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 CH 2 , SiH 2 and GeH 2 moieties or chlorine atoms in the GeCl 2 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.