Fig. 1

Optical properties and microstructures of PffBT4T-2DT mono- to multilayers. a Chemical structure of PffBT4T-2DT. b UV–Vis absorption spectra of PffBT4T-2DT as thin films and in solution of chloroform (0.025 mg mL⁻¹, 25 °C). Thin films are deposited on quartz wafers by dip-coating from 0.5 mg mL⁻¹ chloroform solution at room temperature. c AFM images of PffBT4T-2DT ultrathin films from multilayers down to monolayer obtained at different dip-coating speeds (50, 100, 200, 400, and 1000 μm s⁻¹) from 0.5 mg mL⁻¹ chloroform solution. All AFM images have the same scale x, y, and z bars except the height scale of the tetralayer. d The corresponding height profiles along the indicated lines in c