Pyrene-functionalized organogel and spacer effect: from emissive nanofiber to nanotube and inversion of supramolecular chirality

Two pyrene-functionalized gelator molecules were designed, in which the pyrene moiety was linked to amphiphilic L-glutamide directly (PyC0) and with three methylene spacers (PyC3), respectively. Both of the compounds can form strong fluorescent organogels in polar and nonpolar solvents. Depending on the spacer, the pyrene gels showed different fluorescence. During the gel formation, the chirality in the L-glutamide moiety was transferred to the self-assembled nanostructures, and the expression of the chirality at a supramolecular level was related to both the spacer and solvents. While the PyC3 gels showed the same P-chirality both in the polar and nonpolar solvents, the PyC0 gel displayed chirality inversion in polar and non-polar solvents, i.e. M-chirality in non-polar solvents and P-chirality in polar solvents. Interestingly, although both compounds self-assembled mainly into nanofibers in toluene, PyC0 self-assembled into nanotubes in DMSO. It was suggested the H-bonding between the amide groups and the pi-pi stacking between the pyrene moieties contributed to the formation of the gels, while the spacer between the amide groups and the pyrene ring regulated the two interactions, and thus influenced the assembly mode as well as the corresponding supramolecular chirality.