Room-Temperature Ferromagnetism and Near-Infrared Luminescence Enabled by Interchain-Aggregation Control of Open-Shell Donor–Acceptor Alternating Copolymers

Abstract

Charge transfer in alternating donor–acceptor (D–A) conjugated polymers plays a crucial role in the development of organic electronics and spintronics. However, the contribution of intrachain charge transfer to the optoelectronic properties remains poorly understood due to the interference of interchain aggregation. Here, we report an approach to rational control of the interchain interaction of an open-shell D–A polymer through segregation of strongly interactive backbones, from which polymeric side chains are grafted so that the intrachain interaction between donors and acceptors becomes dominant. The grafted bottlebrush polymers are still open-shell, owing to the presence of unpaired conduction electrons along the π-conjugated backbones, resulting in asymmetric electron spin resonance. Meanwhile, the minimized interchain aggregation leads to near-infrared photoluminescence despite the narrow optical band gap. Surprisingly, the intrachain dominating D–A charge transfer and delocalization, together with the long-range structural ordering of these bottlebrush polymers in solid states, enables ferromagnetism both at and below room temperature. The effects of the chain length and the grafting density of the polymeric side chains on the optical and magnetic properties have been studied in detail.