Electron spin–lattice relaxation of the triplet state in disordered solids exhibits dispersion

Global analysis of microwave-induced delayed phosphorescence (MIDP) of photoexcited triplet states at 1.2 K is employed to obtain their spin–lattice relaxation (SLR) rate constants, and other relevant parameters. The phosphorescence decay kinetics of quinoxaline in crystalline durene and n-pentane are predicted accurately, but not in disordered solids nor of tryptophan in aqueous glass. For the latter, the decay fits a bimodal SLR distribution; a subset decays with slow SLR and as predicted, while the remainder displays the expected decay properties of fast SLR. Although not following this bimodal pattern, SLR of quinoxaline in disordered solids also exhibits dispersion.