Conformational analysis of supramolecular polymerization processes of disc-like molecules

Abstract

N,N′,N′′-Trialkylbenzene-1,3,5-tricarboxamides (BTAs) cooperatively self-assemble into one-dimensional, helical supramolecular polymers in apolar alkane solutions. Previous studies revealed that the position and configuration of the methyl group on the aliphatic side-chain gives rise to an ‘odd–even effect’ both in the shape and the sign of the CD-effect. In this study, we elucidate the molecular origin of this odd–even effect by a combination of TD-DFT calculations and spectroscopic experiments. In addition, we observed a pronounced effect of the molecular structure of the alkane solvent on the shape of the Cotton effects and the thermodynamic parameters describing the cooperative supramolecular polymerization. The results revealed a different ability of solvent molecules governed by the shape of their structure to intercalate into the helical stacks, which influences the conformation of the monomer within the supramolecular polymer. The solvent affects the dihedral angle (θ) between the CO group and the benzene central core of the BTA molecule. These findings help to increase a molecular-level understanding of how the solvent controls the conformation of repeating units in a supramolecular system.