Tunable Thermochromism of Multifunctional Charge-Transfer-Based Supramolecular Materials Assembled in Water

Stimuli-responsive materials, such as thermochromics, have found mass usage and profitability in manufacturing and process control. Imparting charge-transfer-based functional supramolecular materials with tunable thermochromism emerges as an ideal strategy to construct optically responsive multifunctional assemblies. Herein, the authors report a new series of thermochromic charge-transfer-based supramolecular materials assembled in water. These assemblies are composed of a bis-bipyridinium-derived acceptor and a series of commercially available donors - namely, the neurotransmitter melatonin and its analogue bioisosteres. When the chemical structure of the donors are tailored, the strength of the charge-transfer interactions can be tuned. Thermochromic aerogels and inks of these materials are prepared, with a large selection of colors, in environment-friendly solvents and demonstrate tunable thermochromic transition temperatures ranging from 45 to 105 °C. Favorable compatibility of these materials with commercial inks and inkjet printers afford excellent pattern quality with extended color options. Mechanistic studies reveal that the two types of water molecules were bound to the supramolecular complexes with differing strengths, and that the more weakly bound water is responsible for the thermochromic transitions.