Photoresponsive Mechanically Interlocked [ a n]Daisy Chain Network

Abstract Muscle integrates molecular-machine motion with hierarchical structural organization, enabling it to sustain large deformations under physiological loads. Mechanically interlocked molecules offer a versatile platform to mimic such molecular-level motion, but efficiently translating it into macroscopic material performance, akin to muscle, remains challenging. Herein, we report a mechanically interlocked network (MIN) with [an]daisy chain backbone which can efficiently scale up the photoresponsive behavior of mechanical bonds, exhibiting intelligently tunable mechanical properties. In specific, photoresponsive unit of arylazopyrazole (AAP) is embedded onto the axis of each mechanical bond in the [an]daisy chain backbone. Ultraviolet light triggers the trans-to-cis (E/Z) isomerization of the AAP moieties, and when amplified through the [an]daisy chain backbone, it brings about significant changes in the material’s properties. On one hand, the E/Z isomerization significantly shortens the dimension of the [an]daisy chain framework, resulting in a notable increase in the material modulus (from 1.6 to 4.0 MPa). On the other hand, the cis configuration of AAP formed after the isomerization restricts the mobility of the mechanical bonds, resulting in a shorter elongation at break (from 343% to 272%). Our work presents an efficient method for amplifying mechanical bond responsiveness, providing a fresh perspective for the development of intelligent materials.