A hydrogen bonding strategy to strengthen room temperature phosphorescence of nitrogen-modified benzocarbazole

Abstract

This study designed and synthesized a series of carboxyl-functionalized benzocarbazole derivatives (including BCz-PhCOOH, NBCz-PhCOOH, 2NBCz-1-PhCOOH, and 2NBCz-2-PhCOOH). By uniformly dispersing them into a polyvinyl alcohol PVA matrix, flexible films exhibiting highly efficient and color-tunable room-temperature ultralong phosphorescence RTP were successfully fabricated. The nitrogen-atom modification strategy significantly redshifted the phosphorescence emission wavelengths, while the introduction of carboxyl groups markedly prolonged the phosphorescence lifetime and substantially enhanced the phosphorescence quantum yield. For instance, BCz-PhCOOH@PVA achieved a lifetime of up to 1.34 s with a quantum yield of 21.09%, representing a significant improvement over BCz@PVA which showed 14.86%. Notably, 2NBCz-1-PhCOOH@PVA exhibited an exceptionally high quantum yield of 22.74%, far exceeding 0.98% measured for 2NBCz-1@PVA. Mechanistic investigations revealed that the multiple intermolecular hydrogen bonds between PVA and carboxyl groups effectively suppress non-radiative decay, while repulsive interactions between the aromatic hydrogens of the chromophores and PVA's hydroxyl groups further enhance the stability of triplet excitons. Theoretical calculations confirmed that all target molecules exhibit distinct charge-transfer characteristics and singlet–triplet energy gaps can be altered, facilitating efficient intersystem crossing (ISC). Moreover, leveraging the dynamic phosphorescence properties of these polymer-based RTP materials across both temporal and color dimensions, a novel encryption model was developed that utilizes dual-signal combinations of afterglow color and lifetime to achieve high-level information security. This work provides new insights into the application of organic ultralong phosphorescent materials in anti-counterfeiting and optical information storage.