UV-VIS spectroscopy study on porphyrin nanostructures formed by electrostatic interaction

Abstract

Porphyrin nanostructure were fabricated by ordinary electrostatic self - assembly and phase transfer electrostatic self–assembly and characterized using ultraviolet-visible spectrophotometry only. For ordinary electrostatic self-assembly, aqueous solution of the negatively-charged porphyrins - meso-tetra(4-phenylsulphonic) porphyrin (TPPS ₄^4-) and meso-tetra(4-carboxyphenyl) porphyrin (TCPP^4-) (TPPS/TCPP) was mixed with aqueous solution of the positively-charged metalloporphyrins - meso-tetra(4-pyridyl) porphyrin [MTPyP (M=Zn, Ni, Co and Mn)]. In the case of phase transfer technique, the aqueous solutions of the negativelycharged porphyrins were (TPPS/TCPP) added to dichloromethane solution of MTPyP. The aqueous and organic phases were studied separately. The electronic spectra of TPPS-MTPyP using ordinary electrostatic self-assembly technique showed the typical J-aggregation influenced by TPPS with bands around 492 nm and 708 nm. These bands were absent in the case of TCPP-MTPyP instead, there was a shift of the absorption bands to shorter wavelength, indicating H-aggregation. For the phase-transfer electrostatic self-assembly technique, the electronic spectra were quite complex and bands were narrower than expected for aggregation. This was indicative of very weak or no aggregation occurring.

Keywords: Porphyrin, Electronic, Spectra, Absorbance, Nanostructures