Quantum beats in the recombination fluorescence of radical ion pairs caused by the hyperfine coupling in radical anions

The ratios of the radiofluorescence decay curves for n-decane solutions of 1,2,3,4-tetraphenylcyclopenta-1,3-diene and its silicon and germanium analogs (siloles and germoles) in high and zero magnetic fields have an oscillating component caused by singlet–triplet evolution of the pair S+/A−, where S+ is the solvent hole and A− is the radical anion of the acceptor (a compound added). It is shown that the beats are due to the hyperfine couplings (hfc) with either the protons of CH2, SiH2 and GeH2 moieties or chlorine atoms in the GeCl2 and GeClMe moieties of radical anions. The hfc constants in the anions and spin relaxation times of radical ion pairs were obtained by fitting the experimental curves.