Diaminopyridine (DAP) ligand is successfully intercalated in GO layers to achieve a layered-type structure with interlayer separation ∼1.03 nm. Density functional theory (DFT) was applied to investigate the stability of the modified structure along with its interlayer separation, and agrees well with the experimental results. As-synthesized diaminopyridine functionalized GO (DAP–fGO) composites show better photoluminescent (PL) property compared with GO via surface passivation. Experimental observation of excitation-dependent PL spectra of DAP–fGO composite was further verified by DFT calculations of HOMO–LUMO band gaps. We believe that this study will help to design different GO-based nanomaterials with potential physical, chemical and optical applications.