Continuous Tuning of Organic Phosphorescence by Diluting Triplet Diffusion at the Molecular Level

Organic long-persistent phosphorescent materials are advantageous due to the cost-effectiveness and easy processability. The organic phosphorescence is achieved by the long-lived triplet excitons, and the challenges are recognized regarding the various nonradiative pathways to quench the emission lifetime. Taming long-lived phosphorescence is generally engaged with the charge-transfer or exciton diffusion in molecular stacking to stabilize triplet excitons or form a photoinduced ionized state. Herein, we elucidate that the triplet-diffusion can cause a significant quenching that is not thermally activated by using a system of perfluorinated organic complexes. Hence, we suggest a coevaporation technique to dilute a single phosphorescence-emitting molecule with another optically inactive molecule to suppress the diffusion-induced quenching, tuning the phosphorescence lifetime and spectral features continuously. The work successfully suggests a general semitheoretical method of quantifying the population equilibrium to elucidate the loss mechanisms for organic phosphorescence.