The isosteric replacement of C-C with B-N units is emerging as a powerful method to tune the optoelectronic properties of organic π-conjugated materials. In this work, copolymers based on ladder-type B-N Lewis pair-fused dipyridylfluorene monomers and a thienylated benzothiadiazole (BTDDT) are prepared by Stille-type polycondensation. The polymers containing exocyclic ethyl or pentafluorophenyl substituents on boron are characterized by multinuclear NMR spectroscopy and gel permeation chromatography, which provides estimates of the average degrees of polymerization (DP_n) of 30 (R = Et) and 10 (R = C₆F₅). Electrochemical analyses on thin films reveal two distinct reversible reductions that are assigned to benzothiadiazole- and boron-fused dipyridylfluorene-centered processes. UV‒vis analyses show that the band gaps are significantly lowered relative to both BTDDT and the boron-containing monomers. As a result, the absorption and emission bands are shifted to much lower energies, leading to intense orange emission with maxima at 641 nm (R = Et) and 627 nm (R = C₆F₅), respectively, with quantum yields of over 50%. Computational studies on molecular model dyads offer insights into the effects of the isosteric replacement of C-C units in ladder-type fused bisfluorene with B-N Lewis pairs on the electronic structures of the polymers.