Triplet Energy Transfer Governs the Dissociation of the Correlated Triplet Pair in Exothermic Singlet Fission

Abstract

Singlet fission is a spin-allowed process of exciton multiplication that has the potential to enhance the efficiency of photovoltaic devices. The majority of studies to date have emphasized understanding the first step of singlet fission, where the correlated triplet pair is produced. Here, we examine separation of correlated triplet pairs. We conducted temperature-dependent transient absorption on 6,3-bis(tri isopropylsilylethynyl)pentacene (TIPS-Pn) films, where singlet fission is exothermic. We evaluated time constants to show that their temperature dependence is inconsistent with an exclusively thermally activated process. Instead, we found that the trends can be modeled by a triplet-triplet energy transfer. The fitted reorganization energy and electronic coupling agree closely with values calculated using density matrix renormalization group quantum-chemical theory. We conclude that dissociation of the correlated triplet pair to separated (but spin-entangled) triplet excitons in TIPS-Pn occurs by triplet-triplet energy transfer with a hopping time constant of approximately 3.5 ps at room temperature.

Multiexcitonic Triplet Pair Generation in Oligoacene Dendrimers as Amorphous Solid‐State Miniatures

“…Recently, Lee et al. reported biexponential SF dynamics in polycrystalline films of TIPS‐pentacene employing temperature‐dependent transient absorption measurements [64] . The second process followed by multiexcitonic triplet pair generation was described as a triplet energy transfer process, which develops loosely bound triplet pair.…”

Activating intramolecular singlet exciton fission by altering π-bridge flexibility in perylene diimide trimers for organic solar cells

“…(ii) A fast triplet formation ($340 ps) observed via femtosecond transient absorption measurements. (iii) Distinct triplet species detected via transient absorption experiments -the correlated triplet pair and the independent triplets with lifetime of 6 ms. [64][65][66] (iv) A decay lifetime different from that of the S 1 species (4.7 ns), attributed to the double triplet species. (v) Thermodynamic viability -E(S 1 ) $ 2 Â E(T 1 ).…”

Highly Efficient One-Dimensional Triplet Exciton Transport in a Palladium–Porphyrin-Based Surface-Anchored Metal–Organic Framework

“…Although this value is significantly higher than TEET rates in (disordered) conjugated polymers (10 6 s -1 ), 41 it is similar to TEET rates in tetracyanoquinodimethane (TCNQ) salts (10 7 s -1 -10 11 s -1 ), 42 tetracene crystals (10 10 s -1 -10 11 s -1 ), 43 or triisopropylsilylethynyl acetylene (TIPS) pentacene thin films (10 11 s -1 ). 44 In the realm of MOFs, the 1D TEET rate in a Ru-trisbipyridyl-based system (with chromophore separation distances of >0.8 nm) was reported to be on the order of 10 8 s -1 . 27 Förster transport of singlet excitons was found to be faster in two different Zn-porphyrin MOFs (10 12 s -1 -10 13 s -1 ), 17,21 whereas our hoping rate is similar to the electron transfer rate in a pyrene based MOF (10 10 s -1 ).…”