Catalytic Control of Diels-Alder Reaction via Photoinduced Electron Transfer

涉及光激发态的光化学反应以及基态的热反应也可以被催化。然而，激发态的寿命通常很短，因此激发态的任何反应都应该足够快，以赶上激发态向基态的衰变。因此，催化剂进一步加速已经很快的激发态反应的可能性似乎很小。一旦电子给体和电子受体对（其中一个为激发态）固定，光诱导电子转移的反应性自动确定。激发态可能与底物有一个能量有利的电子转移途径，否则反应将没有机会与快速的物理衰变竞争到基态（通常寿命为10^<-6> s至10^<-12> s）。尽管存在这些明显的困难，但我们已经开发了一些光化学反应的例子，包括Diels-Alder反应，这些反应涉及催化电子转移过程作为速率决定步骤。建立了光诱导电子转移反应催化的基本概念和光化学氧化还原反应。否则，不太可能发生的是可能有效地进行应用催化光诱导的电子转移步骤。

Photochemical reactions involving photo-excited states can also be catalyzed as well as the thermal reactions of ground states. However, the lifetimes of excited sates are usually very short and accordingly any reaction of the excited state should be fast enough to compete the decay of the excited state to the ground state. Thus, there seems to be little chance of a catalyst to accelerate further the reactions of excited states, which are already fast. The reactivity of photoinduced electron transfer is automatically determined F once the pair of electron donor and acceptor, one of which is an excited state, is fixed. The excited state may have an energetically favorable electron transfer pathway with a substrate, otherwise the reaction would have no chance to compete with fast physical decay to the ground state (typically the lifetime is 10^<-6> to 10^<-12> s). Despite these apparent difficulties, we have developed a number of examples of photochemical reactions including Diels-Alder reactions that involve catalyzed electron transfer processes as the rate-determining steps. Fundamental concepts for catalysis of photoinduced electron transfer reactions have been established and photochemical redox reactions which would. otherwise be unlikely to occur are made possible to proceed efficiently by applying the catalysis on the photoinduced electron transfer steps.