Fused porphyrin oligomers as molecular wires and approaches to related nanobelts
<p>Triply-linked (edge-fused) porphyrin oligomers with strongly coupled π orbitals can be used for studying long range charge transport, and are expected to be promising candidates for fabrication of electronic devices. This thesis details the synthesis, characterization and properties of a ra...
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| Övriga upphovsmän: | |
| Materialtyp: | Lärdomsprov |
| Språk: | English |
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2022
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| Ämnen: |
| _version_ | 1826313464481579008 |
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| author | Deng, J |
| author2 | Anderson, H |
| author_facet | Anderson, H Deng, J |
| author_sort | Deng, J |
| collection | OXFORD |
| description | <p>Triply-linked (edge-fused) porphyrin oligomers with strongly coupled π orbitals can be used for studying long range charge transport, and are expected to be promising candidates for fabrication of electronic devices. This thesis details the synthesis, characterization and properties of a range of linear fused porphyrin oligomers with different metals (zinc and nickel), and attempts toward the cyclic fused porphyrin oligomers (nanobelts).</p>
<p><strong>Chapter 1</strong> reviews the synthesis, electronic properties and charge transport studies of three classes of conjugated porphyrin oligomers which have been intensively investigated — butadiyne-linked, ethyne-linked and fused porphyrin oligomers. The single-molecule conductance studies on the linear oligomers, the template-directed synthesis of cyclic oligomers, and the global (anti)aromaticity of porphyrin nanorings are detailed.</p>
<p><strong>Chapter 2</strong> details the attempts toward the meso–meso singly-linked porphyrin nanorings and the related fused porphyrin nanobelts. Guided by computational modeling, we show that oligopyridyl templates can be used to bend the rod-like meso–meso singly-linked porphyrin oligomers into covalent nanorings. These nanorings consist of 24 porphyrin units, with a single butadiyne link. Their elliptical conformations have been probed by scanning tunneling microscopy. Upon photoexcitation, the template-free nanorings exhibit ultrafast excited state energy transfer (~8.5 ps) from the exciton-coupled meso–meso linked porphyrin array to the π-conjugated butadiyne-linked porphyrin dimer segment, which mimics the B850 ring in the natural light harvesting system. The successful synthesis of these rings also provides insight into the future works on making the singly-linked porphyrin nanorings and fused porphyrin nanobelts.</p>
<p><strong>Chapter 3</strong> presents new advances in synthesis and charge transport studies on a family of linear fused nickel(II) porphyrin oligomers up to an octamer. The molecular conductance is measured by STM break junction technique, in which the molecules are connected to gold electrodes via covalent C–Au contacts. The fused porphyrin octamer junctions (~8 nm in length) express low-bias molecular conductance ranging from 10–3 to 10–5 G0 that has been rarely observed in single-molecule junctions beyond 5 nm. This reflects the weakly distance-dependent attenuation feature for the fused porphyrin oligomers and the low effective contact resistance for the covalent C–Au contacts.</p>
<p><strong>Chapter 4</strong> studies the charge transport in a fused nickel(II) porphyrin octamer-graphene single-molecule transistor. We demonstrate how molecular and graphene transport pathways influence the overall device conductance and demonstrate that transport remains phase-coherent through a porphyrin octamer junction that is about 8 nm in length. We also investigate the relationship between the charge state of the molecule and its conductance — a three-fold increase of the conductance and the appearance of the Kondo resonance were observed upon oxidation of the porphyrin octamer to a radical cation.</p>
<p><strong>Chapter 5</strong> investigates the extent of polaron delocalization in the radical cations of fused zinc(II) porphyrin oligomers. The radical cations were generated in solution by chemical and electrochemical oxidation, and probed by UV‒vis‒NIR‒IR and EPR spectroscopies. We demonstrate that the polaron states in the fused porphyrin oligomers are coherently delocalized over 10 porphyrin units (≥ 8.5 nm in length). This is unprecedented for the extent of intrachain polaron delocalization in a π-conjugated organic material in solution. In addition to the polaron delocalization length, we also show that the fused zinc(II) porphyrin hexamer and longer oligomers are partially oxidized to form stable radical cations in air.</p> |
| first_indexed | 2024-09-25T04:13:48Z |
| format | Thesis |
| id | oxford-uuid:5b72d9a6-3d86-4b5e-93cd-284ab57ccd5e |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-09-25T04:13:48Z |
| publishDate | 2022 |
| record_format | dspace |
| spelling | oxford-uuid:5b72d9a6-3d86-4b5e-93cd-284ab57ccd5e2024-07-15T10:09:57ZFused porphyrin oligomers as molecular wires and approaches to related nanobeltsThesishttp://purl.org/coar/resource_type/c_db06uuid:5b72d9a6-3d86-4b5e-93cd-284ab57ccd5eChemistry, OrganicSupramolecular chemistryMaterials chemistryEnglishHyrax Deposit2022Deng, JAnderson, HBogani, LNuckolls, C<p>Triply-linked (edge-fused) porphyrin oligomers with strongly coupled π orbitals can be used for studying long range charge transport, and are expected to be promising candidates for fabrication of electronic devices. This thesis details the synthesis, characterization and properties of a range of linear fused porphyrin oligomers with different metals (zinc and nickel), and attempts toward the cyclic fused porphyrin oligomers (nanobelts).</p> <p><strong>Chapter 1</strong> reviews the synthesis, electronic properties and charge transport studies of three classes of conjugated porphyrin oligomers which have been intensively investigated — butadiyne-linked, ethyne-linked and fused porphyrin oligomers. The single-molecule conductance studies on the linear oligomers, the template-directed synthesis of cyclic oligomers, and the global (anti)aromaticity of porphyrin nanorings are detailed.</p> <p><strong>Chapter 2</strong> details the attempts toward the meso–meso singly-linked porphyrin nanorings and the related fused porphyrin nanobelts. Guided by computational modeling, we show that oligopyridyl templates can be used to bend the rod-like meso–meso singly-linked porphyrin oligomers into covalent nanorings. These nanorings consist of 24 porphyrin units, with a single butadiyne link. Their elliptical conformations have been probed by scanning tunneling microscopy. Upon photoexcitation, the template-free nanorings exhibit ultrafast excited state energy transfer (~8.5 ps) from the exciton-coupled meso–meso linked porphyrin array to the π-conjugated butadiyne-linked porphyrin dimer segment, which mimics the B850 ring in the natural light harvesting system. The successful synthesis of these rings also provides insight into the future works on making the singly-linked porphyrin nanorings and fused porphyrin nanobelts.</p> <p><strong>Chapter 3</strong> presents new advances in synthesis and charge transport studies on a family of linear fused nickel(II) porphyrin oligomers up to an octamer. The molecular conductance is measured by STM break junction technique, in which the molecules are connected to gold electrodes via covalent C–Au contacts. The fused porphyrin octamer junctions (~8 nm in length) express low-bias molecular conductance ranging from 10–3 to 10–5 G0 that has been rarely observed in single-molecule junctions beyond 5 nm. This reflects the weakly distance-dependent attenuation feature for the fused porphyrin oligomers and the low effective contact resistance for the covalent C–Au contacts.</p> <p><strong>Chapter 4</strong> studies the charge transport in a fused nickel(II) porphyrin octamer-graphene single-molecule transistor. We demonstrate how molecular and graphene transport pathways influence the overall device conductance and demonstrate that transport remains phase-coherent through a porphyrin octamer junction that is about 8 nm in length. We also investigate the relationship between the charge state of the molecule and its conductance — a three-fold increase of the conductance and the appearance of the Kondo resonance were observed upon oxidation of the porphyrin octamer to a radical cation.</p> <p><strong>Chapter 5</strong> investigates the extent of polaron delocalization in the radical cations of fused zinc(II) porphyrin oligomers. The radical cations were generated in solution by chemical and electrochemical oxidation, and probed by UV‒vis‒NIR‒IR and EPR spectroscopies. We demonstrate that the polaron states in the fused porphyrin oligomers are coherently delocalized over 10 porphyrin units (≥ 8.5 nm in length). This is unprecedented for the extent of intrachain polaron delocalization in a π-conjugated organic material in solution. In addition to the polaron delocalization length, we also show that the fused zinc(II) porphyrin hexamer and longer oligomers are partially oxidized to form stable radical cations in air.</p> |
| spellingShingle | Chemistry, Organic Supramolecular chemistry Materials chemistry Deng, J Fused porphyrin oligomers as molecular wires and approaches to related nanobelts |
| title | Fused porphyrin oligomers as molecular wires and approaches to related nanobelts |
| title_full | Fused porphyrin oligomers as molecular wires and approaches to related nanobelts |
| title_fullStr | Fused porphyrin oligomers as molecular wires and approaches to related nanobelts |
| title_full_unstemmed | Fused porphyrin oligomers as molecular wires and approaches to related nanobelts |
| title_short | Fused porphyrin oligomers as molecular wires and approaches to related nanobelts |
| title_sort | fused porphyrin oligomers as molecular wires and approaches to related nanobelts |
| topic | Chemistry, Organic Supramolecular chemistry Materials chemistry |
| work_keys_str_mv | AT dengj fusedporphyrinoligomersasmolecularwiresandapproachestorelatednanobelts |