Functional Nanoloops: Strain-Promoted Modification of Acetylene-Containing Cycloparaphenylenes
Solid State and Surface Chemistry, Material Synthesis
Physical Chemistry of Solids and Surfaces, Material Characterisation
Final Report Abstract
The initial goals of this research project were met in that a reliable synthetic route to alkyne-containing macrocycles could be developed and – with the smallest derivative comprising seven phenylenes and one alkyne unit – the limitations of stability could be established. The proposed surface supported formation of 2D covalent networks via [2+2+2]cyclotrimerizations could not be achieved due to the thermal instability of the alkyne-containing macrocyclic precursor, which did not allow for sublimation of this compound onto surfaces. On the other hand, proof of concept for the hypothesized strain-promoted reactivity of alkyne-containing macrocycles was provided by means of a series of transformations from the realm of click-chemistry ([2+2+2]cyclotrimerization, [3+2]cycloaddition, [2+2]cycloaddition-retrocyclization, and [4+2]cycloaddition/elimination). The modular strategy not only bears the potential to access a plethora of other hoop-type compounds and various derivatives but also enables exact control over the reactivity of the incorporated angle-strained alkyne by varying the macrocycle size. Further tuning of sterics, electronics, and the composition of the macrocycle is expected to provide an entirely new class of strained ‘clickable‘ structures based on inherently bent, radially oriented π-rich macrocycles. The findings from this research resulted in several follow-up projects which are currently being pursued. At the focus of these consecutive projects, we envisaged the straightforward functionalization of strained alkynecontaining macrocycles to unlock opportunities in the field of materials science and biomolecular imaging techniques. Hence, these easy-to-conjugate macrocycles – a class of compounds we dubbed ‘nanolassos’ – represent versatile platforms for the click-functionalization of azide tagged surfaces. We found that the shapepersistent macrocyclic addends resulting from strain-promoted [3+2]azide alkyne cycloadditions accommodate fullerenes with high association constants >105 M–1. More importantly, transient absorption experiments could demonstrate excited state energy/charge transfer in suitably decorated supramolecular donor-acceptor dyads which is pointing at potential applications in organic electronics as well as at metal-organic interfaces. In a second project, a series of unprecedented lemniscal bismacrocycles was developed and successfully tested as high affinity materials for detection of small molecular analytes with far-reaching societal and safety implications including restricted, explosive, and toxic substances. We combined extensive experimental methods including X-ray diffraction, gas sorption, and quartz crystal microbalance measurements supported by theoretical DFT calculations to gain a deeper understanding of the underlying host/analyte interactions and solid-state characteristics. Our studies could establish a novel design principle to break up the herringbone packing of molecular hoop-shaped structures – the conceptually simplest intrinsically porous architectures – which may serve as a guideline for the future design of functional solid-state materials.
Publications
- Angew. Chem. Int. Ed. 2018, 50, 16348
T. A. Schaub, J. T. Margraf, L. Zakharov, K. Reuter, R. Jasti
(See online at https://doi.org/10.1002/anie.201808611)
