Multifunctional Nanoparticles of Porphyrins and Phthalocyanines: Review of Synthetic Strategies and Emerging Applications

There is considerable research interest in the synthesis and characterization of organic-based nanoparticles because of the wide range of nanomaterials that can be designed with useful functional properties. With emerging research in the synthesis of organic nanoparticles comprised of porphyrins and phthalocyanines, there is a challenge to prepare multifunctional nanoparticles with the desired properties, size, and composition that are stable in environments that are exposed to stresses of pH, oxidation, or heat. This review describes innovative strategies that have been reported for synthesizing nanoparticles of porphyrins and phthalocyanines for applications. The tunability of the structure of porphyrinoid molecules through synthetic chemistry provides an opportunity to design a diverse range of multifunctional nanoparticles with desired properties, e.g., optical, magnetic, electronic, chemical. Porphyrins and pthalocyanines are macrocyclic compounds which have a rigid aromatic structure, are thermally stable, and have useful photophysical, optical, and electronic properties. Various elements can be inserted within the center of the macrocycles of porphyrinoids, which are held in place by the four nitrogen atoms within the rings. The inserted elements can impart tunable properties to molecular assemblies. Approaches for preparing nanoparticles of porphyrins and composite nanoparticles have been reported that are based on strategies with covalent and/or noncovalent binding chemistries. Methods reported for synthesizing porphyrinoid nanoparticles encompass protocols with solution self-assembly, ultrasonication, mixed solvents, core–shell strategies, laser ablation, host–guest solvents, reprecipitation, and microwave heating. Encapsulating nanoparticles with porphyrins in a core–shell design can impart useful functionalities that are a combination of properties from the inner core material and the chemistry of the outer coating. Nanoparticles of porphyrins and porphyrin-related compounds have been developed commercially for technology in areas such as in biomedicine, photodynamic therapy, catalysis, electronics, and sensors.