Making and Breaking: Supramolecular Chirality Modulation via Stepwise Assembly and Disassembly of Nano-Size...

A molecular-level understanding of supramolecular chirality amplification and attenuation is established through the coordination-driven self-assembly of a 'nano-size' achiral Zn(II)porphyrin trimer (host) and a series of chiral diamino esters (substrates). The processes occur through the stepwise formation of polymer and dimer via intermolecular assembling and disassembling processes, respectively. Crystallographic characterizations of both the polymer and dimer allow systematic scrutiny of their structural changes, elucidating their chiroptical properties. The electronic circular dichroism (CD) spectra display opposite signs for the R and S substrates in both the polymer and dimer, indicating that the chirality of the complexes are dictated solely by the absolute configuration of the substrate. In the dimer, both intra- and intermolecular couplings were identified while in the polymer, CD signals were significantly amplified, owing to cumulative intermolecular couplings. DFT and TDDFT studies corroborate these experimental findings and provide valuable insights into the origin of the chiroptical responses, amplification and reduction in these systems.