinyl cations decay via a different route forming an ionic species with an optical absorption band at ca. 350 nm. The decay of the latter is not correlated with the formation of P-2. This ionic species probably results from an interaction of vinyl cations with solvent or AAHVB. AAHVB quenches triplet states of various compounds X (e.g. benzophenone, chrysene, benzil, pyrene) provided that ET(X) > 200 kJ mol–1. The energy transfer from these compounds to AAHVB does not result in the formation of P-2 or vinyl cations.
乙腈溶液中的 1-
溴-2,2-双(对
甲氧基苯基)
乙烯 (
AAHVB) 经紫外线照射 (λinc= 254 nm) 会导致其分解:在不存在 O2 和存在 O2 的情况下,φ(–
AAHVB)= 0.18 。除了异构体[(E)-1-
溴-1,2-双(对
甲氧基苯基)
乙烯(H
AAVB)和(Z)-1-
溴-1,2-双(对
甲氧基苯基)
乙烯(AHAVB) ] 主要光产物是 1,2-双(对
甲氧基苯基)
乙炔 (P-2) 和 HBr (ψ≈ 0.1)。在
乙腈、
二氯甲烷和
正己烷溶液中在 266 nm 处进行的闪光光解研究表明,P-2 是通过涉及
乙烯基阳离子的单线态途径形成的,半衰期小于几纳秒,
乙烯基阳离子快速重排并分裂出质子。部分
乙烯基阳离子通过不同的途径衰变,形成具有约 100 nm 光吸收带的离子物质。 350纳米。后者的衰变与P-2的形成无关。这种离子物质可能是
乙烯基阳离子与溶剂或
AAHVB 相互作用的结果。
AAHVB 可以猝灭各种化合物 X(例如
二苯甲酮、屈、苯偶酰、
芘)的三重态,前提是 ET(X) > 200 kJ mol–1。从这些化合物到
AAHVB 的能量转移不会导致 P-2 或
乙烯基阳离子的形成。