Frequency response and origin of the spin-1∕2photoluminescence-detected magnetic resonance in aπ-conjugated polymer

Abstract

We model the frequency responses of the photoinduced absorption (PA) and the spin-$1∕2$ photoluminescence-detected magnetic resonance (PLDMR) in the archetypal $\pi$-conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]. We show that the frequency response of the resonance is consistent with a quenching model mediated by spin-dependent interactions between triplet excitons and polarons. Two polaron populations are identified: short-lived paired polarons that may recombine after spin-dependent collisions with triplet excitons, and long-lived unpaired polarons that are unaffected by microwave resonance. The large density of unpaired polarons dominates the frequency response of PA measurements, but does not influence the frequency response of the PLDMR, which instead probes the dynamics of triplet excitons and paired polarons.