Curvature-emergent supramolecular polymerization of a porphyrin dyad with a scissor-shaped motif

Abstract

Curvature has recently emerged as a key structural parameter that dictates the pathway and topology of supramolecular polymerization. We previously showed that scissor-shaped azobenzene dyads, dimerized through a xylylene spacer bearing long alkyl chains, undergo folding-induced self-assembly to yield curvature-derived architectures such as nanorings and nanotubes. Here we extend this scaffold to a bulkier chromophore and demonstrate that the curvature-directed pathway is preserved. Dimerization of tetraphenylporphyrin on the scissor-shaped backbone yields a molecule that, in nonpolar solvents, exhibits a split, bathochromically shifted Soret band. This finding suggests intra- and intermolecular J-type exciton coupling during folding-induced supramolecular polymerization. AFM revealed the formation of helically coiled supramolecular polymers (helicoids). These helicoids evolve into nanotubes over time; applying sonication beforehand induces fragmentation that closes the curved segments into discrete toroids.