Self Aggregation of Cationic Porphyrin in Water

Abstract

Abstract Self aggregation of 4,4′,4″,4'″-(21H,23H-porphine-5,10,15,20-tetrayl)tetrakis[1-methylpyridinium] cation (TMPyP4+) in water has been verified by means of fluorescence and 1H NMR spectroscopy. The novel fluorescence behavior of TMPyP such as extraordinarily red-shifted Q(0-0) fluorescence band, blue shift of this band upon dilution, effects of added sodium chloride and sodium dodecyl sulfate micelles, and short fluorescence lifetime strongly suggests the formation of a stacking-type dimer of TMPyP4+ at the TMPyP concentrations above 1×10−6 mol dm−3. The 1H NMR signal due to the porphyrin ring protons was observed as a broad singlet even though the concentration of TMPyP in D2O was 1×10−5 mol dm−3 while the signal in DMSO-d6 was a sharp singlet, suggesting the spontaneous association of TMPyP4+ to form the face-to-face dimer having a considerably loose structure. The π–π interaction has been assumed to be enhanced upon photoexcitation.