Figure 5.

TrCD spectroscopy with Pump Modulation (TrCDwPM) for chiral F8BT:( +)-2 and F8BT:( −)-2 thin film blends annealed at 220 °C as well as an achiral F8BT thin film. (a) Illustration of the TrCD experiment with polarisation modulation of the pump beam: LCP pump beam (top) and RCP pump beam (middle) providing access to an experiment with randomly polarised excitation (bottom) due to the noncoherent nature of the two pump processes. In each case, the photoinduced dynamics is alternately detected by LCP and RCP supercontinuum probe pulses. (b) Corresponding transient absorption spectra of F8BT:( +)-2 (left column) and F8BT:( −)-2 (right column) for excitation with an LCP pump beam (top row) or an RCP pump beam (middle row) providing the pump-polarisation-averaged spectra (bottom row). Transient absorption spectra for an LCP probe beam (ΔOD_L, green solid lines) and an RCP probe beam (ΔOD_R, red solid lines) are shown in each case. (c) Resulting TrCD spectra (ΔOD_L − ΔOD_R) for LCP excitation (TrCD_L, top), for RCP excitation (TrCD_R, middle) and the pump-polarisation-averaged spectra (TrCD_avg = (TrCD_L + TrCD_R)/2). Results for F8BT:( +)-2 (blue solid lines) and F8BT:( −)-2 (violet solid lines) thin films as well as an achiral F8BT thin film without chiral additive (orange solid lines) are shown. In all cases, the samples were excited at 400 nm, and 21 spectra in the time-delay range 1–3 ps were averaged.