Luminous Butterflies: Rational Molecular Design to Optimize Crystal Packing for Dramatically Enhanced Room‐Temperature Phosphorescence

Abstract In general, the properties of organic molecules for persistent room‐temperature phosphorescence (p‐RTP) rely heavily on the molecular packing in aggregated state, and the molecular packing is highly related to the structure and electronic properties of molecules. Thus, through rational design of molecules, it is possible to control the packing and hence the properties of p‐RTP molecules. In this work, traditional CO is replaced by phthalide (PT) unit to achieve desired molecular packing with strong intermolecular interactions. Butterfly‐like molecules are successfully synthesized, which show bright mechanoluminescence (ML) as well as robust p‐RTP effect with phosphorescence lifetime (τ p ) up to 810 ms and efficiency ( Φ P ) of 5.1%. Compared to their contrastive carbonyl‐only molecules, two butterfly‐like molecules increase their τ p from 12.1 to 810 ms and 1.3 to 396 ms, respectively. Herein, from elaborate molecular structure design to the expected packing, and then to excellent performance, new pure organic p‐RTP and ML molecules are shared for the better understanding of the molecular structure–packing–performance relationship.