Development of functional molecular assemblies based on programmable construction of face-to-face assemblies of metallo-porphyrinoids

Metallo-porphyrinoids are known to possess various unique physical and chemical properties depending on their porphyrinoid skeleton structure, as well as the nature of their central metal ions. A useful strategy for the production of novel functional molecular assemblies, utilizing metallo-porphyrinoids as molecular modules, is to assemble them in a cofacial fashion. Such assemblies allow synergistic inter-component electronic communication, or functional cooperativity among the components to achieve unique functions. In this sense, programmable construction of discrete cofacial assemblies composed of different types of metallo-porphyrinoids is appealing because the their functions can be controlled by changing various parameters, namely the relative distance, relative angle, number, and nature of assembled components. However, as porphyrinoids are prone to self-assemble with face-to-face geometry to produce one-dimensional polymeric structures because of their highly planar structure, it is challenging to construct diverse face-to-face assemblies of metallo-porphyrinoids in a pre-designed fashion. In order to overcome these difficulties, appropriate synthetic methodologies are necessary. These are broadly divided into two approaches; one is to utilize covalent bond formation, and the other is to utilize non-covalent interactions. This review summarizes synthetic methodologies applied toward the programmable construction of discrete cofacial assemblies composed of various metallo-porphyrinoids.