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

用时间分辨ESR技术测定了双乙酰的三重态的分子常数，阐明了系间交叉、三重态能量转移、氢原子转移反应等机理.主要结果如下：(1)双乙酰的&lt；^3n(Pi)^*&gt；态：从&lt；^3n(Pi)^*&gt；态的自旋极化ESR信号中确定D值的符号为正.(2)三重态能量转移：研究了77K下有机基质中三重态能量转移引起的三重态的自旋极化ESR谱。光敏化产生的受主三重态的自旋极化ESR谱与直接光激发的自旋极化谱完全不同。这是…的结论进一步指出，施主的自旋极化通过三重态-三重态能量转移传递到受体上，塞曼量子数守恒，并用交换机制进行了解释。(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含氮自由基的相互作用。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。用电子和/或自旋交换机制解释了氮氧自由基中观察到的自旋极化ESR信号。(4)三重态苯基的自旋极化反转：在苯溶液中，用苯基-氢原子供体(苯胺、苯酚)体系的光照射观察到生成的自由基的CIDEP信号。CIDEP信号的极性被给体和苯基浓度以及给体反应性的变化所反转。自旋极化的反转可以用苄基分子间的三重态能量转移以及由非平面结构到平面结构的变化来解释。较少

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