Supramolecular Polymerization of C3-Symmetric Organogelators: Cooperativity, Solvent, and Gelation Relationship

A systematic study of the influence of solvent and the size of C3-symmetric discotics on their supramolecular polymerization mechanism is presented. The cooperativity of the self-assembly of the reported compounds is directly related to their gelation ability. The two series of C3-symmetric discotics investigated herein are based on benzene-1,3,5-tricarboxamides (BTAs) and oligo(phenylene ethynylene)-based tricarboxamides (OPETAs) that are peripherally decorated with achiral (1a and 2a) or chiral N-(2-aminoethyl)-3,4,5-trialkoxybenzamide units (1b and 2b). The supramolecular polymerization of compounds 1a,b and 2a,b has been exhaustively investigated in a number of solvents and by using various techniques: variable-temperature circular dichroism (VT-CD) spectroscopy, concentration-dependent 1HNMR spectroscopy, and isothermal titration calorimetry (ITC). The supramolecular polymerization mechanism of compounds 2 is highly cooperative in solvents such as methylcyclohexane and toluene and is isodesmic in CHCl3. Unexpectedly, chiral compound 1b is practically CD-silent, in contrast with previously reported BTAs. ITC measurements in CHCl3 demonstrated that the supramolecular polymerization of BTA 1a is isodesmic. These results confirm the strong influence of the -surface of the central aromatic core of the studied discotic and the branched nature of the peripheral side chains on the supramolecular polymerization. The gelation ability of these organogelators is negated in CHCl3, in which the supramolecular polymerization mechanism is isodesmic.