Scheme 2 Proposed models of (left) chiral C-H/O=C and C-H/π interactions between D-Glu and PMMAzo polymers and (right) π-π stacks of side-chain Azo building blocks.
Conclusions
In summary, chirality induction of achiral azobenzene-containing polymer films by natural cellulose derivatives was systematically studied. The induced circular dichroism of the polymer composite films can be tuned by adjusting the annealing treatment, the content of the chirality-inducing scaffolding and the molecular weight of the Azo polymer. Meanwhile, a chiroptical switch with more than five cycles can be successfully constructed by the trans -cis isomerization of azobenzene units. By using the basic repeating units of cellulose, permethylated D-Glu and L-Glu, the mechanism of chiral induction and transfer was elucidated. Chirality transferred from the chiral semi-synthetic biomaterials to polymer domains and induced the aggregation chirality of the achiral side-chains through C-H/O=C and C-H/π interactions between glucose repeating units and PMMAzo polymers. Using cellulose that are widely distributed in nature to induce strong circular dichroism in achiral polymers, this work provides an elegant and facile method to transfer chirality between host and guest substances, which facilitates the further functionalization of chiroptical polymer materials with manipulatable properties.
Experimental