Light-emitting polymers are the core materials for constructing optoelectronic devices, and efforts have been made to further enhance their functionality. In particular, stimuli-responsive luminescent materials are highly useful because they can be used as sensors. Therefore, much effort have been devoted to developing new functional polymers. We have previously discovered that azobenzene-containing polymers can work as versatile luminescent materials. In this paper, to enhance thermal stability of the azobenzene polymers, we designed a new monomer to form the cyclic structure, benzoxazole, based on the azomethine structure. We synthesized two types of conjugated polymers having different types of comonomer units and investigated their optical properties as well as thermal stability. Initially, as we expected, it was found that the synthesized polymers have shown higher thermal stability than those of the corresponding azobenzene polymers. Moreover, the polymers show intense emission both in solution and film. Finally, upon heating, new emission bands originating from new excited species were discovered. Our strategy could be valid for expanding the applicability of stimuli-responsive materials in environmental changes.