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 pr
oducts, or to study reaction pathways. We propose a new method to redu
ce 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 photosynth
etic reaction centers, for which we have achieved a 40-fold increase i
n the low temperature (23 K) radical pair lifetime.