π-Conjugated polymers based on flexible heteroatom-containing complexes for precise control of optical functions

Controlling the optical properties of π-conjugated polymers is a relevant strategy to satisfy growing demands for the development of next-generation optoelectronic devices and luminescent materials. Generally, planar and rigid monomers have been used to improve the performance of polymers by enhancing intermolecular electronic interactions and delocalizing π-electrons with polymer main chains. In contrast, we demonstrate that introducing flexible monomeric units with heteroatom-containing complexes into the polymer main chains provides unique functions and the ability to precisely control their optical properties. Due to the slightly bent and asymmetric structures against the π-surface created by boron and O,N,O-type tridentate ligands, large structural relaxation in the excited state occurs with bending motion. This relaxation leads to stimuli-responsive solid-state emission, such as aggregation-induced emission (AIE) and crystallization-induced emission (CIE) properties. Through these structures, π-conjugation and electronic interactions between polymer chains are extended. The resulting π-conjugated polymers show bright emission even in the near-infrared (NIR) region, sensitive stimuli-responsiveness, and high carrier mobility. Our strategy could provide novel insights for improving the functionality of conventional π-conjugated polymers and provide a breakthrough in the development of polymer-based material science.