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