Quenching and enhancing behaviour of 1-(4-methoxyphenyl)-2-(4-methylnaphthalen-1-yl)-1H-phenanthro[9,10-d] imidazole (Ligand - MMPI) with Cu –doped ZnO nanoparticle has been studied. Ligand has been characterized by 1H, 13C NMR and mass spectral analysis. Cu –doped ZnO nanoparticle have been synthesised by sol-gel method and characterized by powder X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectra (EDS). Quenching and enhancing behaviour were confirmed by the ligand strongly binding on the surface of Cu –doped ZnO nanoparticle. Increasing concentration of nanoparticles into ligand results in enhances absorbance and quenching fluorescence was observed. Fluorescence quenching was confirmed electron transfer from excited state of ligand to nanoparticle. Theoretical calculations were performed by Gaussian -03 package.