Employing racemization strategies to simultaneously enhance the quantum yield, lifetime, and water stability of room-temperature phosphorescent materials

Abstract

Room temperature phosphorescence (RTP) materials are increasingly recognized for their superior luminescent properties, which are pivotal in applications such as anti-counterfeiting, information storage, and optoelectronics. Despite this, the sensitivity of most RTP systems to humidity presents a significant challenge in achieving durable RTP performance in aqueous environments. This study proposes a strategy to enhance organic room-temperature phosphorescence through racemization. By incorporating external racemates of various chiral phosphors—NDBD-Ph, NDBD-Ph-Ph, NDBD-CH₃, and NDBD-O-CH₃—into a polyacrylonitrile (PAN) matrix, we significantly enhance the RTP properties (quantum yield, lifetime, and afterglow-time) of the resultant films. This enhancement can be attributed to the increased density of racemic molecules in the matrix and the increased spin–orbit coupling (SOC), facilitating the development of a long-lasting polymer RTP system in water. Notably, the racemic rac-NDBD-Ph@PAN film exhibits a persistent bright turquoise afterglow, even after immersion in water for a month. Furthermore, for the first time, we achieved an enhanced green to cyan RTP response to pH variations under both acidic and alkaline conditions (pH = 2–12), with the maximum phosphorescence emission intensity increasing up to threefold. The remarkable water stability, reversible response characteristics, and enhanced phosphorescence properties of this system offer promising potential for dynamic information encryption in aqueous environments.