Studies on Conservation of Spin-Polarization in Hydrogen Atom Transfer Reactions.

利用时间分辨ESR技术获得了三重态的分子常数，并阐明了系统间交叉、三重态-三重态能量传递、氢原子转移反应等机理。得到的主要结果总结如下：(1)双乙酰基<^3n(pi)^*>态：从双乙酰基<T_1> <- <S_0>吸收直接产生的<^3n(pi)^*>态的自旋极化ESR信号，确定D值的符号为正。在乙醇和非极性溶剂中，<^3n(pi)^*>状态下，显著的基质效应对自旋极化的影响可以通过系统间交叉通道的切换来解释。(2)三重态-三重态能量转移：研究了77 K下有机基质中三重态能量转移引起的瞬态自旋极化ESR谱。光敏产生的受体三重态的自旋极化ESR光谱与直接光激发产生的ESR光谱完全不同。实验结果表明，在三态-三态能量转移过程中，给体的自旋极化转移给了受体，并且Zeeman量子数守恒，这可以用交换机制来解释。(3)三重态-双重态体系中的自旋极化转移：研究了溶液中三重态分子与氮氧化物自由基的相互作用。自由基中诱导的自旋极化反映了作为相遇伙伴的三重态分子的自旋极化。在氮氧自由基中观察到的自旋极化ESR信号可以用电子和/或自旋交换机制来解释。(4)三态苄基的自旋极化逆转：在苯溶液中，通过苯胺、酚类等给体体系的光照射，观察了产生自由基的CIDEP信号。随着给体浓度和苄基浓度以及给体反应活性的改变，CIDEP信号的极性发生了逆转。自旋极化的反转可以解释为苯基分子之间的三重态能量转移以及苯基从非平面到平面的结构变化。少

The time-resolved ESR technique was applied to obtain molecular constants of triplet states and to elucidate mechanisms of intersystem crossing, triplet-triplet energy transfer, hydrogen atom transfer reaction and etc. Main results obtained are summarized as follows:(1) The <^3n(pi)^*> state of biacetyl: From the spin-polarized ESR signals of the <^3n(pi)^*> state of biacetyl produced directly by the <T_1> <- <S_0> absorption, the sign of the D value is determined to be positive. The marked matrix effect on spin polarization in the <^3n(pi)^*> state is interpreted by the switching of intersystem crossing channel in ethanol and nonpolar solvents.(2) Triplet-triplet energy transfer: Transient spin-polarized ESR spectra of triplet state resulting from triplet-triplet energy transfer were studied in organic matrices at 77 K. The spin-polarized ESR spectra of the acceptor triplet produced by the photosensitization were completely different from those of direct photoexcitation. It is conclud … More ed that the spin polarization of the donor is transferred to the acceptor by triplet-triplet energy transfer and the Zeeman quantum number is conserved, which is interpreted by the exchange mechanism.(3) Spin-polarization transfer in the triplet-doublet system: The interaction between triplet molecules and nitroxide radicals was studied in solution. Spin polarization induced in the radical reflects that of the triplet molecule which is an encounter partner. The spin-polarized ESR signals observed in nitroxide radicals are interpreted in terms of the electron and/or spin exchange mechanisms.(4) Reversal of spin-polarization in the triplet benzyl: The CIDEP signals of produced radicals were observed by the photoirradiation of the benzyl-hydrogen atom donor (aniline, phenoles) systems in benzen solusion. The polarities of the CIDEP signals were reversed by the change of donor and benzyl concentrations and donor reactivities. The revers of spin-polrization was interpreted in terms of the triplet energy transfer between benzyl molecules followed by the structure change of benzyl from nonplanar to planar. Less