Elastic organic crystals with ultralong phosphorescence for flexible anti-counterfeiting

Ultralong organic phosphorescence (UOP) crystals have attracted increased attention due to the distinct photophysical property of a long-lived lifetime. However, organic crystals are generally brittle, leading to a serious problem for their application in flexible technology. Herein, we report three types of elastic organic crystals (EOCs) with ultralong phosphorescence via introducing halogen atoms (Cl, Br, I) into π-conjugated phosphorescent molecules. Especially, the crystal containing iodine atoms displayed both excellent elasticity (ε = 3.01%) and high phosphorescent efficiency (Φ_Ph = 19.1%) owing to the strong halogen bonds. Taking advantage of its highly efficient UOP and excellent elasticity, we successfully used a DCz4I crystal for anti-counterfeiting application. These findings may provide guidance for the development of elastic crystals with afterglow and expand the scope of potential applications on flexible materials.