UV- and Thermo-Controllable Azobenzene-Decorated Polycarbodiimide Molecular Springs

Molecular switches offer wide applicability through conformational changes which can be triggered by external stimuli. Azobenzenes are excellent candidates to contribute toward a rational design of molecular switches because they exist as either cis or trans isomers as a result of the dynamic photoisomerization process. In this study, we leverage the azobenzene stimuli response by attaching it as a pendant group on polycarbodiimides synthesized using screw sense polymerization. The exposure of the polymer sample in solution to UV light induces the transformation of the azobenzene pendant groups to the cis isomer with re-emergence of the trans conformer under visible light or heat. Corroborating experimental and computational data reveal that these events induce spring-like expansion-contraction motions throughout the helical backbone. Our finding suggests the use of polycarbodiimide-derived photoswitches as dynamic materials in biological applications and materials science.