The mechanism by which monomers in solution, beyond a certain concentration or below a certain temperature, self-assemble to form one dimensional supramolecular polymers determines much of the bulk properties of the polymer.

Reported here is the synthesis, characterization, and isodesmic supramolecular polymerization of [3.3]­paracyclophane-5,8,14,17-tetracarboxamide ([3.3]­pCpTA). The self-assembling monomer, a bridge-expanded homolog of [2.2]­paracyclophane-4,7,12,15-tetracarboxamide ([2.2]­pCpTA), forms homochiral assemblies in nonpolar solution and the solid state through double-helical intermolecular and transannular hydrogen bonding. The additional methylene unit in the [3.3]­paracyclophane bridge results in a weakened supramolecular assembly for [3.3]­pCpTA compared to [2.2]­pCpTA in solution. Likely origins of the change in assembly strength, revealed through X-ray crystallography, computational analysis, and solution-phase spectroscopy, are an increase in (a) the intramolecular and intermolecular deck-to-deck spacing compared to [2.2]­paracyclophane resulting from larger amide dihedral angles accompanying transannular hydrogen bonding in the [3.3]­paracyclophane and (b) monomer entropy associated with the scissoring motion of the [3.3]­paracyclophane bridge.

A series of [2.2]paracyclophane‐bisamide regioisomers and alkylated comparators were designed, synthesized, and characterized in order to better understand the transannular hydrogen bonding of [2.2]paracyclophane‐based molecular recognition units. X‐Ray crystallography shows that transannular hydrogen bonding is maintained in the solid‐state, but no stereospecific self‐recognition is observed. The assignment of both transannularly and intermolecularly hydrogen bonded N−H stretches could be made by infrared spectroscopy, and the effect of transannular hydrogen bonding on amide bond rotation dynamics is observed by 1H‐NMR in nonpolar solvents. The consequences of transannular hydrogen bonding on the optical properties of [2.2]paracyclophane is observed by comparing alkylated and non‐alkylated pseudo‐ortho 4,12‐[2.2]paracyclophane‐bisamides. Finally, optical resolution of 4‐mono‐[2.2]paracyclophane and pseudo‐ortho 4,12‐[2.2]paracyclophane‐bisamides was achieved through the corresponding sulfinyl diastereoisomers for circular dichroism studies. Transannular hydrogen bonding in [2.2]paracyclophane‐amides allows preorganization for self‐complementary intermolecular assembly, but is weak enough to allow rapid rotation of the amides even in nonpolar solvents.

The iterative association of monomer units through noncovalent interactions often leads to chiral supramolecular polymers. Monomers comprising these materials can be further divided into those with chiral centers and those without. The latter class is often less studied but attractive since it features monomer designs with chirality at the core rather than the periphery of the molecules. In this mini-review, we summarize the existing strategies to construct supramolecular polymers from chiral molecules with no chiral centers and offer perspectives on fundamental trends and differences between them and their counterparts with chiral centers.

The supramolecular polymerization of 2,11-dithia[3.3]­paracyclophanes through self-complementary intermolecular and transannular amide hydrogen bonding is presented. An n → π* interaction between the amide hydrogen bonding units and the central bridging atom results from the single-point exchange of a carbon atom for a sulfur atom. This orbital donor–acceptor interaction can be strengthened by oxidizing the sulfide to a sulfone which acts to shorten the donor···acceptor distance and increase orbital overlap. Experimental signatures of the increased n → π* interaction include larger isodesmic polymerization elongation constants in solution, changes in characteristic bond stretching frequencies, and geometric/structural changes evaluated by X-ray crystallography. The experimental data are supported by extensive computational investigations of both assembling and nonassembling 2,11-dithia[3.3]­paracyclophanes as well as a rationally designed model system to confirm the role of stereoelectronic effects on supramolecular polymer assembly.