Figure 2 Changes in CD and UV-vis spectra of the CABu/PMMAzo-1 composite films (CABu/PMMAzo-1 = 2:1, w/w) (a) before annealing as prepared films at room temperature and (b) after termal annealing at 80 °C for 10 min. (c) A comparison of g CD values at the first Cotton band (350–400 nm) in three composite films prepared by chloroform (red), dichloroethane (green), and tetrahydrofuran (blue) before and after the annealing processes. (d) Possible supramolecular stacking structure of PMMAzo.
Besides, the relative weight ratios of CABu to PMMAzo significantly affect g CD values (entries 2, 5-7 in Table 1). From Figure 3a, it is evident that all the polymer composite films showed very strong Cotton effects at room temperature in the absorption region of the trans -azobenzene group, demonstrating that the CABu successfully induced the helical π-stacks of Azo building units in polymer side-chains. Further annealing increased the CD amplitude by two orders of magnitude (Figure 3b). The correspondingg CD values were summarized in Figure 3c, the maximum g CD values of each polymer films decreased gradually with the increase of CABu content. This may be attributed to the fact that proper content of inducer helps to form a more regular surface, because we found that more inducer would make the film inhomogeneous (Figure 4d). Apparently, the preference for induced supramolecular chirality can be tuned by changing the content of chiral semi-synthetic biomaterials or the type of solvent.