Sylvie Drayss‐Orth

Abstract The synthesis and characterization of zwitterionic molecular [ c 2]‐ and [ a 2]‐daisy chains are described, relying on recognition of a positively charged cyclophane and a negatively charged oligo(phenylene‐ethynylene) (OPE) rod in aqueous medium. For this purpose, syntheses of an acetylene‐functionalized macrocyclic receptor and a water‐soluble OPE‐rod as the guest component are presented, from which a heteroditopic daisy chain monomer was prepared. This monomer aggregated strongly in water/methanol 4:1 and formed molecular daisy chains, which were isolated as interlocked species from a stoppering reaction at 1 m m concentration. The cyclic dimer [ c 2] was the main product with an isolated yield of 30 % and consisted of a mixture of diastereomers, as evidenced by 1 H NMR spectroscopy.

Two [2]rotaxanes have been assembled in water from modular subunits through Cu I ‐catalyzed azide–alkyne “click” chemistry. For this purpose, 2,6‐disubstituted naphthalene axles with solubilizing oligo(ethylene glycol) (OEG) chains ( n = 1–5) and propargyl terminal groups were synthesized and examined for their propensity to form inclusion complexes with a dicationic Diederich‐type cyclophane host. The dependence of pseudorotaxane formation on the linkers between the naphthalene core and OEG chains, and in the case of ester linkers on different spacer lengths, was analyzed by titration experiments. In addition, the inclusion complexes of two [2]rotaxanes were trapped by using a water‐soluble azide‐functionalized stopper. Repetitive chromatography finally enabled the isolation of both mechanically interlocked [2]rotaxanes.

Structurally diverse rotaxane-based systems have been investigated extensively for applications as molecular machines and functional nanomaterials. Although the vast majority of functional molecules were assembled and function in organic solvents, to date the most efficient and sophisticated molecular machines are biomolecules which function in aqueous media. Many vital processes, such as protein folding and assembly, rely on hydrophobic interactions and are only possible in aqueous environment. From a supramolecular chemistry perspective, the hydrophobic effect is an appealing driving force for host-guest association as it potentially leads to high complexation affinities and no extra binding sites need to be installed into the respective components. Appealing macrocyclic candidates for the preparation of mechanically interlocked molecules in aqueous media are the synthetically modifiable, water-soluble cyclophanes developed and comprehensively studied by Diederich et al..
\n The focus of this doctoral thesis was to identify suitable guest molecules for Diederich-type cyclophanes, allowing for the assembly of rotaxanes and also molecular daisy chains. The first part of the thesis describes the investigation of the aggregation behavior of amphiphiles based on OPE guests which are potentially capable of forming molecular daisy chains (Chapter 2). A deeper insight into the system was obtained through a series of rotaxane model compounds, basically relying on the main components of the previously examined amphiphiles (Chapter 3). The investigation of an extended scope of potential guest molecules via 1H NMR complexation studies resulted in an optimization of the molecular guest design and revealed some important features of suitable candidates (Chapter 4). Based on these results a water-soluble 2,6-disubstituted naphthalene derivative was found to function as (pseudo)rotaxane axle and enabled the isolation and characterization of a [2]rotaxane (Chapter 5). The results obtained throughout this doctoral thesis allow to obtain guidelines for the successful preparation of interlocked molecular daisy chains.