Tunable molecular packing modes via H- or J-aggregates in the supramolecular helical nanostructures from an achiral C 3 symmetric molecule

The self-assembly of a -symmetric molecule benzene-1,3,5-tricarboxylate substituted with methyl cinnamate (BTECM) has been investigated by a reprecipitation method in H O 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 molecule BTECM. More importantly, the helices aggregated different packing modes in H O and CTAB aqueous solution. In H O, the nanostructures underwent a process of particles, fibers and helices 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 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.