Orange-red and white-emitting nonconventional luminescent polymers containing cyclic acid anhydride and lactam groups

Polymeric luminescent materials containing nonconventional chromophores are of great fundamental and practical importance. However, most nonconventional polymeric luminogens (NPLs) normally emit in the blue region. In this work, we synthesized poly(itaconic anhydride-co-vinyl caprolactam) (PIVC) and poly(itaconic anhydride-co-vinyl pyrrolidone) (PIVP) copolymers through a conventional free radical precipitation copolymerization method. The photoluminescence of the copolymers in solutions and in the solid state is studied. PIVC and PIVP exhibit obvious aggregation enhanced emission (AEE) and aggregation induced emission (AIE) characteristics, showing maximum emission wavelengths in the orange-red region (627 nm and 611 nm), and, very impressively, emit orange-red and bright white emissions under 365 nm UV irradiation, respectively. The copolymers show concentration-dependent luminescence, as their emissions change from blue to orange with the increase of polymer concentration. In addition, they also exhibit significant excitation-dependent fluorescence (EDF) characteristics and emit dark red light when excited with red light. The fluorescence mechanism of the copolymers has been discussed by comparing the PL behaviors of the homopolymers and the structures of the polymers, focusing on possible interactions between cyclic acid anhydride and lactam groups. This study provides a strategy for preparing nonconventional luminescent polymers with strong and red-shifted fluorescence emissions.