Peripheral modification strategy to create a family of multiply hemiporphycene-fused expanded porphyrins

Novel π-conjugated molecules have consistently been at the forefront of chemical research due to their broad application prospects in fields such as nonlinear optics, biosensing, and electronic memory. In this context, fused porphyrin oligomers have attracted considerable attention as an important platform for realizing characteristic electronic states and associated optical properties. Although post-modification strategies have shown certain unique advantages in creating fused porphyrin oligomers, achieving efficient and precise peripheral modification of porphyrins remains challenging.

A novel concise and efficient synthetic strategy for peripheral modification of porphyrins was developed by a research team at Hunan Normal University. Published in Science China Chemistry, the researchers used peripherally pyrrole-substituted porphyrins as substrates and successfully constructed multiple hemiporphycene–porphyrin fused systems via Friedel–Crafts-type electrophilic substitution and intramolecular Heck cyclization reactions. The structures of these expanded porphyrins were unambiguously confirmed by X-ray single-crystal diffraction analyses. It was observed that as the number of fused hemiporphycene units increased, the degree of molecular distortion gradually intensified.

The photochemical and electrochemical properties of this system were equally striking. The UV–vis absorption spectra exhibited full-range absorption across the visible region, and some fused species showed fluorescence emission up to 850 nm. Owing to the electronic coupling among multiple fused hemiporphycene units, the entire series of compounds displayed rich reversible redox behavior. In particular, triply and quadruply hemiporphycene-fused Ni(II) complexes (denoted as 3Ni and 4Ni, respectively) possessed as many as eleven reversible redox potentials, demonstrating significant potential as multi-electron storage materials.