Oligo[n]ammonium dumbbells containing a specific number of �(CH2NH2+ CH2)� repeating units have been used to template the quantitative assembly of oligo[n]rotaxanes that present an discrete number of aromatic crown-ether rings spaced approximately 3.4 � apart, a distance ideal for strong p�p stacking interactions as verified by single crystal X-ray analysis of a [3]- and [4]rotaxane. Functionalization of these rings with additional aromatic units renders co-facially stacked single molecule arrays of the functional units, as determined by NMR spectroscopy and X-ray crystallography, and offers an opportunity for long-range p-orbital interactions to occur along the long axis of the molecule. Taking advantage of this geometrical feature, we have prepared a series of oligo[n]rotaxanes modified with redox-active naphthalene diimide (NDI) moieties to afford 1-D arrays of the n-type unit in order to explore their potential to serve as through-space electron sharing models and �molecular wires.� Utilizing both cyclic voltammetry and EPR/ENDOR spectroscopic techniques, we show that these co-facial assemblies are capable of electron sharing with only a moderate loss in transport as the number of NDI units is increased, where the sharing events are gated by the flexibility of various co-conformations that can be adopted by the oligo[n]rotaxane. By employing template-directed synthesis, dynamic covalent chemistry and mechanical bond formation, we have been able to (i) avoid the uncontrolled assembly of molecular components which can ultimately limit the size of a system and produce ambiguous results and (ii) study systematically the effects of monomer organization over a discrete transport length on the efficiency of electron sharing. Looking forward, these results are expected to contribute to the design of more efficient through-space electron transfer models and raise consideration of mechanically interlocked molecules as active materials in organic electronic devices.

Electron sharing processes within dynamically self-assembled arrays

248th National Meeting (2014)

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