Deep-Blue Ultralong Room-Temperature Phosphorescence From Halogen-Free Organic Materials Through Cage Effect For Various Applications

Organic room-temperature phosphors with high performances are of great importance for broad range of potential applications. Herein, a new concept of cage effect is proposed to effectively promote room-temperature phosphorescence (RTP) property of organic materials. A novel phosphor, bearing electron-donating carbazole and electron-accepting boronate ester moieties (CBBU) is designed and synthesized. CBBU crystals show multiple photoluminescence including concomitant fluorescence, thermally activated delayed fluorescence (TADF), and RTP. Further doping CBBU in boronate ester crystals (DB/CBBU) boosts remarkably deep-blue RTP emission with CIE coordinates (0.15, 0.09) and a lifetime of 3.69 s, which is longer by four orders of magnitude than that of neat CBBU crystals. To the best of knowledge, it is the longest deep-blue organic RTP materials reported so far. To understand this phenomenon, cage effect in terms of bending, twisting, and crowding degrees, as well as interaction of chromophores with cages has been taken into consideration. The results demonstrate that the strong cage effect alleviates effectively molecular motion of chromophores and then promotes simultaneously their RTP efficiency and lifetime. Similar results have also been found in a series of boronate ester derivatives. Furthermore, applications of the efficient RTP materials for temperature measurements, thermal transition detection, and UV sensing are exploited.