Studies on Energy Transfer with Spin Polarization Conservation in organic Photochemical Reactions

研究了溶液中三重态-三重态能量转移过程中的自旋极化守恒。1984年，我们首次证实了中性吡啶基自由基二聚体的光化学裂解现象，这对解释分子能量转移机理具有重要意义。取得了如下结果：1.吡啶基自由基的单体-二聚体平衡及其光化学。中性吡啶基自由基基本上与它们的二聚体平衡，并且二聚体显示产生自由基的光化学裂解。对初始过程的时间分辨EPR研究揭示了光解的前体是单重激发态。另一方面，在适当的三重态敏化剂的存在下，三重态-三重态能量转移与自旋极化守恒发生导致通过激发三重态的自由基的产生。对许多吡啶基二聚体的详细研究建立了吡啶基自由基的特征化学。分子内三重态-三重态能量转移过程中的自旋极化守恒。这一现象已成功地证明了由瞬态三重态EPR光谱的测量两种类型的螺环化合物含有能量供体和受体部分。自旋排列在分子坐标系中是守恒的，高场近似不能解释光谱的自旋极化模式.其他光化学过程。阐明了下列标题的光化学初始过程：（1）芳香羰基化合物光化学反应产生自由基的CIDEP研究;（2）4-取代吡啶光化学夺氢反应的时间分辨EPR研究;（3）非磷光性环庚三烯酮激发三重态的时间分辨EPR研究。

The studies have been carried out to clarify the spin polarization conservation during triplet-triplet energy transfer in fluid solution. This phenomenon first demonstrated by us in 1984 for the photochemical cleavage of the dimers of neutral pyridinyl radicals is important to interpret molecular energy transfer mechanism. The following results have been obtained.1. Monomer-dimer equilibrium of pyridinyl radicals and its photochemistry. Neutral pyridinyl radicals are substantially in equilibrium with their dimers and the dimers show photochemical cleavage producing the radicals. Time-resolved EPR studies on the initial process disclosed the precursor of photolysis to be the singlet excited state. On the other hand, in the presence of an appropriate triplet sensitizer, triplet-triplet energy transfer with spin polarization conservation occurred leading to the generation of the radical through excited triplet state. Detailed studies on many pyridinyl dimers established a characteristic chemistry of pyridinyl radicals.2. Spin polarization conservation during the intramolecular triplet-triplet energy transfer. This phenomenon was successfully demonstrated by the measurements of transient triplet EPR spectra for two types of spiran compounds containing energy-donor and acceptor moieties. Spin alignment is conserved in the molecular frame and high field approximation can not explain the spin polarization pattern of the specatra.3. Other photochemical processes. The photochemical initial processes have been clarified for the following titles : (1) CIDEP studies on radicals produced from photochemical reactions of some aromatic carbonyl compounds ; (2) Time-resolved EPR studies on photochemical hydrogen abstraction reactions of 4-substituted pyridines ; (3) Time-resolved EPR study on the excited triplet state of non-phosphorescent tropone.