Heterofission Mechanism for Pure Organic Room Temperature Phosphorescence

Abstract Room temperature phosphorescence (RTP) from pure organic materials, whether in crystalline or film phases, has recently attracted considerable attention. Experimental evidence increasingly suggests that RTP originates from isomeric dopants (impurity) rather than pure compounds. The underlying mechanism and molecular design principles have remained elusive. Herein, the “heterofission mechanism” for RTP is proposed, wherein a singlet excited state is split into two triplets, one remains within the host, while the other migrates to the guest (dopant) molecule, satisfying E_host(S₁) ≈ E_host(T₁) + E_guest(T₁). It is found that all the dopants possess a low triplet excited state, meeting the energy requirement for the heterofission process. The sum of the calculated emission spectra from these two triplets overlaps well with the experimentally measured broad phosphorescent spectra. Furthermore, the calculated heterofission rates are expected to occur at the picosecond timescale. Efficient Dexter energy transfer leads to the guest predominantly dominating the RTP. Based on this mechanism, we can predict potential host and guest candidates to expand the family of pure organic RTP materials.