Amorphous 2-Bromocarbazole Copolymers with Efficient Room-Temperature Phosphorescent Emission and Applications as Encryption Ink

The development of metal-free organic room temperature phosphorescent (RTP) materials is promising but challenging, because spin orbit coupling is less efficient without heavy metals such as platinum and palladium. Here, we present a novel, amorphous copolymer composed of 2-bromocarbazole phosphor and acrylamide on its side chains, which can engender blue purple phosphorescence emission with high quantum yield at room temperature. The polymer matrices of acrylamide and the hydrogen bonding in the polymeric chain system can effectively help to inhibit nonradiative transition process and, hence, strengthen the phosphorescent emission. The molar ratio of the 2-bromocarbazole phosphor and acrylamide remarkably influences the RTP emission intensities and quantum yields of the polymers. The high amount of phosphor will weaken the rigidity of the polymers and the shielding effect from oxygen., thus leading to a decrease in their RTP emission, while a low concentration of the phosphor will also weaken their RTP emission intensity, Furthermore, RTP intensity of the amorphous polymer is responsive-to humidity, because the hydrogen bonding in the polymeric chain system can be broken by water, which makes it applicable in the area of encryption.