© 2021 Elsevier B.V.Manganese phthalocyanine (MnPc) bearing peripherally substituted octacarbazole moieties was synthesized and characterized by matrix-assisted laser desorption/ionization spectrometry (MALDI), FT-IR, and UV–Vis spectroscopy. The complex was then conjugated to graphene quantum dots (GQDs) via π-π stacking and characterized by energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), energy dispersive spectroscopy, and X-ray diffraction. Electrochemical performances of MnPc and its nanoconjugate were investigated using cyclic voltammetry (CV), square wave voltammetry (SWV) and spectroelectrochemistry (SEC) to determine the influence of the carbazole substituents and graphene quantum dots on the redox mechanism of MnPc. Although the carbazole substituents did not significantly influence the reduction processes of MnPc, they induced MnPc coating onto the electrode surface due to cationic electropolymerization of the carbazole substituents. The composite comprising graphene quantum dots and MnPc exhibited redox responses that were comparable to those of MnPc.