In　this　study,　the　noncovalent　functionalization　of　graphene　with　cationic　porphyrins　in　an　aqueous　medium　was　investigated　using　UV-vis　and　fluorescence　approaches.　To　characterize　the　interaction　between　graphene　and　cationic　porphyrins,　5,10,15,20-tetra　(4-pyridyl)-21H,23H-porphine,　5,10,15,20-tetrakis　(1-methyl-4-pyridinio)　porphyrin　tetra　(p-toluenesulfonate)　and　5,10,15,20-tetrakis　(4-trimethylammoniophenyl)　porphyrin　tetra　(p-toluenesulfonate)　porphyrin　were　chosen　as　reagents.　The　intermolecular　interactions　were　found　to　occur　immediately　after　mixing　the　cationic　porphyrins　with　graphene.　The　absorption　spectra　of　the　cationic　porphyrins　after　mixing　with　graphene　showed　distinct　red　shifts　of　the　Soret　and　Q-bands　compared　to　free　cationic　porphyrins　indicating　that　interactions　occur　between　the　cationic　porphyrins　and　graphene.　A　strong　fluorescence　quenching　of　the　cationic　porphyrins　in　the　presence　of　graphene　indicated　that　efficient　electron　or　energy　transfer　occurred　from　the　excited　state　of　the　cationic　porphyrins　to　graphene.　Cationic　porphyrins　were　immobilized　on　the　surface　of　graphene　through　electrostatic　and　pi-pi　stacking　interactions,　and　the　chemical　shape　of　graphene　played　an　important　role　in　the　intermolecular　interactions　and　the　red　shift　extent　of　cationic　porphyrins　is　mostly　dependent　on　the　functional　groups　and　charges　of　the　graphene　surface.　The　results　show　that　less　functional　groups　on　the　graphene＇s　surface　and　edge　would　lead　to　stronger　pi-pi　stacking　interactions　between　graphene　and　cationic　porphyrins.　(C)　2011　Elsevier　B.V.　All　rights　reserved.