Roth Heinz D
Department of Chemistry and Chemical Biology, Rutgers University, Wright-Rieman Laboratories, New Brunswick, NJ 08854-8087, USA.
Photochem Photobiol Sci. 2008 May;7(5):540-6. doi: 10.1039/b800524a. Epub 2008 Mar 3.
Radical ion pairs generated by photoinduced electron transfer may undergo return electron transfer (RET) in pairs of singlet or triplet multiplicity. RET efficiencies are determined by the free energy of RET and the topologies of the potential surfaces of parent molecule, radical ion and triplet state. If radical ion geometries are different from the corresponding triplet states, RET occurs either with cleavage ("dissociative" RET; 1,2-diphenylcyclopropane radical cations) or formation of C-C bonds ("associative" RET; norbornadiene radical cation). Radical ions of some strained ring compounds spontaneously undergo ring-opening; RET to such species form ring-opened triplets without major geometry changes. CIDNP spectroscopy offers unique insights into triplet RET.
光诱导电子转移产生的自由基离子对可能会以单重态或三重态的形式进行回电子转移（RET）。RET效率由RET的自由能以及母体分子、自由基离子和三重态的势能面拓扑结构决定。如果自由基离子的几何结构与相应的三重态不同，RET会伴随着裂解（“解离性”RET；1,2 - 二苯基环丙烷自由基阳离子）或C - C键的形成（“缔合性”RET；降冰片二烯自由基阳离子）发生。一些张力环化合物的自由基离子会自发地发生开环反应；向这类物种的RET会形成开环的三重态，且几何结构变化不大。CIDNP光谱为三重态RET提供了独特的见解。
