Spectroscopic studies on the interaction of tetramethylpyridylporphyrins and cationic clays

In the present work, the interaction between 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23 H-porphine (TMPyP) and its metallated form (CoTMPyP) with three cationic clays was investigated by X-ray diffraction (XRD), UV-VIS and resonance Raman spectroscopies. Sodium montmorillonites K10 and KSF and a synthetic fluorohectorite (FHT) containing different macrocycle loadings, were prepared by an ion exchange reaction. In nonsaturated KSF and FHT, the CoTMPyP molecule assumes a flat orientation, relative to the host layers, giving rise to at least two absorption bands in the Soret region (ca. 445 and 465 nm) assigned to adsorbed and intercalated CoTMPyP, respectively. For the delaminated K10 sample, a broad band centered around 456 nm, indicates a major contribution from the metalloporphyrin on the clay external surfaces. The electronic spectra of FHT samples containing increasing amounts of CoTMPyP show bands red shifted even when a small amount of porphyrin is used, suggesting that the electronic levels of the macrocycle are more affected by the interaction with the clay than by the metalloporphyrin distortion inside the galleries. The resonance Raman spectra obtained for all CoTMPyP samples presented only minor shifts in peak positions and band width, with the exception of the FHT saturated sample, where the bands are clearly broader when compared to other loadings, suggesting that porphyrin aggregation is occurring. In the case of TMPyP, the bands at ca. 430 and 468 nm were assigned to nonprotonated and protonated molecules, respectively. This assignment is supported by resonance Raman spectroscopy, which also showed the nu(2) mode (ca. 1550 cm(-1)) to be the most sensitive peak to protonation.