Multi-Responsive Supramolecular Gels Based on Charge Transfer Interactions

We report the co-assembly of aromatic donor (D) and acceptor (A) molecules into purple sponge-like supramolecular gels through susceptible charge transfer interactions with the aid of solvophobic interactions. The gel remained intact with the addition of up to 23 % (v/v) of nonpolar good solvents, such as toluene and xylene, but dissociated in the presence of <2 % (v/v) of polar solvents, such as tetrahydrofuran, ethyl acetate, and alcohols, with highly distinguishable changes of color. Notably, the gel dissolved within 1 min and the solution turned blue when 0.1 % (v/v) of methanol was added. The response to trifluoroacetic acid was extremely sensitive (i.e., the gel vanished immediately in the presence of 2 equivalents of trifluoroacetic acid), and the subsequent addition of trimethylamine could recover the purple gel. The multiple and visible response thus render the D-A gels as a potential detector for sensing complex chemical environments.