We report here the structure-property correlations in a new N-methylfulleropyrrolidine derivative mediated 3-mercaptopropanoic acid capped gold nanocomposite, designed, synthesized and monitored by UV-visible spectroscopy, transmission electron microscopy, dynamic light scattering and pH of the reaction medium. The computational assessments further provided in-depth knowledge on the nanocomposite structure and interaction. In addition, the composite's interaction with a pure fluorescent dye, Rhodamine B, implied energy transfer from the dye to the composite, studied via fluorescence lifetime spectroscopy. A significant quenching in photoluminescence intensity and shortening of the lifetime of the pure dye were revealed upon its interaction with the composite. Upon changing the molar ratio, a characteristic surface energy transfer (SET) from the dye to the composite following a distance dependence of 1/r4 was concluded. This investigation into correlation between spectroscopic properties and nanoscale structure provided a base for novel functional materials. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.