Fig. 2. (a) Absorption spectra of TPA-PTZ-BDP, PTZ-TPA-BDP and N-PTZ-BDP recorded in DCM solution (1 × 10⁻⁵ M) and in (b) thin film form. (c) Normalised time-integrated fluorescence spectra of BODIPY derivatives (d) decay kinetics of the neat films recorded after excitation at 515 nm for PC₇₁BM and at 660 nm for BODIPY derivatives. Kinetics were obtained by integrating fluorescence spectra over a 150 nm window for BODIPY derivatives and a 200 nm window for PC₇₁BM. Because of the weak fluorescence emission of BODIPY derivatives, the plots shown in (c) are smoothed for clarity of spectral shape.