Singlet exciton fission via an intermolecular charge transfer state in coevaporated pentacene-perfluoropentacene thin films

Kim, Vincent; Broch, Katharina; Belova, Valentina; Chen, Y. S.; Gerlach, Alexander; Schreiber, Frank; Tamura, Hiroyuki; Valle, Raffaele Guido Della; D’Avino, Gabriele; Salzmann, Ingo; Beljonne, David; Rao, Akshay; Friend, Richard H.

doi:10.1063/1.5130400

Cited by 26 publications

(36 citation statements)

References 40 publications

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“…This is best reflected in the large number of studies that have explored the structural, optical, and electronic characteristics of such systems both experimentally and at various levels of theory during the last decade. 1,[3][4][5][6][7][8][9][10] The deep interest in these systems is rooted in the unique opportunities that halogenation offers for tuning excitonic and charge-transport energy levels over a wide range. The functionalization of the ⇡-conjugated molecular cores with fluorine permits tuning the electronic properties through the inductive effect exerted by these electron-withdrawing substituents 11,12 and via long-range electrostatic interactions in the solid state.…”

Section: Introductionmentioning

confidence: 99%

Electrostatic Interactions Shape Molecular Organization and Electronic Structure of Organic Semiconductor Blends

et al. 2020

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Halogenation of conjugated molecules represents a powerful approach to tune the electronic structure of molecular thin-films through inductive effects and long-range intermolecular electrostatic interactions. The mixing of halogenated molecules with their pristine counterparts has recently proven successful in altering the blend's energy levels to adjust the open-circuit voltage of organic solar cells by the mixing ratio. Here, we show that the prevailing rationale for this effect is not equally valid for different molecular orientations. We provide a comprehensive experimental and theoretical analysis of the prototypical blend formed by pentacene and perfluoropentacene to relate structure with electronic properties. We find a mixed-stack structural motif in standing and lying orientation depending on the substrate nature. In standing orientation, the ionization potential lies in between the values of the pure components, in line with the established picture of averaged molecular quadrupole moments. For the lying orientation, however, we experimentally observe an ionization potential lower than both pristine values, which seems at odds with this simple rationale. Electrostatic simulations based on the knowledge of the atomistic structure of the films capture the complex experimental scenario for both orientations. In particular, the ultra-low ionization potential of films formed by lying molecules is identified as a signature of the monolayer structure, where quadrupolar interactions are responsible for a difference of ca. 0.4 eV in the highest occupied molecular orbital energy as compared to thicker films with the same molecular orientation.

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Section: Introductionmentioning

confidence: 99%

Electrostatic Interactions Shape Molecular Organization and Electronic Structure of Organic Semiconductor Blends

et al. 2020

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“…The fact that 1 (TT) is observed as comparably long‐lived species in 12 might be due to the lower long‐range order in the thin film compared with 11 , reducing the delocalization of the 1 (TT) and increasing the dephasing time. Importantly, in both compounds 11 and 12 , SF proceeds faster than in pentacene and, surprisingly also in PFP . This cannot be explained by energetics, because SF in 11 and 12 is less exothermic than in pentacene and, therefore, might be related to differences in the relative molecular arrangement.…”

Section: Resultsmentioning

confidence: 99%

“…Importantly,i nb oth compounds 11 and 12,S Fp roceeds faster than in pentacene and, surprisingly also in PFP. [63,73] This cannot be explained by energetics, because SF in 11 and 12 is less exothermict han in pentacene and, therefore, might be relatedt o differences in the relative molecular arrangement.…”

Section: Transient-absorption Spectroscopy Of Thin Films Of Tetrafluomentioning

confidence: 99%

Modulating the Electronic and Solid‐State Structure of Organic Semiconductors by Site‐Specific Substitution: The Case of Tetrafluoropentacenes

Geiger

Schundelmeier

Hummel

et al. 2020

Chemistry A European J

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The properties as well as solid‐state structures, singlet fission, and organic field‐effect transistor (OFET) performance of three tetrafluoropentacenes (1,4,8,11: 10, 1,4,9,10: 11, 2,3,9,10: 12) are compared herein. The novel compounds 10 and 11 were synthesized in high purity from the corresponding 6,13‐etheno‐bridged precursors by reaction with dimethyl 1,2,4,5‐tetrazine‐3,6‐dicarboxylate at elevated temperatures. Although most of the molecular properties of the compounds are similar, their chemical reactivity and crystal structures differ considerably. Isomer 10 undergoes the orbital symmetry forbidden thermal [4+4] dimerization, whereas 11 and 12 are much less reactive. The isomers 11 and 12 crystallize in a herringbone motif, but 10 prefers π–π stacking. Although the energy of the first electric dipole‐allowed optical transition varies only within 370 cm−1 (0.05 eV) for the neutral compounds, this amounts to roughly 1600 cm−1 (0.20 eV) for radical cations and 1300 cm−1 (0.16 eV) for dications. Transient spectroscopy of films of 11 and 12 reveals singlet‐fission time constants (91±11, 73±3 fs, respectively) that are shorter than for pentacene (112±9 fs). OFET devices constructed from 11 and 12 show close to ideal thin‐film transistor (TFT) characteristics with electron mobilities of 2×10−3 and 6×10−2 cm2 V−1 s−1, respectively.

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“…Theaim of our study is to continue this promising route by taking advantage of intermolecular heterofission in blends of SF chromophores. [16][17][18] We focus in particular on the prototypical SF chromophores pentacene (PEN) and tetracene (TET), whose structures are shown in Figure 1a.T hese two materials have been shown early on to efficiently undergo intermolecular SF (xSF) in neat thin films and single crystals [19,20] and iSF in dimers and polymers. [9,12,13,15] While SF in TET is endothermic and occurs with atime constant of 80-90 ps, [21,22] in PEN it is exothermic with an ultrafast time constant of 80 fs.…”

Section: Introductionmentioning

confidence: 99%

“…The aim of our study is to continue this promising route by taking advantage of intermolecular heterofission in blends of SF chromophores [16–18] . We focus in particular on the prototypical SF chromophores pentacene (PEN) and tetracene (TET), whose structures are shown in Figure 1 a.…”

Section: Introductionmentioning

confidence: 99%

Singlet Heterofission in Tetracene–Pentacene Thin‐Film Blends

et al. 2020

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Heterofission is a photophysical process of fundamental and applied interest whereby an excited singlet state is converted into two triplets on chemically distinct chromophores. The potential of this process lies in the tuning of both the optical band gap and the splitting between singlet and triplet energies. Herein, we report the time‐domain observation of heterofission in mixed thin films of the prototypical singlet fission chromophores pentacene and tetracene using excitation wavelengths above and below the tetracene band gap. We found a time constant of 26 ps for endothermic heterofission of a singlet exciton on pentacene in blends with low pentacene fractions, which was outcompeted by pentacene homofission for increasing pentacene concentrations. Direct excitation of tetracene lead to fast energy transfer to pentacene and subsequent singlet fission, which prevented homo‐ or heterofission of a singlet exciton on tetracene.

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Singlet exciton fission via an intermolecular charge transfer state in coevaporated pentacene-perfluoropentacene thin films

Abstract: Paper published as part of the special topic on Singlet Fission Note: This paper is part of the JCP Special Collection on Singlet Fission.

Cited by 26 publications

References 40 publications

Electrostatic Interactions Shape Molecular Organization and Electronic Structure of Organic Semiconductor Blends

Electrostatic Interactions Shape Molecular Organization and Electronic Structure of Organic Semiconductor Blends

Modulating the Electronic and Solid‐State Structure of Organic Semiconductors by Site‐Specific Substitution: The Case of Tetrafluoropentacenes

Singlet Heterofission in Tetracene–Pentacene Thin‐Film Blends

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