Geminate and Nongeminate Recombination of Triplet Excitons Formed by Singlet Fission

Bayliss, Sam L.; Chepelianskii, A. D.; Sepe, Alessandro; Walker, Brian; Ehrler, Bruno; Bruzek, Matthew J.; Anthony, John E.; Greenham, Neil C.

doi:10.1103/physrevlett.112.238701

Cited by 78 publications

(111 citation statements)

References 46 publications

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“…4 displays representative molecular and crystal lengthscales for comparison), consistent with the weak intermolecular coupling suggested by the TIPS-tetracene crystal packing [ Fig. 4(a)], 38 and other estimates of triplet localization in organic semiconductors.…”

Section: Experimental Methodsmentioning

confidence: 65%

Localization length scales of triplet excitons in singlet fission materials

et al. 2015

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We measure the dielectric confinement lengthscales of triplet excitons in organic semiconductors by jointly measuring their microwave-domain electric and magnetic susceptibilities. We apply this technique to characterize triplet excitons in two singlet fission materials with distinct solid-state packing, and correlate the extracted localization lengthscales with the role of the excitonic environment. Using the magnetic susceptibility simultaneously determined through our experiments, we compare the independently extracted dielectric and spin-spin localization lengthscales, highlighting the role of local anisotropy on the properties of excitonic triplet states.

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Section: Experimental Methodsmentioning

confidence: 65%

Localization length scales of triplet excitons in singlet fission materials

et al. 2015

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“…The results in Figure 3 thus show complete depopulation of S 1 and conversion into T 1 within 2 ps following photoexcitation, a time scale too fast for intersystem crossing in the absence of heavy atoms. It follows that DP-Mes exhibits rapid intramolecular SEF, presumably resulting in one triplet exciton strongly localized on each pentacene unit, [ 20 ] and since we detect no competing decay channels it is likely to be highly effi cient.…”

Section: Intramolecular Sefmentioning

confidence: 99%

“…This value is unexpectedly high and reveals a signifi cant perturbation of the pentacene energetic landscape upon dimerization, resulting in a strong reduction of the driving force for SEF relative to pentacene and its derivatives. [ 20 ] …”

Section: Triplet Generation and Annihilation Under Geometric Constraintmentioning

confidence: 99%

Tuneable Singlet Exciton Fission and Triplet–Triplet Annihilation in an Orthogonal Pentacene Dimer

Lukman

Musser

Chen

et al. 2015

Adv Funct Materials

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5452 wileyonlinelibrary.com proceed on ultrafast (≈100 fs) time scales, allowing it to out-compete other decay channels and achieve high effi ciencies. [ 3 ] The essential condition for effi cient SEF is the energetic alignment of the singlet and triplet states, such that 2 E (T 1 ) ≤ E (S 1 ). A recent combined theoretical and experimental study of SEF rates in a range of acene solids has demonstrated that the rate of SEF is also greatly affected by the strength of intermolecular coupling within the fi lm. [ 4 ] In the canonical system, pentacene, triplet pair formation is exothermic and the intermolecular coupling is strong, resulting in SEF with an 80 fs time constant and nearly 200% yield. [ 5 ] Though most experimental studies of SEF have involved crystalline, polycrystalline or amorphous solids, the most basic unit capable of SEF is a pair of chromophores. Indeed, it was recently demonstrated in concentrated solutions of TIPS-pentacene that singlet fi ssion can proceed at high efficiency through bimolecular diffusional interactions. [ 6 ] However, early attempts to directly control the interaction between chromophores through the use of covalent dimers have not been as successful. The most notable systems in this regard are tetracene and 1,3-diphenylisobenzofuran. These materials are found to exhibit effi cient SEF in the solid state, but their covalent dimers achieved triplet yields of only a few percent. In both of these studies, [ 7 ] the two SEF chromophores were joined by a range of linkers to modify the strength of the electronic coupling between them, with the aim of tuning the rate and effi ciency of SEF. The impact was subtle, and it thus remains unclear why covalent dimers have proved ineffi cient to date. Current models suggest that dimers should be asymmetric or contain signifi cant cofacial interaction between chromophores to attain high triplet yields. [ 2,8 ] Interestingly, a recent study of pentacene dimers separated by a phenyl spacer unit achieved triplet yields above 100% in spite of using the same symmetric bonding motifs of the earlier tetracene dimers. [ 9 ] In this work, we report highly effi cient intramolecular SEF in a new type of covalent dimer, with triplet yields of up to 192 ± 3%. The molecule used in this study, 13,13′-bis(mesityl)-6,6′-dipentacenyl (DP-Mes, Figure 1 a), consists of two pentacenes directly bonded through a single C C bond with two bulky mesityl groups at the meso -positions. The geometry of the dimer, with two nearly orthogonal pentacene cores, is unlike Tuneable Singlet Exciton Fission and Triplet-Triplet Annihilation in an Orthogonal Pentacene DimerSteven Lukman , Andrew J. Musser , Kai Chen , Stavros Athanasopoulos , Chaw K. Yong , Zebing Zeng , Qun Ye , Chunyan Chi , Justin M. Hodgkiss , Jishan Wu , * Richard H. Friend , and Neil C. Greenham * Fast and highly effi cient intramolecular singlet exciton fi ssion in a pentacene dimer, consisting of two covalently attached, nearly orthogonal pentacene units is reported. Fission to triplet excitons from...

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“…In light of both aspects, hydrocarbons such as acenes--tetracene, pentacene, hexacene--and their derivatives are at the forefront of investigations toward a sound understanding and development of molecular building blocks for SF. In tetracenes, the singlet-and triplet-pair energy levels are nearly degenerate (S 1 = 2T 1 ), leaving no or little standard enthalpy of reaction for SF (12). In solution, the latter is, however, offset by sizable entropy rendering the process rather slow and, thus, inefficient (13).…”

mentioning

confidence: 99%

Singlet fission in pentacene dimers

Zirzlmeier

Lehnherr

Coto

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

389

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Singlet fission (SF) has the potential to supersede the traditional solar energy conversion scheme by means of boosting the photonto-current conversion efficiencies beyond the 30% ShockleyQueisser limit. Here, we show unambiguous and compelling evidence for unprecedented intramolecular SF within regioisomeric pentacene dimers in room-temperature solutions, with observed triplet quantum yields reaching as high as 156 ± 5%. Whereas previous studies have shown that the collision of a photoexcited chromophore with a ground-state chromophore can give rise to SF, here we demonstrate that the proximity and sufficient coupling through bond or space in pentacene dimers is enough to induce intramolecular SF where two triplets are generated on one molecule.acene oligomers | excited states | singlet fission | multireference perturbation theory | time-resolved spectroscopy S inglet fission (SF) is a spin-allowed process to convert one singlet excited state into two triplet excited states, namely a correlated triplet pair (1). The ability to effectively implement SF processes in solar cells could allow for more efficient harvesting of high-energy photons from the solar spectrum and allow for the design of solar cells to circumvent the Shockley-Queisser performance limit (2). Indeed, several recent studies have demonstrated remarkably efficient solar cell devices based on SF (3-6).One requirement that needs to be met to achieve SF is that the photoexcited chromophore in its singlet excited state must share its energy with a neighboring ground-state chromophore. As such, the potential of coupled chromophores to afford two triplet excited states via SF has been elucidated in, for example, a tetracene dimer with an SF yield of around 3% (3, 7). Additionally, past experiments in single-crystal, polycrystalline, and amorphous solids of pentacene have documented that the efficiency of SF relates to the electronic coupling between these two chromophores (8, 9). Hence, molecular ordering in terms of crystal packing, that is, proximity, distances, orbital overlap, etc., is decisive with respect to gaining full control over and to finetuning interchromophoric interactions in the solid state (10, 11). Of equal importance are the thermodynamic requirements, namely that the energy of the lowest-lying singlet absorbing state must match or exceed the energy of two triplet excited states (S 1 ≥ 2T 1 ) (11). In light of both aspects, hydrocarbons such as acenes--tetracene, pentacene, hexacene--and their derivatives are at the forefront of investigations toward a sound understanding and development of molecular building blocks for SF. In tetracenes, the singlet-and triplet-pair energy levels are nearly degenerate (S 1 = 2T 1 ), leaving no or little standard enthalpy of reaction for SF (12). In solution, the latter is, however, offset by sizable entropy rendering the process rather slow and, thus, inefficient (13). In addition, the low SF yield relates to the dimer geometry. Its nature hinders electronic coupling through space, leaving only thro...

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Geminate and Nongeminate Recombination of Triplet Excitons Formed by Singlet Fission

Cited by 78 publications

References 46 publications

Localization length scales of triplet excitons in singlet fission materials

Localization length scales of triplet excitons in singlet fission materials

Tuneable Singlet Exciton Fission and Triplet–Triplet Annihilation in an Orthogonal Pentacene Dimer

Singlet fission in pentacene dimers

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