Self-assembly of porphyrin-based supramolecules and their characteristics on gold nanoparticles

A new type of porphyrin-based supramolecules (CoTPPS–MV–MV2+), formed by tetrakis(4-sulfonatophenyl)porphyrin cobalt(II) (CoTPPS), 4,4′-bipyridine (MV) and 4,4′-bipyridinium chloride (MV2+) was designed, assembled and characterized by UV–vis spectra, fluorescence spectra and cyclic voltammetry. The influence of each constituent in porphyrin-based supramolecules on the structure of the supramolecules was discussed. The supramolecules self-assembled on the surface of gold nanoparticles resulted in a red-shift of the absorption bands of gold, declaring the formation of the aggregates between gold and porphyrin-based supramolecule. The fluorescence of porphyrin-based supramolecules was quenched after porphyrin-based supramolecules assembling with gold nanoparticles, implying the energy transformation in the assembled system. TEM images showed the formation of the spherical-like aggregates in the solution of porphyrin-based supramolecules and gold sol. The results of cyclic voltammograms demonstrated the strong binding of the porphyrin-based supramolecules on the surface of the gold nanoparticles.