Mechanophore activation enhanced by hydrogen bonding of diarylurea motifs: An efficient supramolecular force-transducing system

Abstract

Macromolecules are efficient as mechanical transducers for mechanically induced chemical bond cleavage reactions. Although various classes of polymers have been studied as effective mechanical-force transducers for mechanophores, alternatives to polymer chains, that is, small molecules, have rarely been studied. In this paper, the role of hydrogen bonding as small-molecule mechanical-force transducers for the activation of mechano-responsive molecular units (mechanophores) in the bulk is investigated. The introduction of diarylurea linkage motifs, which are known as strong hydrogen bonding groups, enhances the mechanochemical activation of the fluorescent mechanophore tetraarylsuccinonitrile (TASN) as effectively as the attachment of a typical macromolecular transducer. Electron paramagnetic resonance measurements of mechanically activated TASN with diphenyl urea motifs demonstrate its higher carbon–carbon bond dissociation ratio compared to that of TASN without diphenyl urea motifs. This efficient supramolecular-force-transducing system represents a new concept in the field of mechanochemistry, namely, the enhancement of mechanochemical bond scission by simply changing the substituents of a mechanophore, even in small molecules.