Emerging applications of carbon nanohoops

A cycloparaphenylene can be thought of as the shortest possible cross section of an armchair carbon nanotube. Although envisioned decades ago, these molecules-also referred to as carbon nanohoops-can be highly strained and, thus, eluded chemical synthesis. However, the past decade has seen the development of methods to access carbon nanohoops of varying size and composition. In contrast to many carbon-rich materials, the nanohoops are atom-precise and structurally tunable because they are prepared by stepwise organic synthesis. Accordingly, a variety of unique, size-dependent optoelectronic and host-guest properties have been uncovered. In this Review, we highlight recent research that aims to leverage the unique physical properties of nanohoops in applications and emphasize the connection between structure and properties.