Figure 5: ¹(TT) absorption in F₂-TES ADT.

(a) TA spectra of F₂-TES ADT films at 300 K, averaged over the indicated delay ranges. The initial singlet state (peaks 750–800 nm and >1,100 nm) converts directly into triplet excitons (peak centred at 970 nm) over ∼300 ps, through singlet fission. (b) TA spectra of F₂-TES ADT dilute solution (top, 0.08 mM), concentrated solution (middle, 32 mM) and thin film measured at 50 K (bottom). Extracted spectra (thick lines) closely follow the raw data at different time delays, revealing the presence of substantial triplet population (T₁+T₁) in concentrated solutions and thin film, as well as a distinct intermediate state ¹(TT). Extracted spectra of the three species in the film at 50 K are normalized in the bottom panel for clarity. (c) Normalized population kinetics of excited state species extracted from TA maps, exhibiting a sequential progression: singlet (black), ¹(TT) (red) and free triplets (purple). Also plotted are the integrated NIR TA signal (brown, diamonds) and kinetics extracted from the separate transient PL experiment (dashed lines). The agreement of PL and TA population kinetics confirms the same species are observed in both experiments.