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

Abstract

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.

Columnar Liquid Crystalline Corannulenes: Synthesis, Assembly and Charge‐Carrier Transport Properties

“…[ 13 ] Upon irradiation with 365 nm UV light, the intense peak at 373 ( 1a ) or 375 nm ( 1b ), which was observed at room temperature, shifted to a shorter wavelength of 362 ( 1a ) or 365 nm ( 1b ), and the intensity decreased due to the hypsochromic effect. [ 14 ] The electronic n‐π* transition only appeared in cis isomers, and the characteristic band at 463—465 nm was indicative of the formation of the cis isomer upon UV irradiation. Additionally, irradiation of the two compounds at 365 nm caused the trans to cis isomerization (Figure 2).…”

Stimuli-responsive Molecular Springs Based on Single- and Multi-stranded Helical Structures

“…89,95 Novak and co-workers reported a cis-trans isomerizationtriggered molecular spring utilizing an optically-active poly-(carbodiimide) derivative (37) bearing photo-responsive azobenzene pendants prepared from the helix-sense-selective polymerization of the corresponding achiral carbodiimide monomer with a chiral BINOL-Ti(IV) initiator (BINOL = 1,1¤-bi-2naphthol). 96 The excess helical sense-biased 37 exhibits reversible springlike extension and contraction motions through reversible trans-to-cis and cis-to-trans isomerizations of the pendant azobenzene groups induced by the UV irradiation at 365 nm and the thermal annealing at 40°C, respectively, while maintaining the original helix-sense excess, as revealed by optical rotation and IR studies in combination with molecular dynamics simulations.…”

Highly Regioselective and Helix-Sense Selective Living Polymerization of Phenyl and Alkoxyallene Using Chiral Nickel(II) Catalysts

“…Helix is one of the most important secondary structural motifs in biopolymers and also in synthetic macromolecules. − The one-handed helical conformation adopted by biological macromolecules such as protein and DNA plays important living functions including molecular recognition, catalysis, inheritance, replication, and so on. − A slight damage on the helical structure of biomacromolecules can cause a variety of severe diseases. For example, misfolding the helix of proteins into an extended β-sheet may result in amyloid structures accompanied by grievous dysfunctions including Alzheimer’s disease, Parkinson’s disease, and diabetes. , Therefore, stimulated by the biological helices and functions, synthetic helical polymers have attracted great attention from synthetic chemistry to materials science and biological engineering. − These research studies not only explore the structure and property of the unique helices in nature but also develop new materials with novel functions. − Moreover, the study on a helical polymer can bring out a new structural platform for the development of novel functional materials. − Although the helical polymer is still on the preliminary research stage, it has exhibited a wide range of applications, such as those in enantiomer separation, chiral switch, asymmetric catalysis, circularly polarized luminescence (CPL), and optoelectronic devices among others. − From the reported helical polymers, polyallene is of particular interest because it contains reactive exo -double bonds along the backbone which can be further decorated with other intriguing functionalities. , Polyallene is generally produced through the radical polymerization or coordination polymerization of the corresponding allene monomers using transition-metal complexes as catalysts. , The living/controlled coordination polymerization can yield polyallenes with expected molecular mass and low polydispersity. , However, both the accumulated double bonds of allene monomers can be polymerized and result in polyallene with complex architectures. − Thus, developing a new method for living/controlled polymerization of allene monomers with high regioselectivity of the accumulated double bonds is greatly desired.…”