Functional Bis/Multimacrocyclic Materials Based on Cycloparaphenylene Carbon Nanorings

Abstract

Topologically unique nanocarbon materials with optoelectronic potential are both fascinating and challenging synthetic targets. Their distinctive molecular topologies often lead to chirality, unique optoelectronic properties, and encapsulation capabilities, stimulating advances in synthetic chemistry and materials science. The research on curved nanocarbon materials has garnered substantial interest due to the intricate relationship between their π-conjugation and molecular geometry, as well as their emerging applications in various fields. The introduction of curvature significantly affects the redox behaviors, optical properties, charge-transport capabilities, and self-assembly processes of these nanocarbon materials. The representative examples of curved aromatic systems are cycloparaphenylenes (CPPs) and related carbon nanorings. In these molecules, the nonplanar aromatic structures can induce unique radial π-conjugation and further endow them with distinctive photophysical properties. By adjusting the number of benzene rings in a CPP or incorporating diverse polycyclic aromatic hydrocarbon units, researchers can finely tune the optical and electronic properties of these nanostructures. Many potential applications can be discovered in the fields of fluorescent probes, organic light-emitting diodes (OLEDs), and optoelectronic devices. These properties establish CPP as an important scaffold to create novel carbon nanostructures. With the ongoing advancements in molecular topology, new opportunities are emerging within the fields of materials science, molecular electronics, and biomedicine. Given the exceptional electronic and photophysical properties of CPPs, there has been considerable interest in the development of topologically intriguing bis/multimacrocyclic architectures. It is anticipated that high dimensionality and unexplored topologies will endow these bis/multimacrocycles with unparalleled physical and chemical properties. This concise Account highlights recent developments from our research group on topologically functional materials based on CPP carbon nanorings, particularly their potential applications. Our discussion focuses on (i) the design and synthesis of a series of fully sp²-hybridized all-benzenoid bismacrocycles, as well as [n]cycloparaphenylene-pillar[5]arene bismacrocycles; (ii) the construction of all-CPP-based long π-extended polymeric segments of the armchair SWCNT; and (iii) the synthesis of CPP-based mechanically interlocked molecules, specifically [12]CPP-[3]catenane. Structures like these CPP-based bis/multimacrocyclic architectures exhibit distinct properties─including radial π-conjugation, supramolecular properties, chirality, and unexpected dual-emissive and anti-Kasha photophysical characteristics due to their nonplanar geometries─that allow precise tuning of their HOMO–LUMO gap, emission profiles, and charge-transport behaviors. These properties make them promising for applications in OLEDs, circularly polarized luminescence (CPL) materials, lithium-ion batteries (LIBs), and photoelectroactive devices. By discussing recent work, we demonstrate the potential of these carbon nanorings for future technologies in optoelectronics, chiroptics, and nanotechnology. We also discuss challenges and future directions, emphasizing the importance of precise control over the size, shape, and conjugation of these topological structures to broaden their applications in molecular machines, sensors, and functional materials.