An XPS analysis of the interaction of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin with exfoliated manganese thiophosphate

Composite thin films of (C72H66N8O12S4)yLi2xMn1-xPS3 have been obtained through a solution approach by interacting the tosylate salt of the cationic water soluble 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (H2T4) and MnPS3 exfoliated in the presence of lithium ions. The thin films have been investigated through x-ray diffraction (XRD), ultraviolet/visible (UV/vis) absorption and mainly x-ray photoemission spectroscopy (XPS). N 1s core-level XPS spectra emphasize the presence of three non-equivalent nitrogen atoms, similarly to the film of the pure H2T4 salt. This result, together with the interlayer spacing determined by the XRD pattern and the evidence from absorption measurements, indicates that the porphyrin is intercalated into MnPS3 layers in a non-protonated form and substantially flattened with respect to the free molecule. The striking likeness between the N 1s core levels in the XPS spectra of the composite material, of the H2T4 salt and of the neutral meso-tetrapyridylporphyrin (H2TPyP) suggests that H2T4 is present between the MnPS3 nanosheets together with its counter-ion (tosylate). This hypothesis is confirmed by the observation of a structure which can be attributed to the sulfur of the counterion in the S 2p core-level XPS spectra of the composite material. An analysis of the Mn 2p and 3p, S and P 2p core-level regions through XPS reveals a strong similarity between the starting MnPS3 and the composite material, suggesting that no charge transfer occurs from the guest (H2T4-tosylate) to the host species (MnPS3).