Organic Room Temperature Phosphorescence from BN-Substituted Xanthene Derivatives

Emissive organic materials are predominantly fluorescent and there is significant interest in realizing and understanding examples that defy this paradigm and exhibit phosphorescence under ambient conditions. Organic room temperature phosphorescence (ORTP) offers the long-lived excited states and bathochromically-shifted emission maxima of phosphorescence without the use of potentially toxic and expensive transition metals. Most ORTP materials rely on well-studied structural motifs that include aryl carbonyls, sulfones, and heavy main group elements. We report the unexpected ORTP of a series of heavy atom-free BN-substituted xanthene derivatives. The creation of heteroatom-rich scaffolds, combined with stabilizing C-H⋅⋅⋅F interactions in the solid-state, resulted in oxygen-tolerant heavy atom-free organic phosphorescence without relying on the use of cryogenic temperatures, polymer matrices, or host-guest interactions. The observation of ORTP in these simple systems sets a blueprint for the further development of heavy atom-free organic phosphors.