Quantum yields (Φ) were determined for benzophenone-sensitized and direct photolysis of the title hydroxylamine (NT). Analysis of linear Stern-Volmer plots of the reciprocal of Φ against the reciprocal of NT concentration reveals that the sensitized decomposition of NT takes place via its first triplet excited state (T1) produced by triplet-triplet energy transfer from benzophenone to NT. The fact that the quantum yields for the direct photolysis are independent of NT concentration indicates no occurrence of both self-quenching and induced decomposition of NT by the photochemically generated radicals. Closer examination of the micellar and solvent viscosity effects on the quantum yields for the direct photolysis with 313-nm light shows the existence of at least two spin-correlated (singlet) radical pairs: One is a contact radical pair whose recombination eventually yields 1,3-toluoyloxyl-migrated product and the other a solvent-separated radical pair from which 1,5-toluoyloxyl-migrated product is derived in competition with diffusive escape from the solvent or micelle cage. Exclusive occurrence of the direct photolysis from the first singlet excited state (S1) was explained on the basis of the large energy gap between S1 and T1 (31 kcal mol−1) which is likely to make intersystem crossing from S1 to T1 very inefficient.
测定了
二苯甲酮敏化和直接光解标题
羟胺(NT)的量子产率(Φ)。通过分析 Φ 的倒数与 NT 浓度倒数的线性 Stern-Volmer 图,可以发现 NT 的敏化分解是通过其第一个三重激发态(T1)进行的,该激发态是通过三重三重能从
二苯甲酮转移到 NT 而产生的。直接光解的量子产率与 NT 浓度无关,这一事实表明,光
化学产生的自由基不会对 NT 产生自淬和诱导分解作用。仔细研究胶束和溶剂粘度对 313 纳米光直接光解量子产率的影响,可以发现至少存在两个自旋相关(单子)自由基对:一个是接触自由基对,其
重组最终产生 1,3-
甲苯甲酰基迁移产物;另一个是溶剂分离自由基对,1,5-
甲苯甲酰基迁移产物在溶剂或胶束笼的扩散逃逸竞争中产生。S1 和 T1 之间的能量差距很大(31 kcal mol-1),这可能会导致从 S1 到 T1 的系统间交叉效率很低,因此可以解释为什么从第一个单激发态(S1)会发生直接光解。