Conspectus
This Account
describes a body
of research in the design and synthesis
of molecular materials prepared from corannulene. Corannulene (C20H10) is a molecular bowl of carbon that can be
visualized as the hydrogen-terminated cap of buckminsterfullerene.
Due to this structural resemblance, it is often referred to as a buckybowl.
The bowl can invert, accept electrons, and form host–guest
complexes. Due to these characteristics, corannulene presents a useful
building block in materials chemistry.
In macromolecular science,
for example, assembly of amphiphilic
copolymers carrying a hydrophobic corannulene block enables micelle
formation in water. Such micellar nanostructures can host large amounts
of fullerenes (C60 and C70) in their corannulene-rich
core through complementarity of the curved π-surfaces. Covalent
stabilization of the assembled structures then leads to the formation
of robust water-soluble fullerene nanoparticles. Alternatively, use
of corannulene in a polymer backbone allows for the preparation of
electronic and redox-active materials. Finally, a corannulene core
enables polymer chains to respond to solution temperature changes
and form macroscopic fibrillar structures. In this way, the corannulene
motif brings a variety of properties to the polymeric materials.
In the design of non-fullerene electron acceptors, corannulene
is emerging as a promising aromatic scaffold. In this regard, placement
of sulfur atoms along the rim can cause an anodic shift in the molecular
reduction potential. Oxidation of the sulfur atoms can further enhance
this shift. Thus, a variation in the number, placement, and oxidation
state of the sulfur atoms can create electron acceptors of tunable
and high strengths. An advantage of this molecular design is that
material solubility can also be tuned. For example, water-soluble
electron acceptors can be created and are shown to improve the moisture
resistance of perovskite solar cells.
Host–guest complexation
between corannulene and γ-cyclodextrin
under flow conditions of a microfluidic chamber allows for the preparation
of water-soluble nanoparticles. Due to an oligosaccharide-based sugarcoat,
the nanoparticles are biocompatible while the corannulene component
renders them active toward nonlinear absorption and emission properties.
Together, these attributes allow the nanoparticles to be used as two-photon
imaging probes in cancer cells.
Finally, aromatic extension
of the corannulene nucleus is seen
as a potential route to nonplanar nanographenes. Typically, such endeavors
rely upon gas-phase synthesis or metal-catalyzed coupling protocols.
Recently, two new approaches have been established in this regard.
Photochemically induced oxidative cyclization, the Mallory reaction,
is shown to be a general method to access corannulenes with an extended
π-framework. Alternatively, solid-state ball milling can achieve
this goal in a highly efficient manner. These new protocols bring
practicality and sustainability to the rapidly growing area of corannulene-based
nanographenes.
In ...