Dipole-quadrupole coupling in triplet exciton-polaron quenching in a phosphorescent OLED emission layer

From quantum chemical calculations, triplet-polaron quenching in phosphorescent Ir(ppy)${}₂$acac:m-MTDATA host--guest films, such as those used in OLEDs, is shown to be governed not only by dipole--dipole F\"orster transfer, as is often assumed, but also by quadrupolar interactions. At typical emitter-host separations, quadrupolar contributions even dominate. This work quantifies these contributions by generalizing F\"orster spectral overlap method to dipole-quadrupole coupling, based on near-field quadrupolar absorption. The study resolves a discrepancy between F\"orster radii found from spectral overlap calculations and device experiments.