a Determined by GPC according to PS standards in THF. b Mass ratio of CABu to PMMAzo polymer (w/w). c Annealing time at 80oC. dg CD value at the first Cotton band (350–400 nm).
From Figure 1a, two absorption bands of the film are detected in the UV-vis spectra. The π-π* transition of trans -Azo is responsible for the strong absorption band between 320 nm and 400 nm, while the n-π* transition of cis -Azo underlies the weak absorption band between 430 nm and 500 nm.28 Achiral polymer films naturally do not have a CD signal, obviously, the CD signal at 300–450 nm can be observed when cellulose was mixed into the PMMAzo-1 polymer film (entry 1). A positive CD signal at around 390 nm was induced by CTA while a negative CD was induced by CABu, associated with the zero-cross-point at 350 nm (Figure 1a). The excitonic couplet at 350 nm in the Cotton band may originate from the splitting of an H -band that corresponds to a chiral interaction of H -aggregation among neighboring Azo chromophores. This interaction could lead to helical rotation within the nematic phase, producing optically active polymer films. Subsequent annealing of the polymer film at 80 °C for ten minutes could result in a tenfold increase in the CD amplitude, without changing the sign of CD signal (Figure 1b). Annealing process can promote the formation of chiral supramolecular structures by inducing molecular rearrangements and enabling intermolecular interactions. By heating the film to its LC phase temperature for a period of time, annealing can increase the molecular mobility, reduce impurities and defects, and facilitate the ordering and alignment of mesogens.