FRET-Relayed Magneto-Photoluminescence Driven by Triplet-Pair Dynamics in Organic Films

Abstract

Spin-correlated excited states in organic semiconductors enable magnetic-field modulation of photoluminescence and provide a sensitive probe of spin-dependent exciton dynamics. In most known systems, such magneto-photoluminescence (MPL) originates from triplet-triplet (TT) states, which confines pronounced magnetic responses to a narrow class of intrinsically TT-active materials. Here, we demonstrate a Förster resonance energy transfer (FRET)-mediated relay mechanism that transfers magnetic-field sensitivity from a TT-active donor to an otherwise non-magento-responsive acceptor, thereby functionally decoupling magnetic responsiveness from the chemical identity of the luminophore . Using DBP-doped rubrene films as a model system, we show that the spin-correlated TT-pair dynamics in rubrene are transferred to the DBP emission via efficient FRET, giving rise to MPL from DBP. By regulating molecular packing through dopant concentration and thermally induced crystallization, we systematically modulate the formation and evolution of TT pairs, which in turn governs the magnitude of the relayed MPL. Spectroscopic analysis indicates that DBP emission reports the donor's magnetic-field-dependent modulation of the singlet population driven by TT-pair dynamics, establishing energy transfer as an effective channel to relay magnetically modulated exited-state population dynamics across molecular boundaries. Our findings define a general mechanism by which magnetic-field sensitivity can be introduced into otherwise spin-silent emitters, providing a conceptual framework for extending TT-driven magneto-optical phenomena beyond intrinsically responsive materials.