Supramolecular Oligourethane Gel with Multicolor Luminescence Controlled by Mechanically Sensitive Hydrogen-Bonding

We report a new type of mechanically sensitive multicolor luminescent oligourethane gel (OUA-gel). The conformation of the oligomeric chains can be controlled by changing the strength of hydrogen bonds. The optical properties of the oligomers are highly dependent on the conformations which vary in response to mechanical stresses and phase transitions. The design relies on the introduction of a single mechanical chromophore, aurintricarboxylic acid, with propeller-like, spatially crowded, and highly twisted conformations, and the presence of three carboxyl groups, which provide multidirectional hydrogen-bonding opportunities. Introducing dimethylsulfoxide (DMSO) as an additional H-bond acceptor molecule leads to a viscous OUA-gel which exhibits multiemission colors because of changes in the chain conformation within the matrix, which are induced by different strengths of H bonds. The conformation can be adjusted by mechanical force or temperature, both of which influence the H-bonding. The multifunctional and multicolored mechanochromism of the OUA-gel has great promise in sensing applications. The results represent a substantial step toward understanding the mechanism of polychromism in soft materials and the molecular design of advanced smart materials.