Functional Nanoloops: Strain-Promoted Modification of Acetylene-Containing Cycloparaphenylenes

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The project aims to merge the highly topical research fields of cycloparaphenylenes (CPPs) with reactive acetylenes, to afford a library of functionalized CPP-derived nanoloops. The resulting scaffolds will be studied in-depth concerning their qualification as functional materials for application in organic electronics.The synthetic strategy relies on the transformation of a reactive acetylene moiety that is embedded within the CPP framework, into its corresponding ethylene derivative through cycloaddition chemistry with suitable partners. Indeed, preliminary density functional theory (DFT) calculations have shown a significant reduction of the inherent strain energy on going from the acetylene-incorporating CPP to its ethylene congener, which is predicted to provide for significant rate enhancements. The Strain-promoted transformations are grounded on well-established reactions within the realm of acetylene chemistry, such as Diels-Alder, [2+2]-cycloaddition-retroelectrocyclization or cyclotrimerization reactions that will allow the introduction of a broad variety of functional moieties into the macrocyclic CPP backbone. This approach will provide versatile access to tailored nanorings with appealing properties. The resulting compounds will serve e.g. as fluorescent components in organic light-emitting diodes or macrocyclic hosts for encapsulation of fullerene-type guests to foster energy/electron transfer processes.Beyond that, the acetylene-containing CPPs represent valuable molecular building blocks for the formation of covalent 2D networks on metal surfaces and in solutions. The strain-promoted functionalization approach will be applied to fabricate such carbon-rich 2D polymers with high structural precision on defined metal surfaces through thermal activation. The preparation and characterization of these 2D architectures will be carried out by scanning probe microscopy techniques (STM and AFM) supported by DFT calculations to corroborate the experimental results and gain deeper insight into electronic properties and band structures. Needless to say, such porous graphitic nanomaterials – highly topical, yet elusive targets – are not only vital for molecular-scale sensors, membranes and electronics, but also of fundamental scientific interest owing to their unique optoelectronic properties.In summary, the project not only tackles the current bottleneck of synthetic accessibility of functionalized CPP-derived entities, but also opens up an avenue towards versatile macrocyclic building blocks for host/guest studies and atomically defined 2D nanomaterials. As such, the results of the project will provide a fundamental and versatile tool to other researchers from different fields for the design and synthesis of unprecedented materials with tailored optoelectronic and material properties.