Researchers have demonstrated that two particular organic molecules — one electron-rich, the other electron-deficient — can co-assemble1 in solution to form a fluorescent hydrogel. This hydrogel, composed of a network of very long nanofibres, may have potential applications in the field of organic and supramolecular electronics.
Donor–acceptor pairs have been used as the basis for hydrogel formation for many years, but only now have researchers exploited the chromophores (the parts of a molecule that determine its colour) of the constituent molecules.
To exploit the potential of such chromophores, which respond to stimuli such as light, the researchers synthesized a donor–acceptor pair comprising coronene tetracarboxylate tetrapotassium salt (CS) and a dodecyl-functionalized methylviologen derivative (DMV). They mixed a solution of DMV in methanol with an aqueous solution containing free CS molecules.
A charge-transfer complex was created between the electron-donating CS and the electron-accepted DMV, and this allowed any changes in absorption and emission properties to be seen with the naked eye.
The resulting CS–DMV hydrogel was stable for several months, and was composed of an entangled network of very long fibres 10–15 mm in length and 100–300 nm in diameter. In addition, the one-dimensional charge-transfer nanofibres formed from CS and DMV were found to exhibit better conductivity than nanofibres made from 'traditional' donor–acceptor polymers.
"The embedded fluorescent chromophores in the hydrogels can be exploited for sensory applications," says lead researcher Subi J. George from the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore.
