Cyclodextrin-Based Supramolecules As Potential Molecular Devices

Abstract

The work presented in this Thesis focuses on the synthesis of cyclodextrin-based supramolecules and the investigation of their potential as molecular devices.

Daisy chains were initially targeted as a promising platform to build extended molecular muscles. Chapter 2 presents the synthesis of an oligomeric series of interlocked, cyclodextrin-based [c2]daisy chains through an innovative approach based on the direct self-assembly of cyclic dimeric complexes. The isolation and characterization of eight oligomeric species from this one pot reaction, as well as the photo-switching behaviour of some of these compounds, are discussed in this Chapter.

The next phase of this research was focused on rotaxanes because of their crucial role in the development of molecular devices. In particular, isomeric rotaxanes, generally resulting from the capping of an inclusion complex between an asymmetric macrocycle and a mono-capped guest, can exhibit different properties depending on the orientation of the host. Chapter 3 describes a complementary synthetic approach based on the desymmetrization of a pre-formed rotaxane. This work includes the synthesis of an alpha-CD [2]rotaxane and the subsequent preparation, separation and characterization of bromine-functionalised orientational isomers.

Finally, the behaviour of cyclodextrin-based rotaxanes as insulated molecular wires is investigated in Chapter 4. This work involved the discovery of the conductivity behaviour of crystals of two different alpha-CD rotaxanes showing pi-pi stacking aggregation in solution and in solid phase. The comparison with a blank experiment consisting of an alpha-CD crystal, the investigation of insulating properties of one of the rotaxanes, and some preliminary co-crystallisation experiments are also discussed as part of this study. This work identified the ability of self-assembled arrays of cyclodextrin-based rotaxanes to act as insulated molecular wires resembling coaxial cables.

Overall, this Thesis describes new synthetic approaches to prepare daisy chain oligomers and [2]rotaxanes and develops their respective abilities to act as molecular muscles and microelectronic devices.