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Afrin S, Yang X, Morris AJ, Grumstrup EM. Rapid Exciton Transport and Structural Defects in Individual Porphyrinic Metal Organic Framework Microcrystals. J Am Chem Soc 2024; 146:4309-4313. [PMID: 38330249 PMCID: PMC10885150 DOI: 10.1021/jacs.3c12275] [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
To date, spectroscopic characterization of porphyrin-based metal organic frameworks (MOFs) has relied almost exclusively on ensemble techniques, which provide only structurally averaged insight into the functional properties of these promising photochemical platforms. This work employs time-resolved pump-probe microscopy to probe ultrafast dynamics in PCN-222 MOF single crystals. The simultaneous high spatial and temporal resolution of the technique enables the correlation of spectroscopic observables to both inter- and intracrystal structural heterogeneity. The pump-probe measurements show that significant differences in the excited state lifetime exist between individual PCN-222 crystals of an ensemble. On a single PCN-222 crystal, differences in excited state lifetime and photoluminescence quantum yield are found to correlate to microscale structural defects introduced at crystallization. Pump probe microscopy also enables the direct measurement of excited state transport. Imaging of exciton transport on individual MOF crystals reveals rapid, but subdiffusive exciton transport which slows on the 10s of ps time scale. Time-averaged exciton diffusion coefficients over the first 200 ps span a range of 0.27 to 1.0 cm2/s, indicating that excited states are rapidly transported through the porphyrin network of PCN-222 before being trapped. Together, these single-particle-resolved measurements provide important new insight into the role played by structural defects on the photochemical functionality of porphyrin-based MOFs.
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Affiliation(s)
- Sajia Afrin
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
- Montana Materials Science Program, Montana State University, Bozeman, Montana 59717, United States
| | - Xiaozhou Yang
- Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Amanda J Morris
- Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Erik M Grumstrup
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
- Montana Materials Science Program, Montana State University, Bozeman, Montana 59717, United States
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Wittmann B, Wiesneth S, Motamen S, Simon L, Serein-Spirau F, Reiter G, Hildner R. Energy transport and light propagation mechanisms in organic single crystals. J Chem Phys 2020; 153:144202. [PMID: 33086831 DOI: 10.1063/5.0019832] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Unambiguous information about spatiotemporal exciton dynamics in three-dimensional nanometer- to micrometer-sized organic structures is difficult to obtain experimentally. Exciton dynamics can be modified by annihilation processes, and different light propagation mechanisms can take place, such as active waveguiding and photon recycling. Since these various processes and mechanisms can lead to similar spectroscopic and microscopic signatures on comparable time scales, their discrimination is highly demanding. Here, we study individual organic single crystals grown from thiophene-based oligomers. We use time-resolved detection-beam scanning microscopy to excite a local singlet exciton population and monitor the subsequent broadening of the photoluminescence (PL) signal in space and on pico- to nanosecond time scales. Combined with Monte Carlo simulations, we were able to exclude photon recycling for our system, whereas leakage radiation upon active waveguiding leads to an apparent PL broadening of about 20% compared to the initial excitation profile. Exciton-exciton annihilation becomes important at high excitation fluence and apparently accelerates the exciton dynamics leading to apparently increased diffusion lengths. At low excitation fluences, the spatiotemporal PL broadening results from singlet exciton diffusion with diffusion lengths of up to 210 nm. Surprisingly, even in structurally highly ordered single crystals, the transport dynamics is subdiffusive and shows variations between different crystals, which we relate to varying degrees of static and dynamic electronic disorders.
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Affiliation(s)
- Bernd Wittmann
- Spectroscopy of Soft Matter, University of Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany
| | - Stephan Wiesneth
- Spectroscopy of Soft Matter, University of Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany
| | - Sajedeh Motamen
- Institute of Physics, University of Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, Germany
| | - Laurent Simon
- Université de Strasbourg (UdS)-Université de Haute Alsace (UHA), Institut de Science des Matériaux de Mulhouse (IS2M), UMR 7361-CNRS, 3bis rue Alfred Werner, 68093 Mulhouse, France
| | - Françoise Serein-Spirau
- Institut Charles Gerhardt de Montpellier, Université de Montpellier, Ecole Nationale Supérieure de Chimie de Montpellier, UMR 5353-CNRS, Equipe Architectures Moleculaires et Materiaux Nanostructures (AM2N), 8 Rue de l'Ecole Normale, 34090 Montpellier Cedex 05, France
| | - Günter Reiter
- Institute of Physics, University of Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, Germany
| | - Richard Hildner
- Spectroscopy of Soft Matter, University of Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany
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Pandya R, Chen RYS, Gu Q, Gorman J, Auras F, Sung J, Friend R, Kukura P, Schnedermann C, Rao A. Femtosecond Transient Absorption Microscopy of Singlet Exciton Motion in Side-Chain Engineered Perylene-Diimide Thin Films. J Phys Chem A 2020; 124:2721-2730. [PMID: 32130861 PMCID: PMC7132576 DOI: 10.1021/acs.jpca.0c00346] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Revised: 03/04/2020] [Indexed: 12/21/2022]
Abstract
We present a statistical analysis of femtosecond transient absorption microscopy applied to four different organic semiconductor thin films based on perylene-diimide (PDI). By achieving a temporal resolution of 12 fs with simultaneous sub-10 nm spatial precision, we directly probe the underlying exciton transport characteristics within 3 ps after photoexcitation free of model assumptions. Our study reveals sub-picosecond coherent exciton transport (12-45 cm2 s-1) followed by a diffusive phase of exciton transport (3-17 cm2 s-1). A comparison between the different films suggests that the exciton transport in the studied materials is intricately linked to their nanoscale morphology, with PDI films that form large crystalline domains exhibiting the largest diffusion coefficients and transport lengths. Our study demonstrates the advantages of directly studying ultrafast transport properties at the nanometer length scale and highlights the need to examine nanoscale morphology when investigating exciton transport in organic as well as inorganic semiconductors.
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Affiliation(s)
- Raj Pandya
- Department
of Physics, Cavendish Laboratory, University
of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K.
| | - Richard Y. S. Chen
- Department
of Physics, Cavendish Laboratory, University
of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K.
| | - Qifei Gu
- Department
of Physics, Cavendish Laboratory, University
of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K.
| | - Jeffrey Gorman
- Department
of Physics, Cavendish Laboratory, University
of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K.
| | - Florian Auras
- Department
of Physics, Cavendish Laboratory, University
of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K.
| | - Jooyoung Sung
- Department
of Physics, Cavendish Laboratory, University
of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K.
| | - Richard Friend
- Department
of Physics, Cavendish Laboratory, University
of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K.
| | - Philipp Kukura
- Physical
and Theoretical Chemistry Laboratory, Oxford
University, South Parks Road, Oxford OX1 3QZ, U.K.
| | - Christoph Schnedermann
- Department
of Physics, Cavendish Laboratory, University
of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K.
| | - Akshay Rao
- Department
of Physics, Cavendish Laboratory, University
of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K.
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