<p>π-Conjugated polymers have attracted significant attention due to their tunable optoelectronic properties and potential applications in organic electronics. In this study, we report the synthesis and characterization of novel π-conjugated polyphenylenes (PPs) with poly(<i>o</i>-phenylenediamine) (POPD) graft chains. The graft copolymers were synthesized via oxidative polymerization of <i>o</i>-phenylenediamine (OPD) in the presence of PPs containing 2,3-diamino-1,4-phenylene units. Structural characterization by IR and ¹H NMR spectroscopy confirmed the successful incorporation of POPD side chains onto the PP backbone. The optical properties of the graft copolymers were studied by UV–Vis and photoluminescence spectroscopy, revealing features consistent with an extended π-conjugated system. Electrochemical properties were evaluated via cyclic voltammetry, revealing enhanced redox activity due to the extended π-conjugated system. The incorporation of POPD chains led to increased oxidation and reduction potentials, highlighting their potential for electroactive applications.</p> Graphic abstract <p>Novel π-conjugated polyphenylenes (PPs) with poly(<i>o</i>-phenylenediamine) (POPD) graft chains were synthesized via the oxidative polymerization of <i>o</i>-phenylenediamine in the presence of PPs containing 2,3-diamino-1,4-phenylene units. The graft copolymerization enhanced the photoluminescence and electrical conductivity of the PPs. The materials underwent electrochemical oxidation of the polymer backbone and electrochemical reduction of the graft chains.</p> <p></p>