Stable dispersions of exfoliated graphene in aqueous media with the aid of the amphiphilic block copolymer poly(isoprene-b-acrylic acid) (PI-b-PAA), in the form of its anion, were used to electrostatically bind cationic 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphine tetra(p-toluenesulfonate) (H2P4+). A new graphene/PI-b-PAA−–H2P4+ ensemble was formed and examined by dynamic light scattering, UV/Vis and fluorescence emission spectroscopy. The efficient fluorescence quenching of H2P4+ in the graphene/PI-b-PAA−–H2P4+ ensemble was probed by using steady-state and time-resolved photoluminescence, suggesting that electron/energy-transfer phenomena occur within the nanoensemble. Blank experiments validated the concept of electrostatic interactions that govern the formation of graphene/PI-b-PAA−–H2P4+ ensemble, which signified the importance of graphene as an electron acceptor toward the preparation of some new donor–acceptor systems. Finally, kinetic analysis of the lifetime profiles of the fluorescence emission gave information regarding the quenching rate constant and quantum yield of the singlet excited state of H2P4+ in the graphene/PI-b-PAA−–H2P4+ ensemble.