CONTROL OF SINGLET-PRECURSOR RADICAL PAIR LIFETIME BY MANIPULATION OFSPIN-SELECTIVE REACTION PATHWAYS

Radicals produced by illumination or ionizing radiation are often prod uced in pairs, which quickly decay by recombination or by diffusion an d subsequent reaction. For studying reaction pathways and optimizing t he yield of radical pair products it is desirable to minimize the prob ability of charge recombination. We present here a method based on sim ple radical pair theory to effectively prolong the Lifetime of radical pairs that are formed from an excited singlet state by manipulating t he population of energetically isolated radical pair tripler levels. T wo experimental schemes are discussed and demonstrated on the secondar y radical pair of photosynthetic reaction centers. For this system we have achieved an increase in radical pair lifetime of 1-2 orders of ma gnitude at low temperatures (7 K).