Singlet Exciton Fission in Polycrystalline Thin Films of a Slip-Stacked Perylenediimide

Eaton, Samuel W.; Shoer, Leah E.; Karlen, Steven D.; Dyar, Scott M.; Margulies, Eric A.; Veldkamp, Brad S.; Ramanan, Charusheela; Hartzler, Daniel A.; Savikhin, Sergei; Marks, Tobin J.; Wasielewski, Michael R.

doi:10.1021/ja4053174

Cited by 321 publications

(501 citation statements)

References 157 publications

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“…Accordingly, also in these cases other relaxation pathways prevail which could be, among other possibilities, via charge-transfer states or singlet fission to give two triplet states. The latter process has recently been discovered by Wasielewski and co-workers for slipped-stack PBI solid state materials [277] and rationalized by theoretical studies, which consider slipped stack arrangements as a requirement for the singlet fission process. [278] Albeit on first glance similar molecules, core-twisted tetraphenoxy-substituted PBIs 5, 6 (Figure 19b) are known to direct different packing arrangements than their planar congeners 3 and 4 due to the twisted cores of the former PBIs and their existence as M-and P-atropoisomers.…”

Section: Supramolecular Systems: Perylene Bisimide H-and J-aggregatesmentioning

confidence: 78%

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

Brixner

Hildner

Köhler

et al. 2017

Advanced Energy Materials

284

299

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The transport of excitation energy in molecular aggregates is of crucial importance for the function of organic optoelectronic devices and next‐generation solar cells. First, this review summarizes the theoretical background of the nature of the electronically excited states of molecular aggregates. For these systems, the electronic interaction between the monomers leads to the formation of exciton states. This goes along with a shift of the excitation energies and a redistribution of the oscillator strength with respect to the monomers. Next, a brief overview is provided over experimental techniques that allow to study the properties of excitons in molecular aggregates. This includes single‐molecule spectroscopy, coherent two‐dimensional (2D) spectroscopy, and single‐molecule coherent spectroscopy. Finally, examples of molecular aggregates spanning the range from natural systems that act in photosynthesis as light‐harvesting antennas to artificial aggregates built from synthetic chromophores are illustrated.

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Section: Supramolecular Systems: Perylene Bisimide H-and J-aggregatesmentioning

confidence: 78%

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

Brixner

Hildner

Köhler

et al. 2017

Advanced Energy Materials

284

299

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“…[3][4][5][6][7] On the other hand it has been recently found that excimer formation can also have a positive effect on the properties of organic materials, facilitating processes such as singlet fission. [8][9][10][11][12] For this reason, the understanding of the excimer formation dynamics in molecular aggregates is of fundamental importance for the development of novel materials that can be employed in organic electronics or photovoltaics applications. In addition to their importance for the development of functional materials, excimers can be also employed as probes in biological molecules.…”

Section: Introductionmentioning

confidence: 99%

The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer

Hoche

Schmitt

Humeniuk

et al. 2017

Phys. Chem. Chem. Phys.

125

122

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a These authors contributed equally to the work. AbstractThe understanding of excimer formation in organic materials is of fundamental importance, since it profoundly influences their functional performance in applications such as light-harvesting, photovoltaics or organic electronics. We present a joint experimental and theoretical study of the ultrafast dynamics of excimer formation in the pyrene dimer, which is the archetype of an excimer forming system. We perform simulations of the nonadiabatic photodynamics in the frame of TDDFT that reveal two distinct excimer formation pathways in the gas-phase dimer. The first pathway involves local excited state relaxation close to the initial Frank-Condon geometry that is characterized by a strong excitation of the stacking coordinate exhibiting damped oscillations with a period of 350 fs that persist for at least 5 ps. The second excimer forming pathway involves large amplitude oscillations along the parallel shift 1 coordinate with a period of ≈ 900 fs that after intramolecular vibrational energy redistribution on a 2 ps time scale leads to the formation of a perfectly stacked dimer.The electronic relaxation within the excitonic manifold is mediated by the presence of conical intersections formed between fully delocalized excitonic states. Such conical intersections may generally arise in stacked π-conjugated aggregates due to the interplay between the long-range and short-range electronic coupling. The simulations are supported by picosecond photoionization experiments in a supersonic jet that provide a time-constant for the excimer formation of around 6-8 ps, in excellent agreement with theory. Finally, in order to explore how the crystal environment influences the excimer formation dynamics we perform large scale QM/MM nonadiabatic dynamics simulations on a pyrene crystal in the framework of the tight-binding TDDFT. In contrast to the isolated dimer, the excimer formation in the crystal follows a single reaction pathway in which the initially excited parallel slip motion is strongly damped by collisions with the surrounding molecules leading to the slow excimer stabilization with a time constant of several picoseconds.2

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“…suggests a viable strategy. If successful, two charge carriers might be produced per absorbed photon and the photocurrents of the device can reach external quantum efficiencies of more than 100% (5,17,18).A provocative debate has been ignited about the mechanism of SF at the molecular level (19,20). Controversy exists around the electronic states that are involved in the process, the coupling among them, and the effective nuclear dynamics (14,(21)(22)(23)(24)(25)(26)(27).…”

mentioning

confidence: 99%

mentioning

confidence: 99%

Singlet fission in pentacene dimers

Zirzlmeier

Lehnherr

Coto

et al. 2015

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

387

646

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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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Singlet Exciton Fission in Polycrystalline Thin Films of a Slip-Stacked Perylenediimide

Cited by 321 publications

References 157 publications

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer

Singlet fission in pentacene dimers

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