Figure 7: ¹(TT) decay through activated triplet hopping.

(a) Kinetics of ¹(TT) and free triplet species in F₂-TES ADT films, extracted from TA measurements over the temperature range 4–250 K and revealing temperature-dependent conversion. Kinetics presented on separate time axes for clarity. (b) Rate of ¹(TT) decay as a function of temperature. Error bars are uncertainty in the exponential fitting of ¹(TT) decay. Dashed lines are mono-exponential fits to the high-temperature data. Although the overall rate of ¹(TT) separation varies widely, the temperature dependence is strikingly similar across the series (activation energy ∼20–40 meV). Data for pentacene-based materials scaled by 0.1 × for clarity. (c) Marcus–Levich–Jortner rate model of ¹(TT) separation for three π-stacked systems. The strong variation in rate is attributed to the triplet-transfer coupling, while the temperature dependence is primarily governed by the enthalpy of ¹(TT) separation. (d) Normalized population kinetics of excited-state species extracted from TA measurements (solid) and PL measurements (dashed) of F₂-ADT single crystal at 200 and 110 K (see also Supplementary Fig. 21). As in thin films, sequential conversion from S₁ to emissive ¹(TT) to free triplets is observed, but ¹(TT) separation is fully suppressed at low temperature. (e) Normalized, temperature-dependent decay kinetics of ¹(TT) in F₂-ADT single crystal. At low temperature where no free triplets are formed, the decay converges to the intrinsic ¹(TT) lifetime.