Control of radical pair lifetime by a switched magnetic field

Radicals produced by illumination or ionizing radiation are important in life sciences and chemistry. Reducing the rate of radical decay by recombination can be vital for maximizing the yield of radical pair products, or to study reaction pathways. We propose a new method to reduce the probability for singlet-born radical pair recombination, based on the population of energetically isolated radical pair spin levels, and present an application to photoinduced radical pairs in photosynthetic reaction centers, for which we have achieved a 40-fold increase in the low temperature (23 K) radical pair lifetime.