With the aim to explore the relationship between the structure of conjugated polymers and the performance of their corresponding photodetectors, four donor–acceptor type conjugated polymers were designed and prepared through the convenient Suzuki coupling reaction, in which the structure of the acceptor group, phenazine moieties, changed with different planar π-systems from small to a little bigger, accompanied with a subtly adjusted HOMO and LUMO. The fabricated photodetectors of these four polymers confirmed that the minor structural difference would lead to very different device performance, with the highest photodetectivity, up to 6.2 × 10¹² Jones, and the fastest rise time of 160 μs.