Figure 1 . Changes in CD and UV-vis spectra of the composite
films consisiting of CTA/PMMAzo-1 (1:1, w/w, red curves) and
CABu/PMMAzo-1 (1:1, w/w, blue curves, entry 5 in Table 1) (a) before (as
prepared films at room temperature) and (b) after termal annealing
process at 80 °C for 10 min.
We therefore investigated the effect of annealing time on the induction
of the chiral supramolecular structure of polymer films. As shown in
Figure S4, a 10-minute annealing treatment of the polymer composite film
is enough to obtain a 10-fold increase in maximum helicity over the
pristine one (entries 1-4). Furthermore, the solvent used to dissolve
the polymer is the key for aggregation processes and can strongly
influence aggregation behavior via the specific interactions between
solvent and solute. On the one hand, the basic features of solvents such
as polarity, viscosity, and solubility for the polymers could affect the
interaction tendencies between building blocks of supramolecular
systems. According to our previous works,7, 29, 30 the
types of solvents played an important role in the supramolecular
assembly of azobenzene-containing polymers. For example, supramolecular
chirality of azobenzene-containing polymers can be constructed in
chloroform, dichloromethane and 1,2-dichloroethane, but cannot inN ,N -dimethylformamide.29 Furthermore,
the chiral expression of supramolecular aggregates also differs in
different solvents. On the other hand, supramolecular chirality is
produced by nonsymmetric arrangement of building blocks through weaker
noncovalent bond interaction, which can be easily influenced by external
environmental factors such as solvents, which is generally dynamic,
changing in response to external stimuli.31 Here, CABu
and PMMAzo-1 were co-solved in chloroform (CHCl3),
dichloroethane (CH2Cl2) and
tetrahydrofuran (THF) with the mass concentration of 30 mg/mL, and
solvent polarity is also an important factor determining the chiral
expression of composite films. When the solvent for dissolving the
mixture was changed from CHCl3 to
CH2Cl2 and THF, there was a more
significant increase in chiral expression regardless of the annealing
treatment (Figures 2a and 2b). The g CD of the
spin-coated film prepared by THF solvent is the largest among all series
(Figure 2c). These results indicate that THF is the best solvent for
dissolving polymers, and its appropriate polarity can effectively
promote the cooperative interaction between polymer building blocks and
chiral CABu semi-synthetic biomaterials (Figure 2d).