Controlling charge and spin delocalization in porphyrin nanomaterials – synthesis and magnetic resonance studies
<p>The research presented in this thesis describes the synthesis and spectroscopic investigation of porphyrin nanomaterials with tailored electronic and magnetic properties. A detailed understanding of the factors that govern the distribution of charge and spin carriers in π-conjugated molecul...
| मुख्य लेखक: | |
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| अन्य लेखक: | |
| स्वरूप: | थीसिस |
| भाषा: | English |
| प्रकाशित: |
2024
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| _version_ | 1826314595779739648 |
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| author | Kopp, SM |
| author2 | Anderson, H |
| author_facet | Anderson, H Kopp, SM |
| author_sort | Kopp, SM |
| collection | OXFORD |
| description | <p>The research presented in this thesis describes the synthesis and spectroscopic investigation of porphyrin nanomaterials with tailored electronic and magnetic properties. A detailed understanding of the factors that govern the distribution of charge and spin carriers in π-conjugated molecules is important for the rational design of new materials with potential applications in molecular electronic, spintronic, and photonic devices. Electron paramagnetic resonance (EPR) spectroscopy, steady-state and transient optical absorption spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and quantum chemical calculations were employed throughout this thesis to study charge and spin delocalization.</p>
<p>The delocalization of radical cations in edge-fused porphyrin nanoribbons was investigated. Information about the extent of radical delocalization was obtained from the hyperfine couplings probed by continuous-wave (cw) and pulse EPR techniques. The trend in the wavelength of the lowest energy optical transitions provided additional information about the polaron delocalization. The results confirm coherent radical delocalization over more than ten porphyrin units, and a remarkably non-uniform distribution of the electron spin density. This is the most delocalized polaron, yet reported, in π-conjugated molecular materials.</p>
<p>The electron and spin transfer dynamics of the radical cation and photogenerated triplet states in a weakly coupled porphyrin dimer were studied. Variable-temperature cw-EPR spectroscopy demonstrated the presence of reversible, intramolecular electron transfers in the radical cations in fluid solution, and the localization of charge carriers in frozen solution. The hyperfine and zero–field splitting interactions of the photogenerated triplet state confirm the localization of the exciton on one porphyrin unit on the timescale of the EPR experiments. These findings are important for the design of new molecular spintronic materials.</p>
<p>The delocalization of photogenerated triplet excitons of anionic porphyrin wires was investigated. The triplet excited states exhibit substantially smaller zero–field splitting interactions and shorter lifetimes compared to the triplet states in the neutral porphyrin oligomers. These results demonstrate that photoexcitation of reduced porphyrin oligomers increases the spatial delocalization of triplet excitons, which leads to the formation of the most delocalized triplet excited states reported so far in one-dimensional π-conjugated molecular materials.</p>
<p>A new class of porphyrin nanoring complexes consisting of edge-fused and butadiynelinked porphyrin units was prepared by template-directed synthesis. The partially fused nanoring complexes exhibit a significantly stronger effective π-conjugation in comparison to previously investigated nanorings. The global charge delocalization and aromaticity of partially fused 8- and 12-porphyrin nanoring complexes were analyzed by NMR spectroscopy. Amplified global ring currents in agreement with Hückel’s rule were observed in the oxidized and reduced nanorings, which opens new avenues for the engineering of cyclic molecular wires.</p> |
| first_indexed | 2024-09-25T04:34:54Z |
| format | Thesis |
| id | oxford-uuid:558d0596-bbdb-4bb8-9c5d-e27ea94c5d70 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-09-25T04:34:54Z |
| publishDate | 2024 |
| record_format | dspace |
| spelling | oxford-uuid:558d0596-bbdb-4bb8-9c5d-e27ea94c5d702024-09-18T16:21:46ZControlling charge and spin delocalization in porphyrin nanomaterials – synthesis and magnetic resonance studiesThesishttp://purl.org/coar/resource_type/c_db06uuid:558d0596-bbdb-4bb8-9c5d-e27ea94c5d70EnglishHyrax Deposit2024Kopp, SMAnderson, HTimmel, C<p>The research presented in this thesis describes the synthesis and spectroscopic investigation of porphyrin nanomaterials with tailored electronic and magnetic properties. A detailed understanding of the factors that govern the distribution of charge and spin carriers in π-conjugated molecules is important for the rational design of new materials with potential applications in molecular electronic, spintronic, and photonic devices. Electron paramagnetic resonance (EPR) spectroscopy, steady-state and transient optical absorption spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and quantum chemical calculations were employed throughout this thesis to study charge and spin delocalization.</p> <p>The delocalization of radical cations in edge-fused porphyrin nanoribbons was investigated. Information about the extent of radical delocalization was obtained from the hyperfine couplings probed by continuous-wave (cw) and pulse EPR techniques. The trend in the wavelength of the lowest energy optical transitions provided additional information about the polaron delocalization. The results confirm coherent radical delocalization over more than ten porphyrin units, and a remarkably non-uniform distribution of the electron spin density. This is the most delocalized polaron, yet reported, in π-conjugated molecular materials.</p> <p>The electron and spin transfer dynamics of the radical cation and photogenerated triplet states in a weakly coupled porphyrin dimer were studied. Variable-temperature cw-EPR spectroscopy demonstrated the presence of reversible, intramolecular electron transfers in the radical cations in fluid solution, and the localization of charge carriers in frozen solution. The hyperfine and zero–field splitting interactions of the photogenerated triplet state confirm the localization of the exciton on one porphyrin unit on the timescale of the EPR experiments. These findings are important for the design of new molecular spintronic materials.</p> <p>The delocalization of photogenerated triplet excitons of anionic porphyrin wires was investigated. The triplet excited states exhibit substantially smaller zero–field splitting interactions and shorter lifetimes compared to the triplet states in the neutral porphyrin oligomers. These results demonstrate that photoexcitation of reduced porphyrin oligomers increases the spatial delocalization of triplet excitons, which leads to the formation of the most delocalized triplet excited states reported so far in one-dimensional π-conjugated molecular materials.</p> <p>A new class of porphyrin nanoring complexes consisting of edge-fused and butadiynelinked porphyrin units was prepared by template-directed synthesis. The partially fused nanoring complexes exhibit a significantly stronger effective π-conjugation in comparison to previously investigated nanorings. The global charge delocalization and aromaticity of partially fused 8- and 12-porphyrin nanoring complexes were analyzed by NMR spectroscopy. Amplified global ring currents in agreement with Hückel’s rule were observed in the oxidized and reduced nanorings, which opens new avenues for the engineering of cyclic molecular wires.</p> |
| spellingShingle | Kopp, SM Controlling charge and spin delocalization in porphyrin nanomaterials – synthesis and magnetic resonance studies |
| title | Controlling charge and spin delocalization in porphyrin nanomaterials – synthesis and magnetic resonance studies |
| title_full | Controlling charge and spin delocalization in porphyrin nanomaterials – synthesis and magnetic resonance studies |
| title_fullStr | Controlling charge and spin delocalization in porphyrin nanomaterials – synthesis and magnetic resonance studies |
| title_full_unstemmed | Controlling charge and spin delocalization in porphyrin nanomaterials – synthesis and magnetic resonance studies |
| title_short | Controlling charge and spin delocalization in porphyrin nanomaterials – synthesis and magnetic resonance studies |
| title_sort | controlling charge and spin delocalization in porphyrin nanomaterials synthesis and magnetic resonance studies |
| work_keys_str_mv | AT koppsm controllingchargeandspindelocalizationinporphyrinnanomaterialssynthesisandmagneticresonancestudies |