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Aggregation-Induced Enhancement of Molecular Phosphorescence Lifetime: A First-Principle Study

Pure organic phosphorescent molecules are promising compounds for applications of phosphorescence, yet their utilization is restricted because of inefficient intersystem crossing (ISC) between singlet and triplet states. Molecular aggregation has been deemed a viable strategy to modulate molecular luminescence in solution, yet its impact on the phosphorescence is rarely investigated. In this work, we carried out first-principle studies to elucidate how aggregation of selected phosphorescent molecules will affect their phosphorescence behavior. Our calculations show that the overall ISC rate is appreciably enhanced, thanks to a decrease of energy gaps (ΔE) and an increase in the number of ISC channels between singlet and triplet states as the degree of aggregation develops. This facilitates singlet-to-triplet conversion. More importantly, the phosphorescence lifetime increases with the increase of the degree of molecular aggregation. The long-lived phosphorescence associated with aggregation benefits from ...