1
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Zhang Q, Shao X, Li W, Mi W, Pavanello M, Akimov AV. Nonadiabatic molecular dynamics with subsystem density functional theory: application to crystalline pentacene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:385901. [PMID: 38866023 DOI: 10.1088/1361-648x/ad577d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2024] [Accepted: 06/12/2024] [Indexed: 06/14/2024]
Abstract
In this work, we report the development and assessment of the nonadiabatic molecular dynamics approach with the electronic structure calculations based on the linearly scaling subsystem density functional method. The approach is implemented in an open-source embedded Quantum Espresso/Libra software specially designed for nonadiabatic dynamics simulations in extended systems. As proof of the applicability of this method to large condensed-matter systems, we examine the dynamics of nonradiative relaxation of excess excitation energy in pentacene crystals with the simulation supercells containing more than 600 atoms. We find that increased structural disorder observed in larger supercell models induces larger nonadiabatic couplings of electronic states and accelerates the relaxation dynamics of excited states. We conduct a comparative analysis of several quantum-classical trajectory surface hopping schemes, including two new methods proposed in this work (revised decoherence-induced surface hopping and instantaneous decoherence at frustrated hops). Most of the tested schemes suggest fast energy relaxation occurring with the timescales in the 0.7-2.0 ps range, but they significantly overestimate the ground state recovery rates. Only the modified simplified decay of mixing approach yields a notably slower relaxation timescales of 8-14 ps, with a significantly inhibited ground state recovery.
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Affiliation(s)
- Qingxin Zhang
- Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, NY 14260, United States of America
| | - Xuecheng Shao
- Department of Physics, Rutgers University, The State University of New Jersey, Newark, NJ 07102, United States of America
| | - Wei Li
- School of Chemistry and Materials Science, Hunan Agricultural University, Changsha 410128, People's Republic of China
| | - Wenhui Mi
- Key Laboratory of Material Simulation Methods & Software of Ministry of Education, College of Physics, Jilin University, Changchun 130012, People's Republic of China
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People's Republic of China
| | - Michele Pavanello
- Department of Physics, Rutgers University, The State University of New Jersey, Newark, NJ 07102, United States of America
| | - Alexey V Akimov
- Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, NY 14260, United States of America
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2
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Cohen G, Haber JB, Neaton JB, Qiu DY, Refaely-Abramson S. Phonon-Driven Femtosecond Dynamics of Excitons in Crystalline Pentacene from First Principles. PHYSICAL REVIEW LETTERS 2024; 132:126902. [PMID: 38579218 DOI: 10.1103/physrevlett.132.126902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2023] [Revised: 08/24/2023] [Accepted: 02/11/2024] [Indexed: 04/07/2024]
Abstract
Nonradiative exciton relaxation processes are critical for energy transduction and transport in optoelectronic materials, but how these processes are connected to the underlying crystal structure and the associated electron, exciton, and phonon band structures, as well as the interactions of all these particles, is challenging to understand. Here, we present a first-principles study of exciton-phonon relaxation pathways in pentacene, a paradigmatic molecular crystal and optoelectronic semiconductor. We compute the momentum- and band-resolved exciton-phonon interactions, and use them to analyze key scattering channels. We find that both exciton intraband scattering and interband scattering to parity-forbidden dark states occur on the same ∼100 fs timescale as a direct consequence of the longitudinal-transverse splitting of the bright exciton band. Consequently, exciton-phonon scattering exists as a dominant nonradiative relaxation channel in pentacene. We further show how the propagation of an exciton wave packet is connected with crystal anisotropy, which gives rise to the longitudinal-transverse exciton splitting and concomitant anisotropic exciton and phonon dispersions. Our results provide a framework for understanding the role of exciton-phonon interactions in exciton nonradiative lifetimes in molecular crystals and beyond.
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Affiliation(s)
- Galit Cohen
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Jonah B Haber
- Department of Physics, University of California Berkeley, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Jeffrey B Neaton
- Department of Physics, University of California Berkeley, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Kavli Energy Nanosciences Institute at Berkeley, Berkeley, California 94720, USA
| | - Diana Y Qiu
- Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06520, USA
| | - Sivan Refaely-Abramson
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
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3
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Unger F, Lepple D, Asbach M, Craciunescu L, Zeiser C, Kandolf AF, Fišer Z, Hagara J, Hagenlocher J, Hiller S, Haug S, Deutsch M, Grüninger P, Novák J, Bettinger HF, Broch K, Engels B, Schreiber F. Optical Absorption Properties in Pentacene/Tetracene Solid Solutions. J Phys Chem A 2024; 128:747-760. [PMID: 38232326 DOI: 10.1021/acs.jpca.3c06737] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2024]
Abstract
Modifying the optical and electronic properties of crystalline organic thin films is of great interest for improving the performance of modern organic semiconductor devices. Therein, the statistical mixing of molecules to form a solid solution provides an opportunity to fine-tune optical and electronic properties. Unfortunately, the diversity of intermolecular interactions renders mixed organic crystals highly complex, and a holistic picture is still lacking. Here, we report a study of the optical absorption properties in solid solutions of pentacene and tetracene, two prototypical organic semiconductors. In the mixtures, the optical properties can be continuously modified by statistical mixing at the molecular level. Comparison with time-dependent density functional theory calculations on occupationally disordered clusters unravels the electronic origin of the low energy optical transitions. The disorder partially relaxes the selection rules, leading to additional optical transitions that manifest as optical broadening. Furthermore, the contribution of diabatic charge-transfer states is modified in the mixtures, reducing the observed splitting in the 0-0 vibronic transition. Additional comparisons with other blended systems generalize our results and indicate that changes in the polarizability of the molecular environment in organic thin-film blends induce shifts in the absorption spectrum.
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Affiliation(s)
- Frederik Unger
- Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
| | - Daniel Lepple
- Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
| | - Maximilian Asbach
- Julius-Maximilian University Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Luca Craciunescu
- Julius-Maximilian University Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS Scotland, U.K
| | - Clemens Zeiser
- Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
| | - Andreas F Kandolf
- Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
- Institute of Organic Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Zbyněk Fišer
- Department of Condensed Matter Physics (UFKL), Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic
| | - Jakub Hagara
- Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
| | - Jan Hagenlocher
- Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
| | - Stefan Hiller
- Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
| | - Sara Haug
- Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
| | - Marian Deutsch
- Julius-Maximilian University Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Peter Grüninger
- Institute of Organic Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Jiří Novák
- Department of Condensed Matter Physics (UFKL), Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic
| | - Holger F Bettinger
- Institute of Organic Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Katharina Broch
- Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
| | - Bernd Engels
- Julius-Maximilian University Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Frank Schreiber
- Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
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4
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Bhat V, Callaway CP, Risko C. Computational Approaches for Organic Semiconductors: From Chemical and Physical Understanding to Predicting New Materials. Chem Rev 2023. [PMID: 37141497 DOI: 10.1021/acs.chemrev.2c00704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
While a complete understanding of organic semiconductor (OSC) design principles remains elusive, computational methods─ranging from techniques based in classical and quantum mechanics to more recent data-enabled models─can complement experimental observations and provide deep physicochemical insights into OSC structure-processing-property relationships, offering new capabilities for in silico OSC discovery and design. In this Review, we trace the evolution of these computational methods and their application to OSCs, beginning with early quantum-chemical methods to investigate resonance in benzene and building to recent machine-learning (ML) techniques and their application to ever more sophisticated OSC scientific and engineering challenges. Along the way, we highlight the limitations of the methods and how sophisticated physical and mathematical frameworks have been created to overcome those limitations. We illustrate applications of these methods to a range of specific challenges in OSCs derived from π-conjugated polymers and molecules, including predicting charge-carrier transport, modeling chain conformations and bulk morphology, estimating thermomechanical properties, and describing phonons and thermal transport, to name a few. Through these examples, we demonstrate how advances in computational methods accelerate the deployment of OSCsin wide-ranging technologies, such as organic photovoltaics (OPVs), organic light-emitting diodes (OLEDs), organic thermoelectrics, organic batteries, and organic (bio)sensors. We conclude by providing an outlook for the future development of computational techniques to discover and assess the properties of high-performing OSCs with greater accuracy.
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Affiliation(s)
- Vinayak Bhat
- Department of Chemistry & Center for Applied Energy Research, University of Kentucky, Lexington, Kentucky 40506-0055, United States
| | - Connor P Callaway
- Department of Chemistry & Center for Applied Energy Research, University of Kentucky, Lexington, Kentucky 40506-0055, United States
| | - Chad Risko
- Department of Chemistry & Center for Applied Energy Research, University of Kentucky, Lexington, Kentucky 40506-0055, United States
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5
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Alvertis AM, Haber JB, Engel EA, Sharifzadeh S, Neaton JB. Phonon-Induced Localization of Excitons in Molecular Crystals from First Principles. PHYSICAL REVIEW LETTERS 2023; 130:086401. [PMID: 36898125 DOI: 10.1103/physrevlett.130.086401] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Revised: 01/20/2023] [Accepted: 01/23/2023] [Indexed: 06/18/2023]
Abstract
The spatial extent of excitons in molecular systems underpins their photophysics and utility for optoelectronic applications. Phonons are reported to lead to both exciton localization and delocalization. However, a microscopic understanding of phonon-induced (de)localization is lacking, in particular, how localized states form, the role of specific vibrations, and the relative importance of quantum and thermal nuclear fluctuations. Here, we present a first-principles study of these phenomena in solid pentacene, a prototypical molecular crystal, capturing the formation of bound excitons, exciton-phonon coupling to all orders, and phonon anharmonicity, using density functional theory, the ab initio GW-Bethe-Salpeter equation approach, finite-difference, and path integral techniques. We find that for pentacene zero-point nuclear motion causes uniformly strong localization, with thermal motion providing additional localization only for Wannier-Mott-like excitons. Anharmonic effects drive temperature-dependent localization, and, while such effects prevent the emergence of highly delocalized excitons, we explore the conditions under which these might be realized.
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Affiliation(s)
- Antonios M Alvertis
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Physics, University of California Berkeley, Berkeley, 94720 California, USA
| | - Jonah B Haber
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Physics, University of California Berkeley, Berkeley, 94720 California, USA
| | - Edgar A Engel
- Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Sahar Sharifzadeh
- Division of Materials Science and Engineering, Boston University, Boston, 02215 Massachusetts, USA
- Department of Electrical and Computer Engineering, Boston University, Boston, 02215 Massachusetts, USA
| | - Jeffrey B Neaton
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Physics, University of California Berkeley, Berkeley, 94720 California, USA
- Kavli Energy NanoScience Institute at Berkeley, Berkeley, 94720 California, USA
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6
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Seiler H, Zahn D, Taylor VCA, Bodnarchuk MI, Windsor YW, Kovalenko MV, Ernstorfer R. Direct Observation of Ultrafast Lattice Distortions during Exciton-Polaron Formation in Lead Halide Perovskite Nanocrystals. ACS NANO 2023; 17:1979-1988. [PMID: 36651873 PMCID: PMC9933605 DOI: 10.1021/acsnano.2c06727] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Accepted: 01/10/2023] [Indexed: 05/31/2023]
Abstract
The microscopic origin of slow hot-carrier cooling in lead halide perovskites remains debated and has direct implications for applications. Slow hot-carrier cooling of several picoseconds has been attributed to either polaron formation or a hot-phonon bottleneck effect at high excited carrier densities (>1018 cm-3). These effects cannot be unambiguously disentangled with optical experiments alone. However, they can be distinguished by direct observations of ultrafast lattice dynamics, as these effects are expected to create qualitatively distinct fingerprints. To this end, we employ femtosecond electron diffraction and directly measure the sub-picosecond lattice dynamics of weakly confined CsPbBr3 nanocrystals following above-gap photoexcitation. While we do not observe signatures of a hot-phonon bottleneck lasting several picoseconds, the data reveal a light-induced structural distortion appearing on a time scale varying between 380 and 1200 fs depending on the excitation fluence. We attribute these dynamics to the effect of exciton-polarons on the lattice and the slower dynamics at high fluences to slower sub-picosecond hot-carrier cooling, which slows down the establishment of the exciton-polaron population. Further analysis and simulations show that the distortion is consistent with motions of the [PbBr3]- octahedral ionic cage, and closest agreement with the data is obtained for Pb-Br bond lengthening. Our work demonstrates how direct studies of lattice dynamics on the sub-picosecond time scale can discriminate between competing scenarios proposed in the literature to explain the origin of slow hot-carrier cooling in lead halide perovskites.
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Affiliation(s)
- Hélène Seiler
- Fritz
Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
- Physics
Department, Free University of Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Daniela Zahn
- Fritz
Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - Victoria C. A. Taylor
- Fritz
Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - Maryna I. Bodnarchuk
- Laboratory
for Thin Films and Photovoltaics, Swiss
Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
| | - Yoav William Windsor
- Fritz
Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
- Institut
für Optik und Atomare Physik, Technische
Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany
| | - Maksym V. Kovalenko
- Laboratory
for Thin Films and Photovoltaics, Swiss
Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
- Institute
of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Ralph Ernstorfer
- Fritz
Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
- Institut
für Optik und Atomare Physik, Technische
Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany
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7
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Hammer S, Linderl T, Tvingstedt K, Brütting W, Pflaum J. Spectroscopic analysis of vibrational coupling in multi-molecular excited states. MATERIALS HORIZONS 2023; 10:221-234. [PMID: 36367085 DOI: 10.1039/d2mh00829g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Multi-molecular excited states accompanied by intra- and inter-molecular geometric relaxation are commonly encountered in optical and electrooptical studies and applications of organic semiconductors as, for example, excimers or charge transfer states. Understanding the dynamics of these states is crucial to improve organic devices such as light emitting diodes and solar cells. Their full microscopic description, however, demands sophisticated tools such as ab initio quantum chemical calculations which come at the expense of high computational costs and are prone to errors by assumptions as well as iterative algorithmic procedures. Hence, the analysis of spectroscopic data is often conducted at a phenomenological level only. Here, we present a toolkit to analyze temperature dependent luminescence data and gain first insights into the relevant microscopic parameters of the molecular system at hand. By means of a Franck-Condon based approach considering a single effective inter-molecular vibrational mode and different potentials for the ground and excited state we are able to explain the luminescence spectra of such multi-molecular states. We demonstrate that by applying certain reasonable simplifications the luminescence of charge transfer states as well as excimers can be satisfactorily reproduced for temperatures ranging from cryogenics to above room temperature. We present a semi-classical and a quantum-mechanical description of our model and, for both cases, demonstrate its applicability by analyzing the temperature dependent luminescence of the amorphous donor-acceptor heterojunction tetraphenyldibenzoperiflanthene:C60 as well as polycrystalline zinc-phthalocyanine to reproduce the luminescence spectra and extract relevant system parameters such as the excimer binding energy.
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Affiliation(s)
- Sebastian Hammer
- Experimental Physics VI, Julius Maximilian University Würzburg, 97074 Würzburg, Germany.
| | - Theresa Linderl
- Institute of Physics, University of Augsburg, 86135 Augsburg, Germany
| | - Kristofer Tvingstedt
- Experimental Physics VI, Julius Maximilian University Würzburg, 97074 Würzburg, Germany.
| | - Wolfgang Brütting
- Institute of Physics, University of Augsburg, 86135 Augsburg, Germany
| | - Jens Pflaum
- Experimental Physics VI, Julius Maximilian University Würzburg, 97074 Würzburg, Germany.
- Bavarian Center for Applied Energy Research, 97074 Würzburg, Germany
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8
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Boeije Y, Olivucci M. From a one-mode to a multi-mode understanding of conical intersection mediated ultrafast organic photochemical reactions. Chem Soc Rev 2023; 52:2643-2687. [PMID: 36970950 DOI: 10.1039/d2cs00719c] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/29/2023]
Abstract
This review discusses how ultrafast organic photochemical reactions are controlled by conical intersections, highlighting that decay to the ground-state at multiple points of the intersection space results in their multi-mode character.
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Affiliation(s)
- Yorrick Boeije
- Van 't Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Massimo Olivucci
- Chemistry Department, University of Siena, Via Aldo Moro n. 2, 53100 Siena, Italy
- Chemistry Department, Bowling Green State University, Overman Hall, Bowling Green, Ohio 43403, USA
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9
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Unger F, Moretti L, Hausch J, Bredehoeft J, Zeiser C, Haug S, Tempelaar R, Hestand NJ, Cerullo G, Broch K. Modulating Singlet Fission by Scanning through Vibronic Resonances in Pentacene-Based Blends. J Am Chem Soc 2022; 144:20610-20619. [DOI: 10.1021/jacs.2c07237] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Frederik Unger
- Institute for Applied Physics, University of Tuebingen, Auf der Morgenstelle 10, Tuebingen, 72076, Germany
| | - Luca Moretti
- Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, Milan 20133, Italy
| | - Julian Hausch
- Institute for Applied Physics, University of Tuebingen, Auf der Morgenstelle 10, Tuebingen, 72076, Germany
| | - Jona Bredehoeft
- Institute for Applied Physics, University of Tuebingen, Auf der Morgenstelle 10, Tuebingen, 72076, Germany
| | - Clemens Zeiser
- Institute for Applied Physics, University of Tuebingen, Auf der Morgenstelle 10, Tuebingen, 72076, Germany
| | - Sara Haug
- Institute for Applied Physics, University of Tuebingen, Auf der Morgenstelle 10, Tuebingen, 72076, Germany
| | - Roel Tempelaar
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
| | - Nicholas J. Hestand
- Department of Natural and Applied Sciences, Evangel University, 1111 North Glenstone Avenue, Springfield, Missouri 65802, United States
| | - Giulio Cerullo
- Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, Milan 20133, Italy
| | - Katharina Broch
- Institute for Applied Physics, University of Tuebingen, Auf der Morgenstelle 10, Tuebingen, 72076, Germany
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10
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Liu S, Hammud A, Hamada I, Wolf M, Müller M, Kumagai T. Nanoscale coherent phonon spectroscopy. SCIENCE ADVANCES 2022; 8:eabq5682. [PMID: 36269832 PMCID: PMC9586471 DOI: 10.1126/sciadv.abq5682] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2022] [Accepted: 09/02/2022] [Indexed: 06/02/2023]
Abstract
Coherent phonon spectroscopy can provide microscopic insight into ultrafast lattice dynamics and its coupling to other degrees of freedom under nonequilibrium conditions. Ultrafast optical spectroscopy is a well-established method to study coherent phonons, but the diffraction limit has hampered observing their local dynamics directly. Here, we demonstrate nanoscale coherent phonon spectroscopy using ultrafast laser-induced scanning tunneling microscopy in a plasmonic junction. Coherent phonons are locally excited in ultrathin zinc oxide films by the tightly confined plasmonic field and are probed via the photoinduced tunneling current through an electronic resonance of the zinc oxide film. Concurrently performed tip-enhanced Raman spectroscopy allows us to identify the involved phonon modes. In contrast to the Raman spectra, the phonon dynamics observed in coherent phonon spectroscopy exhibit strong nanoscale spatial variations that are correlated with the distribution of the electronic local density of states resolved by scanning tunneling spectroscopy.
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Affiliation(s)
- Shuyi Liu
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - Adnan Hammud
- Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - Ikutaro Hamada
- Department of Precision Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-Oka, Suita, Osaka 565-0871, Japan
| | - Martin Wolf
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - Melanie Müller
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - Takashi Kumagai
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
- Center for Mesoscopic Sciences, Institute for Molecular Science, Okazaki 444-8585, Japan
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11
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Ashoka A, Gauriot N, Girija AV, Sawhney N, Sneyd AJ, Watanabe K, Taniguchi T, Sung J, Schnedermann C, Rao A. Direct observation of ultrafast singlet exciton fission in three dimensions. Nat Commun 2022; 13:5963. [PMID: 36216826 PMCID: PMC9551063 DOI: 10.1038/s41467-022-33647-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Accepted: 09/26/2022] [Indexed: 11/06/2022] Open
Abstract
We present quantitative ultrafast interferometric pump-probe microscopy capable of tracking of photoexcitations with sub-10 nm spatial precision in three dimensions with 15 fs temporal resolution, through retrieval of the full transient photoinduced complex refractive index. We use this methodology to study the spatiotemporal dynamics of the quantum coherent photophysical process of ultrafast singlet exciton fission. Measurements on microcrystalline pentacene films grown on glass (SiO2) and boron nitride (hBN) reveal a 25 nm, 70 fs expansion of the joint-density-of-states along the crystal a,c-axes accompanied by a 6 nm, 115 fs change in the exciton density along the crystal b-axis. We propose that photogenerated singlet excitons expand along the direction of maximal orbital π-overlap in the crystal a,c-plane to form correlated triplet pairs, which subsequently electronically decouples into free triplets along the crystal b-axis due to molecular sliding motion of neighbouring pentacene molecules. Our methodology lays the foundation for the study of three dimensional transport on ultrafast timescales.
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Affiliation(s)
- Arjun Ashoka
- grid.5335.00000000121885934Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE UK
| | - Nicolas Gauriot
- grid.5335.00000000121885934Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE UK
| | - Aswathy V. Girija
- grid.5335.00000000121885934Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE UK
| | - Nipun Sawhney
- grid.5335.00000000121885934Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE UK
| | - Alexander J. Sneyd
- grid.5335.00000000121885934Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE UK
| | - Kenji Watanabe
- grid.21941.3f0000 0001 0789 6880Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044 Japan
| | - Takashi Taniguchi
- grid.21941.3f0000 0001 0789 6880International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044 Japan
| | - Jooyoung Sung
- grid.417736.00000 0004 0438 6721Department of Emerging Materials Science, DGIST, Daegu, 42988 Republic of Korea
| | - Christoph Schnedermann
- grid.5335.00000000121885934Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE UK
| | - Akshay Rao
- grid.5335.00000000121885934Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE UK
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12
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Sneyd A, Beljonne D, Rao A. A New Frontier in Exciton Transport: Transient Delocalization. J Phys Chem Lett 2022; 13:6820-6830. [PMID: 35857739 PMCID: PMC9340810 DOI: 10.1021/acs.jpclett.2c01133] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 07/18/2022] [Indexed: 05/20/2023]
Abstract
Efficient exciton transport is crucial to the application of organic semiconductors (OSCs) in light-harvesting devices. While the physics of exciton transport in highly disordered media is well-explored, the description of transport in structurally and energetically ordered OSCs is less established, despite such materials being favorable for devices. In this Perspective we describe and highlight recent research pointing toward a highly efficient exciton transport mechanism which occurs in ordered OSCs, transient delocalization. Here, exciton-phonon couplings play a critical role in allowing localized exciton states to temporarily access higher-energy delocalized states whereupon they move large distances. The mechanism shows great promise for facilitating long-range exciton transport and may allow for improved device efficiencies and new device architectures. However, many fundamental questions on transient delocalization remain to be answered. These questions and suggested next steps are summarized.
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Affiliation(s)
- Alexander
J. Sneyd
- Department
of Physics, Cavendish Laboratory, University
of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - David Beljonne
- Laboratory
for Chemistry of Novel Materials, University
of Mons, Mons 7000, Belgium
| | - Akshay Rao
- Department
of Physics, Cavendish Laboratory, University
of Cambridge, Cambridge CB3 0HE, United Kingdom
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13
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Asher M, Jouclas R, Bardini M, Diskin-Posner Y, Kahn N, Korobko R, Kennedy AR, Silva de Moraes L, Schweicher G, Liu J, Beljonne D, Geerts Y, Yaffe O. Chemical Modifications Suppress Anharmonic Effects in the Lattice Dynamics of Organic Semiconductors. ACS MATERIALS AU 2022; 2:699-708. [PMID: 36397874 PMCID: PMC9650719 DOI: 10.1021/acsmaterialsau.2c00020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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The lattice dynamics
of organic semiconductors has a significant
role in determining their electronic and mechanical properties. A
common technique to control these macroscopic properties is to chemically
modify the molecular structure. These modifications are known to change
the molecular packing, but their effect on the lattice dynamics is
relatively unexplored. Therefore, we investigate how chemical modifications
to a core [1]benzothieno[3,2-b]benzothiophene (BTBT)
semiconducting crystal affect the evolution of the crystal structural
dynamics with temperature. Our study combines temperature-dependent
polarization-orientation (PO) low-frequency Raman measurements with
first-principles calculations and single-crystal X-ray diffraction
measurements. We show that chemical modifications can indeed suppress
specific expressions of vibrational anharmonicity in the lattice dynamics.
Specifically, we detect in BTBT a gradual change in the PO Raman response
with temperature, indicating a unique anharmonic expression. This
anharmonic expression is suppressed in all examined chemically modified
crystals (ditBu-BTBT and diC8-BTBT, diPh-BTBT, and DNTT). In addition,
we observe solid–solid phase transitions in the alkyl-modified
BTBTs. Our findings indicate that π-conjugated chemical modifications
are the most effective in suppressing these anharmonic effects.
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Affiliation(s)
- Maor Asher
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Rémy Jouclas
- Laboratoire de Chimie des Polymères, Université Libre de Bruxelles (ULB), 1050 Brussels, Belgium
| | - Marco Bardini
- Laboratory for Chemistry of Novel Materials, University of Mons, 7000 Mons, Belgium
| | - Yael Diskin-Posner
- Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Nitzan Kahn
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Roman Korobko
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Alan R. Kennedy
- Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow G1 1XL, United Kingdom
| | - Lygia Silva de Moraes
- Laboratoire de Chimie des Polymères, Université Libre de Bruxelles (ULB), 1050 Brussels, Belgium
| | - Guillaume Schweicher
- Laboratoire de Chimie des Polymères, Université Libre de Bruxelles (ULB), 1050 Brussels, Belgium
| | - Jie Liu
- Laboratoire de Chimie des Polymères, Université Libre de Bruxelles (ULB), 1050 Brussels, Belgium
| | - David Beljonne
- Laboratory for Chemistry of Novel Materials, University of Mons, 7000 Mons, Belgium
| | - Yves Geerts
- Laboratoire de Chimie des Polymères, Université Libre de Bruxelles (ULB), 1050 Brussels, Belgium
- International Solvay Institutes for Physics and Chemistry, 1050 Brussels, Belgium
| | - Omer Yaffe
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 76100, Israel
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14
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Xie X, Troisi A. Evaluating the Electronic Structure of Coexisting Excitonic and Multiexcitonic States in Periodic Systems: Significance for Singlet Fission. J Chem Theory Comput 2021; 18:394-405. [PMID: 34902251 DOI: 10.1021/acs.jctc.1c00831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Singlet fission (SF) in organic molecular solids is an example of a process that is challenging to describe with the most common electronic structure approaches. It involves optically bright singlet excited states delocalized over many molecules, which could be efficiently treated by density functional theory, and multiexcitonic localized states that have to be studied with wavefunction methods, usually with small clusters considering their expensive computational costs. In this work, we propose a methodology to combine multiconfigurational wavefunction calculations with reduced Hamiltonian to investigate the electronic structure of large clusters or fully periodic systems. The method is applied to the prototypical SF materials tetracene and pentacene. The results allow one to study how states of different natures (excitonic, charge-transfer, and multiexcitonic) coexist and are contaminated by their couplings in large or periodic systems. Novel insights are therefore possible. For example, because the excitonic bands are relatively broad with respect to the multiexcitonic states, there are limited regions of the crystal momentum space where the transition between the two is more likely.
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Affiliation(s)
- Xiaoyu Xie
- Department of Chemistry, University of Liverpool, Liverpool L69 3BX, U.K
| | - Alessandro Troisi
- Department of Chemistry, University of Liverpool, Liverpool L69 3BX, U.K
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