Fig. 3: Triplet-pair-state population and SF mechanisms.
From: Vacancy control in acene blends links exothermic singlet fission to coherence
a Calculated dynamics of the triplet-pair- (TT) state population for PEN and TET. The numbers indicate the average number of nearest neighbours (NN) and the corresponding PEN or TET fraction in the blend. b Top panel: TT admixture into the photoexcited singlet state. Bottom panel: Reproduction of the calculated SF rates (unscaled) from Figs. 2c, d (filled circles), shown alongside rescaled values of the TT admixture (open symbols, solid lines) and the number of nearest neighbours (dashed lines). Correlations between the SF rates and these values are indicative of the relative coherent and incoherent contributions to the dynamics, respectively. All values for zero nearest neighbours vanish for trivial reasons, see main text, and are not shown here. c Schematic of the two pathways of SF in PEN and TET. Due to the endothermicity of SF in TET, the triplet-pair states cannot coherently mix into the photoexcited singlet state, in contrast to PEN where such mixing is mediated by a vibrational quantum (denoted by the *).
