repeating units. This localization of the excited-state wavefunction, i.e., the shorter conjugation length after geometric relaxation in the excited state, is likely induced by more strongly distorted conformations in the relaxed excited state, which also results in neither S1 nor T1 showing an appreciable red-shift along the series (Table ). The larger kRISC cannot be due to the difference in DEST because the measured activation energy for TADF is the same for all three compounds (c.f. Figure ).