Tunable molecular packing modes via H- or J-aggregates in the supramolecular helical nanostructures from an achiral C3 symmetric molecule

Abstract

The self-assembly of a C₃-symmetric molecule benzene-1,3,5-tricarboxylate substituted with methyl cinnamate (BTECM) has been investigated by a reprecipitation method in H₂O and cetyltrimethylammonium bromide (CTAB) aqueous solution, respectively. The nanostructures and characteristics of the assemblies were monitored by UV-Vis spectroscopy, fluorescence (FL) spectroscopy, circular dichroism (CD) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that helical nanostructures were successfully assembled from the achiral C₃ molecule BTECM. More importantly, the helices aggregated via different packing modes in H₂O and CTAB aqueous solution. In H₂O, the nanostructures underwent a process of particles, fibers and helices via H-type aggregate upon aging. In the case of CTAB aqueous solution (1.2 mM), the helices were translated from particles and the molecules were inclined to aggregate via the J-type mode. In addition, the aggregation process could be accelerated by raising the temperature proved by UV-Vis spectra. A molecular aggregation mechanism was proposed based on the experimental results.