Probing Exciton Dynamics in Metal–Organic Frameworks
Bound electron–hole pairs, known as excitons, are key carriers of energy during a material’s interaction with light. Therefore extending understanding and control over exciton dynamics can potentially break the bottlenecks that currently limit solar energy harvesting technologies. However, design pr...
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| Format: | Thesis |
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Massachusetts Institute of Technology
2023
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| Online Access: | https://hdl.handle.net/1721.1/152133 https://orcid.org/0000-0001-8824-7128 |
| _version_ | 1826204899517399040 |
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| author | Wan, Ruomeng |
| author2 | Dincă, Mircea |
| author_facet | Dincă, Mircea Wan, Ruomeng |
| author_sort | Wan, Ruomeng |
| collection | MIT |
| description | Bound electron–hole pairs, known as excitons, are key carriers of energy during a material’s interaction with light. Therefore extending understanding and control over exciton dynamics can potentially break the bottlenecks that currently limit solar energy harvesting technologies. However, design principles for accessing desired exciton transfer and conversion pathways remain unclear, as these dynamics are often tangled with a mixture of interactions both among excitons and with the surrounding environment. To address this challenge, efforts in this thesis center around developing strategies for tuning exciton dynamics using metal–organic frameworks (MOFs) as a scaffold. Independent synthetic handles within MOFs will be mapped with the structural and electronic variables that impact exciton–exciton, exciton–vibrational, and exciton–photon interactions. Chapter 1 introduces the fundamental principles underlying these three types of interactions experienced by excitons in MOFs. The perception of MOFs will be expanded beyond the traditional image of their crystal structure to capture MOFs’ nuclear degrees of freedom, dielectric environment, and macroscopic morphology, which are factors that will be further explored in the following chapters. Chapter 2 demonstrates that MOFs’ metric structure is suited for tuning exciton–exciton interactions that occur via resonant dipole coupling. Due to the angular sensitivity of these interactions, a paddlewheel pillared MOF structure effectively blocks parasitic singlet energy transfer from a pyrene donor to a porphyrin acceptor by anchoring their transition dipoles at 90° to each other. Chapter 3 brings MOFs’ nuclear degrees of freedom into consideration, and identifies spectral footprints left by excitons’ coupling to the intramolecular vibration of the organic building units. These vibronic signatures are applied as a spectral handle for extracting the trend of excitonic coupling strength in a series of perylene diimide (PDI)-based MOF-74 analogs with different metal ions (Mn2+, Ni2+, Zn2+). A correlation between the excitonic coupling strength and the metal ions’ polarizability points to the inorganic moieties’ potential role in mediating the dielectric environment experienced by the excitons. Chapter 4 zooms out of the light–MOF interactions occurring at the molecular level to highlight the influence of the macroscopic morphology of MOF crystallites. A dipole orientation-dependent waveguide effect detected in bichromophoric MOF microplates reveals that excitons’ transition dipoles in MOFs can be inherently aligned with the reflecting surfaces of their surrounding microcavity, which enables potential control over excitons’ interaction with the waveguide modes confined in the crystal. Broader implications and future possibilities unlocked by these observations will be discussed. |
| first_indexed | 2024-09-23T13:02:49Z |
| format | Thesis |
| id | mit-1721.1/152133 |
| institution | Massachusetts Institute of Technology |
| last_indexed | 2024-09-23T13:02:49Z |
| publishDate | 2023 |
| publisher | Massachusetts Institute of Technology |
| record_format | dspace |
| spelling | mit-1721.1/1521332023-09-14T03:29:21Z Probing Exciton Dynamics in Metal–Organic Frameworks Wan, Ruomeng Dincă, Mircea Tisdale, William A. Massachusetts Institute of Technology. Department of Chemistry Bound electron–hole pairs, known as excitons, are key carriers of energy during a material’s interaction with light. Therefore extending understanding and control over exciton dynamics can potentially break the bottlenecks that currently limit solar energy harvesting technologies. However, design principles for accessing desired exciton transfer and conversion pathways remain unclear, as these dynamics are often tangled with a mixture of interactions both among excitons and with the surrounding environment. To address this challenge, efforts in this thesis center around developing strategies for tuning exciton dynamics using metal–organic frameworks (MOFs) as a scaffold. Independent synthetic handles within MOFs will be mapped with the structural and electronic variables that impact exciton–exciton, exciton–vibrational, and exciton–photon interactions. Chapter 1 introduces the fundamental principles underlying these three types of interactions experienced by excitons in MOFs. The perception of MOFs will be expanded beyond the traditional image of their crystal structure to capture MOFs’ nuclear degrees of freedom, dielectric environment, and macroscopic morphology, which are factors that will be further explored in the following chapters. Chapter 2 demonstrates that MOFs’ metric structure is suited for tuning exciton–exciton interactions that occur via resonant dipole coupling. Due to the angular sensitivity of these interactions, a paddlewheel pillared MOF structure effectively blocks parasitic singlet energy transfer from a pyrene donor to a porphyrin acceptor by anchoring their transition dipoles at 90° to each other. Chapter 3 brings MOFs’ nuclear degrees of freedom into consideration, and identifies spectral footprints left by excitons’ coupling to the intramolecular vibration of the organic building units. These vibronic signatures are applied as a spectral handle for extracting the trend of excitonic coupling strength in a series of perylene diimide (PDI)-based MOF-74 analogs with different metal ions (Mn2+, Ni2+, Zn2+). A correlation between the excitonic coupling strength and the metal ions’ polarizability points to the inorganic moieties’ potential role in mediating the dielectric environment experienced by the excitons. Chapter 4 zooms out of the light–MOF interactions occurring at the molecular level to highlight the influence of the macroscopic morphology of MOF crystallites. A dipole orientation-dependent waveguide effect detected in bichromophoric MOF microplates reveals that excitons’ transition dipoles in MOFs can be inherently aligned with the reflecting surfaces of their surrounding microcavity, which enables potential control over excitons’ interaction with the waveguide modes confined in the crystal. Broader implications and future possibilities unlocked by these observations will be discussed. Ph.D. 2023-09-13T18:07:32Z 2023-09-13T18:07:32Z 2023-06 2023-09-05T20:09:27.498Z Thesis https://hdl.handle.net/1721.1/152133 https://orcid.org/0000-0001-8824-7128 Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) Copyright retained by author(s) https://creativecommons.org/licenses/by-sa/4.0/ application/pdf Massachusetts Institute of Technology |
| spellingShingle | Wan, Ruomeng Probing Exciton Dynamics in Metal–Organic Frameworks |
| title | Probing Exciton Dynamics in Metal–Organic Frameworks |
| title_full | Probing Exciton Dynamics in Metal–Organic Frameworks |
| title_fullStr | Probing Exciton Dynamics in Metal–Organic Frameworks |
| title_full_unstemmed | Probing Exciton Dynamics in Metal–Organic Frameworks |
| title_short | Probing Exciton Dynamics in Metal–Organic Frameworks |
| title_sort | probing exciton dynamics in metal organic frameworks |
| url | https://hdl.handle.net/1721.1/152133 https://orcid.org/0000-0001-8824-7128 |
| work_keys_str_mv | AT wanruomeng probingexcitondynamicsinmetalorganicframeworks |