Achieving Efficient Blue Room-Temperature Phosphorescence in Cyclized Aromatic Amides via Hybridized Local and Charge-Transfer State

Abstract

The development of organic blue room-temperature phosphorescence (RTP) materials is challenging, primarily due to the difficulty in simultaneously generating and stabilizing high-energy triplet states. While most reported RTP systems emit in the green or yellow regions, blue-emitting scaffolds remain scarce. Here, we report a series of cyclized aromatic amides (CAAs) that exhibit highly efficient blue RTP in polyvinyl alcohol (PVA) matrices. The optimized CAA demonstrates a phosphorescence lifetime of 2016.9 ms and a quantum yield of 15.6%, representing a 68-fold increase in lifetime and a doubling of efficiency compared to its non-cyclized counterpart. Single-crystal and theoretical analyses reveal that the triplet state of CAAs possesses a hybrid local and charge-transfer (HLCT) character, which is distinct from the predominantly charge-transfer (CT) nature of the non-cyclized analog. The HLCT state maintains a high-energy triplet excited state (T₁) suitable for blue emission, while minimizing spin-orbit coupling (SOC) between T₁ and the ground state (S₀), thereby enabling an ultralong lifetime. Furthermore, the planar rigid scaffold of CAAs, combined with the restrictive PVA matrix, effectively suppresses non-radiative decay, enhancing the overall RTP efficiency. This work establishes CAAs as a promising class of blue phosphors that concurrently achieve high efficiency and an ultralong lifetime, offering a viable design strategy for advanced photonic applications.