Achieving persistent room-temperature phosphorescence from phenanthridone derivatives by molecular engineering

Organic room-temperature phosphorescence (RTP) materials have emerged as promising candidates for various applications. However, persistent organic RTP materials are still rare and are limited to specific chromophore backbones as most organic molecules possess inefficient intersystem crossing. Herein, a facile molecular engineering strategy is proposed to impart tunable persistent RTP properties to phenanthridone (PTD) derivatives through substituent effects. Notably, by adjusting the electronic effect or position of substituents, an ultralong lifetime of 114.90 ms is achieved in the PTD-BnCl crystal. Single-crystal structure analysis shows that the variation in the electronic effect or position of substituents can significantly affect intermolecular interactions and molecular packing, thus giving rise to a remarkable influence on the RTP properties of PTD derivatives in bulk crystals. Furthermore, theoretical calculations not only reveal the mechanism of persistent RTP emission but also elucidate the impact of substituent effects on RTP properties from the molecular and crystalline perspectives, respectively. These simple PTD derivatives with persistent RTP properties are reported for the first time and will help enrich the diversity of organic RTP chromophores. A facile design strategy based on molecular engineering is proposed for the first time to achieve a series of PTD derivatives with tunable persistent RTP properties through substituent effects.