Supramolecular electroactive organogel and conducting nanofibers with C3-symmetrical architectures

Abstract

Two C₃ symmetric tris(TTF) derivatives, based on a central unit containing the rigid core 1,3,5-tricarbonyl-benzene substituted with three 3,3′-diamino-2,2′-bipyridines, have been synthesized by a convergent strategy. Single crystal X-ray analysis of the precursor 3′-[(ethylenedithio-tetrathiafulvalenyl)formylamino]-2,2′-bipyridine-3-amine shows a planar transoid conformation for the bipyridine unit, favored by intramolecular hydrogen bonding. The compound N,N′,N″-tris{3[3′-[bis(ethylthio)-tetrathiafulvalenyl]formylamino]-2,2′-bipyridyl}-benzene-1,3,5-tricarboxamide, having C₃ symmetry, presents gelator properties in chlorinated solvents. The gel formed in ortho-dichlorobenzene provided—after evaporation of the solvent—a xerogel constituted by a complex network of thick and thinner fibers as demonstrated by TEM and AFM microscopies. The thick fibers were about 100 nm wide and between 1 and 5 µm long, and the thinner ones between 12 and 18 nm wide and 50 to 500 nm long. Iodine doping of the material induced the formation of a mixed valence system with charge transfer, as indicated by IR-NIR spectroscopic measurements. The doped material has a TTF:I₃ ratio of 2.4:1 ten minutes after doping, but slowly loses iodine over days. The morphology of the gel did not change after the doping process, as revealed by SEM and AFM experiments. Current sensing AFM measurements showed that the thicker fibers are more conducting than the thinner ones, a likely consequence of the better ordering and/or more effective interfiber contacts in the former.