Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma University, Kiryu, Gunma 376-8515, Japan.
J Phys Chem A. 2009 Nov 19;113(46):12831-7. doi: 10.1021/jp9074459.
Photochemical properties of alpha-cleavage of the C-S bond in excited states of p-biphenyl thioacetate and p-biphenyl thiobenzoate (Me-SBP and Ph-SBP) in solution are investigated using steady-state and laser flash photolyses in comparison with those of S-phenyl thiobenzoate, where the photo-Fries rearrangement was reported to be absent. Although Me-SBP and Ph-SBP decompose upon 254 nm photolysis in acetonitrile irrespective of the amount of the dissolved oxygen, no definite photoproducts due to the photo-Fries rearrangement were found. Laser flash photolysis (266 nm) of these molecules reveals the occurrence of the C-S bond cleavage in the excited state based on the observation of the formation of the biphenylylthiyl radical (BTR) in the transient absorption. Quantum yields (Phi(rad)) of the BTR formation were determined to be 0.20 and 0.15 for Me-SBP and Ph-SBP, respectively. Triplet sensitization of Ph-SBP using xanthone (XT) as a sensitizer shows that the lowest triplet (T(1)) state of Ph-SBP is dissociative for the C-S bond with an efficiency of >or.56. In contrast, triplet sensitization of Me-SBP using acetone as a sensitizer demonstrates the efficient formation of triplet Me-SBP, and the molar absorption coefficient of the triplet-triplet absorption was determined. No photochemical reactions are found in the T(1) state of Me-SBP. Upon 355 nm laser flash photolysis of the T(1) state of Me-SBP, the formation of BTR is confirmed in the transient absorption. This observation indicates the C-S bond cleavage in a highly excited triplet (T(n)) state of Me-SBP. The quantum yield (Phi(dec)) of the alpha-cleavage in the T(n) state of Me-SBP was determined to be 0.69. Photochemical features of Me-SBP and Ph-SBP are discussed from the viewpoint of the spin-multiplicity of the bond dissociative states.
在溶液中，通过稳态和激光闪光光解研究了激发态下对-联苯硫代乙酸酯和对-联苯硫代苯甲酸酯（Me-SBP 和 Ph-SBP）中 C-S 键α断裂的光化学性质，并与 S-苯基硫代苯甲酸酯进行了比较，据报道后者不存在光-Fries 重排。尽管 Me-SBP 和 Ph-SBP 在乙腈中于 254nm 光解时会分解，无论溶解氧的量如何，但没有发现由于光-Fries 重排而产生的明确光产物。这些分子的激光闪光光解（266nm）基于瞬态吸收中发现的联苯硫基自由基（BTR）的形成，揭示了激发态中 C-S 键的断裂。BTR 形成的量子产率（Phi(rad)）分别为 Me-SBP 和 Ph-SBP 的 0.20 和 0.15。使用黄嘌呤（XT）作为敏化剂对 Ph-SBP 的三重态敏化表明，Ph-SBP 的最低三重态（T(1)）对于 C-S 键是离解的，效率大于或等于 0.56。相比之下，使用丙酮作为敏化剂对 Me-SBP 的三重态敏化表明了高效形成三重态 Me-SBP，并且确定了三重态-三重态吸收的摩尔吸收系数。在 Me-SBP 的 T(1)态中未发现光化学反应。在 Me-SBP 的 T(1)态于 355nm 激光闪光光解时，在瞬态吸收中确认了 BTR 的形成。这一观察表明，Me-SBP 的高度激发三重态（T(n)）中存在 C-S 键断裂。Me-SBP 的 T(n)态中α断裂的量子产率（Phi(dec)）确定为 0.69。从键离解态的自旋多重性的角度讨论了 Me-SBP 和 Ph-SBP 的光化学性质。
