In the picosecond time regime, the lowest excited singlet state of a 1,4-hexyl-bridged anthraquinone (CyAQ) undergoes intramolecular hydrogen-atom transfer giving rise to the formation of the ground-state singlet biradical (1BR) and its methide (MT, i.e. 1,4-hexylidene-bridged 9-hydroxyanthracen-10-one) which exist in equilibrium. The lowest excited triplet state of CyAQ also undergoes intramolecular hydrogen-atom transfer in the submicrosecond time regime. Intersystem crossing from the excited triplet biradical to 1BR is followed by rapid 1BR → MT conversion to reach equilibrium. Although both 1BR and MT produced at 77–140 K are stable, 1BR (and/or MT) produced at room temperature changes to a 1,4-hexylidene-bridged anthraquinone (product 1) in aprotic solvents such as benzene, toluene, methylcyclohexane and 2-methyltetrahydrofuran, or to product 1 (minor) and a 1,4-hexyl-bridged 1,4-diethoxy-9,10-dihydroxyanthracene (product 2, major) in ethanol and EPA (diethyl ether–isopentane–ethanol, 5:5:2 volume ratio). Also, the interconversion of products 1 ⇌ 2 caused by the change of an aprotic solvent ⇌ ethanol (or EPA) and the slow thermal reversion of products 1 and 2 to the original anthraquinone (CyAQ) can be seen at room temperature.
在皮秒时间体系中,1,4-己基桥联
蒽醌(CyAQ)的最低激发单线态发生分子内
氢原子转移,从而形成基态单线双拉德态(1BR)及其甲
酰胺态(
MT,即 1,4-亚己基桥联
9-羟基蒽-10-
酮),两者处于平衡状态。CyAQ 的最低激发三重态也会在亚微秒时间内发生分子内
氢原子转移。从激发的三重双拉德态到 1BR 的系统间转换之后,1BR →
MT 的转换迅速达到平衡。虽然在 77-140 K 下生成的 1BR 和
MT 都很稳定,但在室温下生成的 1BR(和/或
MT)在
苯、
甲苯、
甲基环己烷和
甲基丙烯酸甲酯等非沸腾溶剂中会转变为 1,4-亚己基桥接的
蒽醌(产物 1)、或在
乙醇和 EPA(二
乙醚-
异戊烷-
乙醇,体积比为 5:体积比为 5:5:2)。此外,在室温下,还可以看到由于改变无反应溶剂⇌
乙醇(或 EPA)而引起的产物 1 ⇌ 2 的相互转化,以及产物 1 和 2 缓慢热还原为原始
蒽醌 (CyAQ)。