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

Abstract

Composite thin films of (C72H66N8O12S4)yLi2xMn1−xPS3 have been obtained through a solution approach by interacting the tosylate salt of the cationic water soluble5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin(H2T4)and MnPS3 exfoliated in the presence of lithium ions. The thin films have been investigated throughx-ray diffraction (XRD), ultraviolet/visible (UV/vis) absorption and mainly x-rayphotoemission spectroscopy (XPS). N 1s core-level XPS spectra emphasize thepresence of three non-equivalent nitrogen atoms, similarly to the film of the pureH2T4 salt. This result, together with the interlayer spacing determined by the XRD pattern and theevidence from absorption measurements, indicates that the porphyrin is intercalated intoMnPS3 layers in a non-protonated form and substantially flattened with respect to the free molecule. Thestriking likeness between the N 1s core levels in the XPS spectra of the composite material, of theH2T4 salt and of the neutral meso-tetrapyridylporphyrin(H2TPyP) suggests thatH2T4 is presentbetween the MnPS3 nanosheets together with its counter-ion (tosylate). This hypothesis is confirmed by theobservation of a structure which can be attributed to the sulfur of the counterion in the S2p core-level XPS spectra of the composite material. An analysis of the Mn 2p and 3p, Sand P 2p core-level regions through XPS reveals a strong similarity between the startingMnPS3 and the composite material, suggesting that no charge transfer occurs from the guest(H2T4-tosylate) tothe host species (MnPS3).