Spectroscopic studies of nanostructures of negatively charged free base porphyrin and positively charged tin porphyrins

Spectroscopic studies were carried out on the homoaggregates of negatively charged free base meso-tetraphenylsulfonated porphyrin ([H2TPPS4]4−) and heteroaggregates of a mixture of protonated ([H4TPPS4]2−) and tin meso-tetra (N-methyl-4-pyridyl) porphyrin ([SnTMPyP]4+). The spectroscopic studies were done to determine the optimal conditions required for the fabrication of porphyrin nanorods by ionic self assembly of two oppositely charged porphyrins. In addition, the various spectral changes of [H4TPPS4]2− with concurrent change in pH and concentration are also investigated. In acid media at pH <3, and at concentrations >1 × 10−5 M, [H4TPPS4]2− molecules form J aggregates. A mixture of [H4TPPS4]2− and [SnTMPyP]4+ forms heteroaggregates of the J type in acid media. At pH’s 2 to 3, the optimum ratio for the formation of J aggregates is 3:1 and for pH 1, the optimum ratio is 2:1. Transmission electron microscope images of the nanostructures formed show that they are of cylindrical shape.

Graphical abstractA mixture of negatively charged free base protonated meso-tetraphenylsulfonated porphyrin ([H4TPPS4]2−) and tin meso-tetra (N-methyl-4-pyridyl) porphyrin ([SnTMPyP]4+) forms heteroaggregates of the J type in acid media whose Raman microscopic image shows leaf-like structure.Figure optionsDownload full-size imageDownload as PowerPoint slide