Open-Chain Tetrapyrroles Meet Metal Ions in the Functional Molecular Material Science.

Open-chain tetrapyrroles and their analogues, consisting of four pyrrole rings linked by methylene or methine carbons, originate from natural and synthetic pathways. These compounds exhibit unique structural flexibility due to their extended π-conjugation and tunable coordination with metal ions, enabling precise control over electronic and geometric properties. Such structural versatility makes them promising candidates for chiroptical, optoelectronic, and biorelated applications. By modulating metal coordination and molecular design, their functionalities can be tailored for circularly polarized luminescence, ion sensing, photothermal conversion, and chiral devices. This review highlights recent advancements in open-chain tetrapyrrole-based materials, emphasizing their structure-property relationships and potential for next-generation functional materials.