Cyclic metalloporphyrin dimers: Conformational flexibility, applications and future prospects

An illustrative spectrum of cyclic metalloporphyrin dimers has been presented here along with their interesting applications. [Display omitted] •An illustrative spectrum of cyclic metalloporphyrin dimers has been presented.•The kind of spacer holding two porphyrin units is responsible to form a large variety of molecular clefts for guest binding.•Different metals in the cyclic dimer enable specific functions either as reactive sites or as regulation sites.•Binding of guests inside the cavity controls the photophysics and electronic properties of guests for numerous spectacular applications.•Emergence of such systems will explore new research avenues in supramolecular chemistry. Over the past few decades, cyclic metalloporphyrin dimers have been significantly exploited in the fields of molecular motion, switches, recognition, biomimetic chemistry, and nanoreactors. Such cyclic dimeric systems have been enticed particular attention owing to their unique conformational properties. The kind of linker used to hold together the two porphyrin units is responsible to form molecular clefts (with different shapes and sizes) that can bind various guest molecules and control their orientation inside the cavity of the cyclic dimer. Moreover, the presence of different metal ions in the cyclic dimers can tune their properties either as reactive sites or as regulation sites. Therefore depending upon the cavity size, metal ion and the substrate interactions with the host frameworks, various cyclic metalloporphyrin dimers have been developed and successfully utilized for numerous spectacular applications. This review illustrates the recent advancement of such cyclic metalloporphyrin dimers based on their remarkable applications. In addition, this review also highlights various other aspects of the cyclic metalloporphyrin dimers (such as basic conformational features, structural aspects, binding ability towards guests, influence of metals etc) along with their bright future prospects.