Theoretical search of a simple characteristic for long-lived organic room-temperature phosphorescence materials with H aggregation

Abstract

Recently, more and more room temperature phosphorescent (RTP) phenomena have been observed in crystals and organic aggregates, which indicates the dependence of RTP luminescence properties on the molecular packing patterns. At present, an important kind of reported RTP material are those possessing H-aggregation, which is considered to suppress fluorescence and improve the lifetime of excited triplet states. Herein, we tried to find a simple characteristic for H-aggregated RTP materials through exploring the processes of electron transition and energy transfer of the dimers in H-aggregation. An interesting phenomenon aroused our interest, i.e., the overlapping area between H-aggregated dimers exhibits strong correlation with the physical parameters characterizing the RTP performance, such as the number of ISC channels, the spin–orbital coupling (SOC) value, the oscillator strengths of singlet states, the energy transfer rate between the triplet states, and the final RTP lifetime. The scanning of the intermolecular relative position shows that an overlapping area within 40–60% could prolong the phosphorescence lifetime, which could be further proved by other H-aggregated crystals. This exploration not only highlights the important role of the overlapping area in characterizing the phosphorescence lifetime, but also provides guidance for developing persistent pure organic RTP materials.