Conformational features of meso-tetrathienylporphyrins and photosensitising properties of their β-1-acetyl-2-oxopropyl derivatives

• Role of conformation in further reactions of porphyrins.
• Role of electronic effects of substituents in further reactions of porphyrins.
• Photosensitising properties of thienylporphyrins.

The difference in the site of electrophilic nitration of meso-tetra-thien-2-yl- and thien-3-yl-porphyrins is explained based on the difference in extended conjugation between porphyrin core and meso-thienyl rings. The significance of resonance in dictating the site of substitution is also explained based on the behavior of tetrakis(5-bromothien-2-yl)porphyrin toward electrophilic nitration. Three new β-1-acetyl-2-oxopropyl-substituted porphyrins are synthesized by Michael addition of acetylacetone group on pyrrole β-nitroporphyrins. The photosensitizing properties of these porphyrins is investigated using porphyrin–TiO2 composites in the degradation of 4-nitrophenol. The results showed the importance of the effect of the position of sulfur on the thienyl ring and the orientation of meso-thienyl groups with the central macrocyclic ring of porphyrins in deciding its efficiency as photosensitiser.

Figure optionsDownload as PowerPoint slide