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

研究了流体溶液中三重态-三重态能量转移过程中的自旋极化守恒。这一现象首先由我们在1984年证实，中性吡啶自由基二聚体的光化学裂解对于解释分子能量传递机制具有重要意义。取得了以下成果：1.吡啶自由基的单体-二聚体平衡及其光化学。中性吡啶自由基与它们的二聚体基本上是平衡的，二聚体表现出光化学裂解产生的自由基。对初始过程的时间分辨EPR研究揭示了光解的前驱是单重态激发态。另一方面，在合适的三重态敏化剂存在下，自旋极化守恒的三重态-三重态能量转移导致通过激发三重态产生自由基。对许多吡啶二聚体的详细研究建立了吡啶自由基的特征化学。分子内三重态-三重态能量转移过程中的自旋极化守恒。这一现象已被两类含能量给体和受体结构的螺环化合物的瞬时三重态EPR谱的测量所成功地证明。自旋排列在分子框架中是守恒的，高场近似不能解释光谱的自旋极化模式。其他光化学过程。光化学的初始过程已被阐明如下：(1)某些芳香族羰基化合物光化学反应产生的自由基的CIDEP研究；(2)4-取代吡啶类化合物光化学氢提取反应的时间分辨EPR研究；(3)非磷光酮类化合物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.