Tunable Chiroptical Response in Helically Stacked Multilayers of Achiral Polythiophene

Multilayered films composed of uniaxially aligned polythiophene layers stacked with controlled rotational offsets around the film normal were fabricated via a film transfer process. Although the polymer itself is achiral, the resulting multilayer structures exhibit structural helical chirality. The films show pronounced circular dichroism (CD) in the visible region, with both the intensity and sign systematically tunable by the number of layers, twist angles, and handedness of stacking. Ion-exchange doping further extends the CD response into the near-infrared region through polaron absorption. Optical simulations based on Mueller matrix analysis quantitatively reproduce the experimental CD spectra, thereby providing general design principles for tuning chiroptical responses. The simulations predict that insertion of transparent spacer layers enables enhancement of CD intensity by optimizing the optical pitch, which is experimentally validated. These results establish a versatile platform for engineering chiroptical responses from achiral polymer systems through structurally defined helical architectures.