Comparative studies of magnetic field effect on radical pairs photogenerated by electron transfer from biphenyl to derivatives of phenyl pyrilium salt and to corresponding thio salts

Abstract

We have generated radical pairs (RPs) in SDS micellar medium by electron transfer from the ground state of biphenyl (BP) to various alkyl-substituted phenyl pyrilium cations (PP⁺) and corresponding thio-phenyl pyrilium cations (SPP⁺) and have compared the dynamics of RP recombination in magnetic fields varying from 0 to 5 T. A comparison of PP^·/BP^·+ decay curves with SPP^·/BP^·+ decay curves leads to the conclusion that both ¹RPs and ³RPs are produced in the former case, the temporal behavior at early times being dominated by field-insensitive 1RP and at later times by highly field-sensitive ³RPs. In the case of the SPP^·/BP^·+ system, on the other hand, ³RPs dominate the decay throughout but the field sensitivity is reduced. The large MFE in O-analogues is presumably caused by reduction of micellar escape rate while the reduced MFE for the S-analogues has been ascribed to spin-orbit coupling (SOC).