D–A Clustering-Induced Red Fluorescent Emission of Nonconjugated Maleimide-Based Copolymers

To develop long-wavelength emissive nontraditional luminescent polymers, which is still challenging, electron-withdrawing maleimide (MI) derivatives were copolymerized with a second monomer containing an electron-donating group by using free radical polymerization. Different from nonemissive homopolymers of both MI derivatives and the second monomers, copolymers showed significant long-wavelength emissions. Especially, P(DMAA-co-PMI) (DMAA: N,N-dimethylacrylamide, PMI: N-phenylmaleimide) and P(NIPAM-co-MI) (NIPAM: N-Isopropylacrylamide) exhibited orange-red emissions (595 and 630 nm) in both solution and solid states with an obvious excitation-dependent fluorescence (EDF). The red-shifted emissions of MI-based copolymers were reasonably attributed to the formation of through-space conjugated D–A clusters, which were proved by the existence of van der Waals forces between carbonyl groups and hydrogen bonds of the acceptor and donor groups, as revealed by theoretical calculation computation results.