Reversible color switching of bright phosphorescence in purely organic materials for advanced data encryption

Purely organic phosphors have emerged as promising materials for various optical applications. Herein, we report a single-component organic phosphorescent crystal, 1,1′-(2,5-dibromoterephthaloyl)bis(glutarimide) (BrGlu), which exhibits fully reversible, pseudopolymorph-dependent phosphorescence color switching. Under standard crystallization conditions, BrGlu forms green-emitting crystal (G-crystal), while crystallization in the presence of CHCl3 yields blue-emitting solvent-inclusion crystal (B-crystal). Notably, G-crystal converts into B-crystal upon exposure to CHCl3, whereas the blue crystals revert to green upon heating, demonstrating a reversible phosphorescence-to-phosphorescence switching mechanism. Through a combination of experimental analyses and quantum chemical calculations, we elucidate the underlying mechanism governing this triplet emission color transformation: syn–anti conformational reorientation of bromine–carbonyl substituents: upon solvent inclusion, hydrogen bonding stabilizes the syn-rotamer to yield bright-blue phosphorescence, whereas gentle heating reverts the system to the anti-rotamer for green emission. Exploiting this property, we develop an advanced data encryption platform featuring a dual-layer security system—phosphorescence emission combined with thermal- or solvent-induced stimuli-response—significantly enhancing security in secure data encryption and anti-counterfeiting. Purely organic room temperature phosphorescent materials are of interest for a range of applications, but phosphorescence colour switching is hard to achieve. Here, the authors report the use of a single-component organic crystal with reversible phosphorescence colour switching.