High‐Temperature‐Available Organic Blue Phosphorescence for Optical Waveguide

Abstract Organic phosphorescence holds significant potential for its important applications in sensors, optoelectronics, and security technologies. However, achieving long‐lived blue phosphorescence, particularly at high temperatures, remains a significant challenge. In this work, an unusual thermally enhanced blue phosphorescence is investigated and observed in a readily synthesized polymer (P1), which is created by copolymerizing acrylamide with a phenyl terpyridine‐containing monomer (M1). Remarkably, P1 exhibits ultra‐long cyan phosphorescence at 493 nm with a lifetime of 1.04 s at room temperature and an enhanced blue phosphorescence at 450 nm when exposed to a high temperature of 150 °C. Experimental and simulation results suggest that the high‐temperature blue phosphorescence originates from thermally activated rotation of the phenyl terpyridine group, triggering a conformational transition from the low‐energy Iso2 to the high‐energy Iso3 state. Furthermore, this heat‐resistant phosphorescent polymer can be easily fabricated into a high‐temperature optical waveguide with a low optical loss coefficient, making it suitable for high‐performance optical switches. This work provides a novel strategy for designing high‐temperature‐resistant phosphorescent materials, with promising applications in advanced photonic and optoelectronic devices.