Synthesis and properties of supramolecular gels based on tetrathiafulvalene and cyanobiphenyl units

For the development of self-assembly donor-σ-acceptor (D-σ-A) molecules, a series of D-σ-A low-molecular mass organogelators, consisting of tetrathiafulvalene (D) and cyanobiphenyl (A) connected by a thioalkanoyloxy spacer of varying lengths modified with hydrophobic chains incorporating amide groups on the side, was designed and readily synthesized. Their gelation properties were studied. The results showed that the gelation capability of these compounds was highly dependent on the alkyl chain length in the spacer group and the TTF and cyanobiphenyl units. Derivative 1a with short alkyl chain (n = 4) efficiently gelated in some aromatic solvents, forming opaque organogels. These gelators reacted with F4TCNQ to form stable charge-transfer complex gels in ethanol. Clear evidence of self-assembled micro/nanoflower, fibrous, or tubular morphologies in gelation state was obtained by scanning electron microscopy. It was found that the molecules adopted lamellar and rectangular columnar molecular packing models in the gel phase by X-ray diffraction. The native gels underwent a reversible gel-sol phase transition upon exposure to external stimuli. The gel-sol transition of the organogel was stimulated by the addition of fluoride anions. Interestingly, all gels showed an irreversible gel-sol transition triggered by TFA and TEA. The formation of flower-like morphologies of TTF-based derivatives in the gel state was observed.