Using coherent dynamics to quantify spin coupling within triplet-exciton/polaron complexes in organic diodes

Quantifying the spin-spin interactions which influence electronic transitions in organic semiconductors is crucial for understanding their magneto-optoelectronic properties. By combining a theoretical model for three spin interactions in the coherent regime with pulsed electrically detected magnetic resonance experiments on $\ensuremath{\pi}$-conjugated polymer diodes (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]), we quantify the spin coupling within complexes comprising three spin-1/2 particles. We determine that these particles form triplet-exciton/polaron pairs, where the polaron-exciton exchange is over five orders of magnitude weaker ($l170$ MHz) than that within the exciton. This approach provides a direct spectroscopic approach for distinguishing between coupling regimes, and to test hypotheses relating microscopic properties to bulk characteristics of organic electronic devices.