[2.2]Paracyclophane molecular scaffolds ([2.2]pCps) have been of utmost interest for fundamental research due to their stereochemistry, unique reactivity, and optical properties. Various [2.2]pCp scaffolds have been previously exploited as components of charge-transfer complexes, through-space donor-acceptor systems, and conjugated polymers. In the supramolecular context, our group reported the first monomer based on [2.2]pCps – [2.2]paracyclophane-tetracarboxamide ([2.2]pCpTA) – capable of forming supramolecular polymers. The [2.2]pCpTA monomer self-assembles to form homochiral 1-D stacks composed of double-helical hydrogen bonding arrays through anti- aligned amides. Subtle changes in monomer structure, such as bridge expansion, heteroatom inclusion in the bridge, and changes in amide connectivity, alters the assembly strength and thermodynamics. To develop additional structure-activity relationships, the consideration of alternate H-bonding units is crucial. Here we present two new classes of self-assembling [2.2]paracyclophanes with different hydrogen bonding units, [2.2]paracyclophane-tetraurea ([2.2]pCpTU) and [2.2]paracyclophane-tetracarbamate ([2.2]pCpNTC). The compounds have been synthesized and characterized in the solid state by single-crystal X-ray diffraction, and in solution by FT-IR and NMR experiments. The studies reveal that under optimized conditions the [2.2]pCpTU monomer assembles aggressively, consistent with its additional H-bonding capability. However, exchange of -NH for an oxygen to give the [2.2]pCpNTC monomer leads to an unprecedented change in the H-bonding directionality and π-stacking geometry of the assemblies.

Programming the self-assembly of [n.n]Paracyclophanes with carbamate and urea units

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