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Riley DB, Meredith P, Armin A. Exciton diffusion in organic semiconductors: precision and pitfalls. NANOSCALE 2024. [PMID: 39171513 DOI: 10.1039/d4nr02467b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/23/2024]
Abstract
Nanometer exciton diffusion is a fundamental process important in virtually all applications of organic semiconductors. Many measurement techniques have been developed to measure exciton diffusion length (LD) at the nanometer scale; however, these techniques have common challenges that the community has worked for decades to overcome. In this perspective, we lay out the principal challenges researchers need to overcome to obtain an accurate measurement of LD. We then examine the most common techniques used to measure LD with respect to these challenges and describe solutions developed to overcome them. This analysis leads to the suggestion that static quenching techniques underestimate LD due to uncertainties in the quenching behavior, while time-resolved exciton-exciton annihilation (EEA) techniques overestimate LD based on experimental conditions, we advance steady-state EEA techniques as an alternative that overcome many of the challenges of these other techniques while preserving accuracy. We support this hypothesis with a meta-analysis of LD measured across various organic semiconductors and measurement techniques. We intend this investigation to provide a framework for researchers to interpret and compare findings across measurement techniques and to guide researchers on how to obtain the most accurate results for each technique in question.
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Affiliation(s)
- Drew B Riley
- Sustainable Advanced Materials (Sêr-SAM), Centre for Integrative Semiconductor Materials (CISM), Department of Physics, Swansea University Bay Campus, Swansea SA1 8EN, UK.
| | - Paul Meredith
- Sustainable Advanced Materials (Sêr-SAM), Centre for Integrative Semiconductor Materials (CISM), Department of Physics, Swansea University Bay Campus, Swansea SA1 8EN, UK.
| | - Ardalan Armin
- Sustainable Advanced Materials (Sêr-SAM), Centre for Integrative Semiconductor Materials (CISM), Department of Physics, Swansea University Bay Campus, Swansea SA1 8EN, UK.
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2
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Gharbi AM, Biswas DS, Crégut O, Malý P, Didier P, Klymchenko A, Léonard J. Exciton annihilation and diffusion length in disordered multichromophoric nanoparticles. NANOSCALE 2024; 16:11550-11563. [PMID: 38868990 DOI: 10.1039/d4nr00325j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2024]
Abstract
Efficient exciton transport is the essential property of natural and synthetic light-harvesting (LH) devices. Here we investigate exciton transport properties in LH organic polymer nanoparticles (ONPs) of 40 nm diameter. The ONPs are loaded with a rhodamine B dye derivative and bulky counterion, enabling dye loadings as high as 0.3 M, while preserving fluorescence quantum yields larger than 30%. We use time-resolved fluorescence spectroscopy to monitor exciton-exciton annihilation (EEA) kinetics within the ONPs dispersed in water. We demonstrate that unlike the common practice for photoluminescence investigations of EEA, the non-uniform intensity profile of the excitation light pulse must be taken into account to analyse reliably intensity-dependent population dynamics. Alternatively, a simple confocal detection scheme is demonstrated, which enables (i) retrieving the correct value for the bimolecular EEA rate which would otherwise be underestimated by a typical factor of three, and (ii) revealing minor EEA by-products otherwise unnoticed. Considering the ONPs as homogeneous rigid solutions of weakly interacting dyes, we postulate an incoherent exciton hoping mechanism to infer a diffusion constant exceeding 0.003 cm2 s-1 and a diffusion length as large as 70 nm. This work demonstrates the success of the present ONP design strategy at engineering efficient exciton transport in disordered multichromophoric systems.
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Affiliation(s)
| | | | - Olivier Crégut
- IPCMS, Université de Strasbourg - CNRS, Strasbourg, France.
| | - Pavel Malý
- Charles University, Prague, Czech Republic
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3
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Li S, Wei W, Chi K, Ferguson CTJ, Zhao Y, Zhang KAI. Promoting Photocatalytic Direct C-H Difluoromethylation of Heterocycles using Synergistic Dual-Active-Centered Covalent Organic Frameworks. J Am Chem Soc 2024; 146:12386-12394. [PMID: 38500309 PMCID: PMC11082899 DOI: 10.1021/jacs.3c12880] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 03/04/2024] [Accepted: 03/05/2024] [Indexed: 03/20/2024]
Abstract
Difluoromethylation reactions are increasingly important for the creation of fluorine-containing heterocycles, which are core groups in a diverse range of biologically and pharmacologically active ingredients. Ideally, this typically challenging reaction could be performed photocatalytically under mild conditions. To achieve this separation of redox processes would be required for the efficient generation of difluoromethyl radicals and the reduction of oxygen. A covalent organic framework photocatalytic material was, therefore, designed with dual reactive centers. Here, anthracene was used as a reduction site and benzothiadiazole was used as an oxidation site, distributed in a tristyryl triazine framework. Efficient charge separation was ensured by the superior electron-donating and -accepting abilities of the dual centers, creating long-lived photogenerated electron-hole pairs. Photocatalytic difluoromethylation of 16 compounds with high yields and remarkable functional group tolerance was demonstrated; compounds included bioactive molecules such as xanthine and uracil. The structure-function relationship of the dual-active-center photocatalyst was investigated through electron spin resonance, femtosecond transient absorption spectroscopy, and density functional theory calculations.
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Affiliation(s)
- Sizhe Li
- Department
of Materials Science, Fudan University, 200433 Shanghai, P. R. China
| | - Wenxin Wei
- Department
of Materials Science, Fudan University, 200433 Shanghai, P. R. China
| | - Kai Chi
- Department
of Materials Science, Fudan University, 200433 Shanghai, P. R. China
| | - Calum T. J. Ferguson
- Max
Planck Institute for Polymer Research, 55128 Mainz, Germany
- School
of Chemistry, University of Birmingham, University Road W, Birmingham B15 2TT, United Kingdom
| | - Yan Zhao
- Department
of Materials Science, Fudan University, 200433 Shanghai, P. R. China
| | - Kai A. I. Zhang
- Department
of Materials Science, Fudan University, 200433 Shanghai, P. R. China
- Max
Planck Institute for Polymer Research, 55128 Mainz, Germany
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4
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Hume PA, Price MB, Hodgkiss JM. New Avenues for Organic Solar Cells Using Intrinsically Charge-Generating Materials. JACS AU 2024; 4:1295-1302. [PMID: 38665646 PMCID: PMC11040696 DOI: 10.1021/jacsau.4c00046] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/10/2024] [Revised: 03/03/2024] [Accepted: 03/04/2024] [Indexed: 04/28/2024]
Abstract
The molecular electron acceptor material Y6 has been a key part of the most recent surge in organic solar cell sunlight-to-electricity power conversion efficiency, which is now approaching 20%. Numerous studies have sought to understand the fundamental photophysical reasons for the exceptional performance of Y6 and its growing family of structural derivatives. Though significant uncertainty about several details remains, many have concluded that initially photogenerated excited states rapidly convert into electron-hole charge pairs in the neat material. These charge pairs are characterized by location of the electron and hole on different Y6 molecules, in contrast to the Frenkel excitons that dominate the behavior of most organic semiconductor materials. Here, we summarize the current state of knowledge regarding Y6 photophysics and the key observations that have led to it. We then link this understanding to other advances, such as the role of quadrupolar fields in donor-acceptor blends, and the importance of molecular interactions and organization in providing the structural basis for Y6's properties. Finally, we turn our attention to ways of making use of the new photophysics of Y6, and suggest molecular doping, crystal structure tuning, and electric field engineering as promising avenues for future exploration.
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Affiliation(s)
- Paul A. Hume
- School
of Chemical and Physical Sciences, Victoria
University of Wellington, Wellington, 6012, New Zealand
- MacDiarmid
Institute for Advanced Materials and Nanotechnology, Wellington, 6012, New Zealand
| | - Michael B. Price
- School
of Chemistry, University of Bristol, Bristol, BS8 1TS, United Kingdom
| | - Justin M. Hodgkiss
- School
of Chemical and Physical Sciences, Victoria
University of Wellington, Wellington, 6012, New Zealand
- MacDiarmid
Institute for Advanced Materials and Nanotechnology, Wellington, 6012, New Zealand
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5
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Citty B, Lynd JK, Gera T, Varvelo L, Raccah DIGB. MesoHOPS: Size-invariant scaling calculations of multi-excitation open quantum systems. J Chem Phys 2024; 160:144118. [PMID: 38619062 DOI: 10.1063/5.0197825] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2024] [Accepted: 03/11/2024] [Indexed: 04/16/2024] Open
Abstract
The photoexcitation dynamics of molecular materials on the 10-100 nm length scale depend on complex interactions between electronic and vibrational degrees of freedom, rendering exact calculations difficult or intractable. The adaptive Hierarchy of Pure States (adHOPS) is a formally exact method that leverages the locality imposed by interactions between thermal environments and electronic excitations to achieve size-invariant scaling calculations for single-excitation processes in systems described by a Frenkel-Holstein Hamiltonian. Here, we extend adHOPS to account for arbitrary couplings between thermal environments and vertical excitation energies, enabling formally exact, size-invariant calculations that involve multiple excitations or states with shared thermal environments. In addition, we introduce a low-temperature correction and an effective integration of the noise to reduce the computational expense of including ultrafast vibrational relaxation in Hierarchy of Pure States (HOPS) simulations. We present these advances in the latest version of the open-source MesoHOPS library and use MesoHOPS to characterize charge separation at a one-dimensional organic heterojunction when both the electron and hole are mobile.
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Affiliation(s)
- Brian Citty
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
| | - Jacob K Lynd
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
| | - Tarun Gera
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
| | - Leonel Varvelo
- Department of Chemistry, Southern Methodist University, PO Box 750314 Dallas, Texas 75205, USA
| | - Doran I G B Raccah
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
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Brey D, Burghardt I. Coherent Transient Localization Mechanism of Interchain Exciton Transport in Regioregular P3HT: A Quantum-Dynamical Study. J Phys Chem Lett 2024; 15:1836-1845. [PMID: 38334949 DOI: 10.1021/acs.jpclett.3c03290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2024]
Abstract
Transient localization has been proposed as a transport mechanism in organic materials, for both charge carriers and excitons. Here, we characterize a quantum coherent transient localization mechanism using full quantum simulations of an H-aggregated model system representative of regioregular poly(3-hexylthiophene) (rrP3HT). A Frenkel-Holstein Hamiltonian parametrized from first principles is considered, including local high-frequency modes and anharmonic, site-correlated interchain modes. Quantum-dynamical calculations are carried out using the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method for a 13-site system with 195 vibrational modes, under periodic boundary conditions. It is shown that temporary localization of exciton polarons alternates with resonant transfer driven by interchain modes. While the transport process is mainly determined by exciton-polarons at the low-energy band edge, persistent coupling with the excitonic manifold is observed, giving rise to a nonadiabatic excitonic flux. This elementary transport mechanism remains preserved for limited static disorder and gives way to Anderson localization when the static disorder becomes dominant.
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Affiliation(s)
- Dominik Brey
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt, Germany
| | - Irene Burghardt
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt, Germany
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7
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Baxter JM, Koay CS, Xu D, Cheng SW, Tulyagankhodjaev JA, Shih P, Roy X, Delor M. Coexistence of Incoherent and Ultrafast Coherent Exciton Transport in a Two-Dimensional Superatomic Semiconductor. J Phys Chem Lett 2023; 14:10249-10256. [PMID: 37938804 DOI: 10.1021/acs.jpclett.3c02286] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2023]
Abstract
Fully leveraging the remarkable properties of low-dimensional semiconductors requires developing a deep understanding of how their structure and disorder affect the flow of electronic energy. Here, we study exciton transport in single crystals of the two-dimensional superatomic semiconductor CsRe6Se8I3, which straddles a photophysically rich yet elusive intermediate electronic-coupling regime. Using femtosecond scattering microscopy to directly image exciton transport in CsRe6Se8I3, we reveal the rare coexistence of coherent and incoherent exciton transport, leading to either persistent or transient electronic delocalization depending on temperature. Notably, coherent excitons exhibit ballistic transport at speeds approaching an extraordinary 1600 km/s over 300 fs. Such fast transport is mediated by J-aggregate-like superradiance, owing to the anisotropic structure and long-range order of CsRe6Se8I3. Our results establish superatomic crystals as ideal platforms for studying the intermediate electronic-coupling regime in highly ordered environments, in this case displaying long-range electronic delocalization, ultrafast energy flow, and a tunable dual transport regime.
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Affiliation(s)
- James M Baxter
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Christie S Koay
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Ding Xu
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Shan-Wen Cheng
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | | | - Petra Shih
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Xavier Roy
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Milan Delor
- Department of Chemistry, Columbia University, New York, New York 10027, United States
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Müller K, Schellhammer KS, Gräßler N, Debnath B, Liu F, Krupskaya Y, Leo K, Knupfer M, Ortmann F. Directed exciton transport highways in organic semiconductors. Nat Commun 2023; 14:5599. [PMID: 37699907 PMCID: PMC10497625 DOI: 10.1038/s41467-023-41044-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Accepted: 08/21/2023] [Indexed: 09/14/2023] Open
Abstract
Exciton bandwidths and exciton transport are difficult to control by material design. We showcase the intriguing excitonic properties in an organic semiconductor material with specifically tailored functional groups, in which extremely broad exciton bands in the near-infrared-visible part of the electromagnetic spectrum are observed by electron energy loss spectroscopy and theoretically explained by a close contact between tightly packing molecules and by their strong interactions. This is induced by the donor-acceptor type molecular structure and its resulting crystal packing, which induces a remarkable anisotropy that should lead to a strongly directed transport of excitons. The observations and detailed understanding of the results yield blueprints for the design of molecular structures in which similar molecular features might be used to further explore the tunability of excitonic bands and pave a way for organic materials with strongly enhanced transport and built-in control of the propagation direction.
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Affiliation(s)
- Kai Müller
- Center for Advancing Electronics Dresden, Technische Universität Dresden, 01062, Dresden, Germany
- Institut für Theoretische Physik, Technische Universität Dresden, 01062, Dresden, Germany
| | - Karl S Schellhammer
- Center for Advancing Electronics Dresden, Technische Universität Dresden, 01062, Dresden, Germany
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, 01062, Dresden, Germany
| | - Nico Gräßler
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, 01062, Dresden, Germany
- Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstr. 20, 01069, Dresden, Germany
| | - Bipasha Debnath
- Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstr. 20, 01069, Dresden, Germany
| | - Fupin Liu
- Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstr. 20, 01069, Dresden, Germany
| | - Yulia Krupskaya
- Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstr. 20, 01069, Dresden, Germany
| | - Karl Leo
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, 01062, Dresden, Germany
| | - Martin Knupfer
- Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstr. 20, 01069, Dresden, Germany
| | - Frank Ortmann
- Center for Advancing Electronics Dresden, Technische Universität Dresden, 01062, Dresden, Germany.
- Department of Chemistry, TUM School of Natural Sciences, Technische Universität München, Lichtenbergstr. 4, 85748, Garching b. München, Germany.
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Toldo JM, do Casal MT, Ventura E, do Monte SA, Barbatti M. Surface hopping modeling of charge and energy transfer in active environments. Phys Chem Chem Phys 2023; 25:8293-8316. [PMID: 36916738 PMCID: PMC10034598 DOI: 10.1039/d3cp00247k] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/05/2023]
Abstract
An active environment is any atomic or molecular system changing a chromophore's nonadiabatic dynamics compared to the isolated molecule. The action of the environment on the chromophore occurs by changing the potential energy landscape and triggering new energy and charge flows unavailable in the vacuum. Surface hopping is a mixed quantum-classical approach whose extreme flexibility has made it the primary platform for implementing novel methodologies to investigate the nonadiabatic dynamics of a chromophore in active environments. This Perspective paper surveys the latest developments in the field, focusing on charge and energy transfer processes.
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Affiliation(s)
| | | | - Elizete Ventura
- Departamento de Química, CCEN, Universidade Federal da Paraíba, 58059-900, João Pessoa, Brazil.
| | - Silmar A do Monte
- Departamento de Química, CCEN, Universidade Federal da Paraíba, 58059-900, João Pessoa, Brazil.
| | - Mario Barbatti
- Aix-Marseille University, CNRS, ICR, Marseille, France.
- Institut Universitaire de France, 75231, Paris, France
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