Buckybowl-Based Nanocarbons: Synthesis, Properties, and Applications

ConspectusThe introduction of a five-membered ring into hexagon-fused networks typically induces strain that causes positive Gaussian curvature, leading to bowl-shaped polycyclic aromatic hydrocarbons (PAHs), often referred to as buckybowls or π-bowls. The interest in buckybowls is derived from their intriguing properties including, but not limited to, pyramidalized sp² carbon atoms, low-lying lowest unoccupied molecular orbital (LUMO), surface charge stabilization, and bowl-to-bowl inversion. In recent years, investigations into the functionalization of buckybowls, as well as the structural aspects related to properties, have made significant progress. Indeed, the functionalization of buckybowls is a major route to increase structural diversity and fine-tune their properties. In particular, the fusion of aromatic rings to buckybowl rims (π-extension of buckybowls) has established a particularly promising synthetic strategy to access a wide range of buckybowl-based nanostructures with unique topologies and properties. A major obstacle, however, is the limited number of appropriate buckybowls, which could be suggested as potential frameworks for further functionalization. Moreover, buckybowls have been typically synthesized by ring-closing reactions, but many of these procedures suffer from the occurrence of considerable strain and lead to an undesired rearrangement. As a result, the development of buckybowl-based nanocarbons with desirable properties is still in its infancy due to the limited structural diversity, functionalization, and scalability.This Account describes our recent progress in the synthesis of buckybowls and buckybowl-based nanocarbons. In our study, diindeno[4,3,2,1-fghi:4',3',2',1'-opqr]perylene (DIP), pyracyleno[6,5,4,3,2,1-pqrstuv]pentaphene (PP), tetracyclopenta[cd,fg,jk,mn]pyrene (TPP), and corannulene are employed as basic structural units, which exhibit a bowl-shaped geometry and offer an ideal platform for functionalization. General bottom-up approaches have been used to access buckybowl derivatives functionalized with peripheral alkynyl and aryl groups. These substituent groups significantly influence solubility, energy levels, and crystal packing, all of which impact their performance. These buckybowls are ultimately converted into π-extended nanocarbons with wide-ranging structural diversity, including doubly curved, rippled, and chiral nanocarbons. Chiral buckybowl-based nanocarbons, where chirality is introduced from quasi-[8]circulene moieties, have high enantiomerization barriers, enabling the separation of the enantiomers. Notably, the rippled nanocarbon containing 10 aromatic rings directly fused to the TPP core exhibits attractive electronic, magnetic, and mechanical properties, which can be further functionalized through the use of well-established chemistry, opening up many possibilities to access unusual carbon allotropes.The assembly with fullerenes is an important application for buckybowls and buckybowl-based nanocarbons. Depending on the peripheral substituent, the binding constant of buckybowls with fullerenes can be tuned. Moreover, buckybowl-based nanocarbons significantly increase the ability to bind fullerenes, resulting in the formation of highly ordered host-guest systems. These features make the nanocarbons excellent molecules for device applications. As expected, these buckybowl-based nanocarbons can function as organic semiconductors for organic field-effect transistors (OFETs), which have mobilities up to 2.30 cm² V^-1 s^-1. The host-guest complexes exhibit highly efficient ambipolar characteristics with nearly balanced mobilities on the order of 10^-1 cm² V^-1 s^-1. In addition, some buckybowl-based nanocarbons show promising applications in photothermal materials with over 90% photothermal conversion efficiency.