Synthetic approaches to all-porphyrin nanorings
<p>We are interested in the synthesis of large, porphyrin-containing macrocycles to study their global aromaticity, as well as their application in molecular electronics. This thesis presents an exploration of synthetic approaches to all-porphyrin nanorings, in which every porphyrin unit is di...
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
2024
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| Subjects: |
| _version_ | 1824458622063607808 |
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| author | Field, J |
| author2 | Anderson, H |
| author_facet | Anderson, H Field, J |
| author_sort | Field, J |
| collection | OXFORD |
| description | <p>We are interested in the synthesis of large, porphyrin-containing macrocycles to study their global aromaticity, as well as their application in molecular electronics. This thesis presents an exploration of synthetic approaches to all-porphyrin nanorings, in which every porphyrin unit is directly bonded together.</p>
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<p>Chapter 1 outlines the properties of such porphyrin-based macrocycles that makes them desirable targets. In particular, the way in which an all-porphyrin nanoring may allow the further synthesis of porphyrin nanobelts is considered, and compared to the synthesis of carbon nanobelts reported by others. Such porphyrin nanobelts are expected to have very low HOMO–LUMO gaps, and strong radial π-conjugation.</p>
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<p>The concept of template-directed synthesis is also explained, which has enabled the construction of ethyne- and butadiyne-linked porphyrin nanorings in our group, through bending of the relevant linear oligomer into a cyclic conformation. However, construction of directly-linked porphyrin-porphyrin bonds under the standard oxidative coupling conditions used to construct the linear oligomers appears to be incompatible with this template-directed approach. Consequently, other strategies must be explored in order to synthesize our desired all-porphyrin nanorings.</p>
<br>
<p>In Chapter 2, we explore the first such strategy, involving the use of an end-differentiated linear all-porphyrin oligomer – one in which a tether was attached to the side chains of both terminal porphyrins. Under template-directed conditions, the linear oligomer is bent into a cyclic conformation, holding those tethers in close spatial proximity. These tethers could then react together, keeping the oligomer in a cyclic conformation that persists even after removal of the template. This could be performed using linear precursors with a range of lengths, giving a family of related macrocycles. The reasons behind the inability to convert these macrocycles into the desired all-porphyrin nanoring will be explained.</p>
<br>
<p>In Chapter 3, both template-directed Yamamoto coupling and template-directed Suzuki cross coupling approaches were explored, making use of the lessons learned from the tether-based approach. The Suzuki strategy was successful in synthesizing a range of different sized all-porphyrin nanorings, but the reaction was highly sensitive to a range of difficult-to-control factors, as well as significant purification issues. This ultimately resulted in this method being insufficiently repeatable and scalable.</p>
<br>
<p>In Chapter 4, we build on all of the lessons learned from the previous strategies, in that using easier-to-synthesize shorter linear precursors, and ideally utilizing template-free conditions to improve the purification, may be necessary. We tested a coupling strategy involving bis-chlorogold phosphino complexes, recently used in the facile synthesis of [<em>N</em>]cycloparaphenylenes ([<em>N</em>]CPPs) and other macrocycles. We obtained evidence suggesting the successful construction of the gold-porphyrin intermediate macrocycle, but all attempts at reductive elimination from this to give our desired all-porphyrin nanoring were unsuccessful.</p>
<br>
<p>Lastly in Chapter 5, a new project is explored, in which we present the synthesis towards electron-rich and electron-deficient porphyrin monomers for their use in redox-gated single-molecule conductance measurements. We want to use these as models to understand how to control the charge transport through a molecule using redox-switching as the external control modulus.</p> |
| first_indexed | 2025-02-19T04:28:49Z |
| format | Thesis |
| id | oxford-uuid:b39ad83e-ce2b-48a8-b6b8-8831c535931c |
| institution | University of Oxford |
| language | English |
| last_indexed | 2025-02-19T04:28:49Z |
| publishDate | 2024 |
| record_format | dspace |
| spelling | oxford-uuid:b39ad83e-ce2b-48a8-b6b8-8831c535931c2024-12-09T16:11:19ZSynthetic approaches to all-porphyrin nanoringsThesishttp://purl.org/coar/resource_type/c_db06uuid:b39ad83e-ce2b-48a8-b6b8-8831c535931cTemplate-directed synthesisPorphyrinsSupramolecular chemistryChemistryEnglishHyrax Deposit2024Field, JAnderson, H<p>We are interested in the synthesis of large, porphyrin-containing macrocycles to study their global aromaticity, as well as their application in molecular electronics. This thesis presents an exploration of synthetic approaches to all-porphyrin nanorings, in which every porphyrin unit is directly bonded together.</p> <br> <p>Chapter 1 outlines the properties of such porphyrin-based macrocycles that makes them desirable targets. In particular, the way in which an all-porphyrin nanoring may allow the further synthesis of porphyrin nanobelts is considered, and compared to the synthesis of carbon nanobelts reported by others. Such porphyrin nanobelts are expected to have very low HOMO–LUMO gaps, and strong radial π-conjugation.</p> <br> <p>The concept of template-directed synthesis is also explained, which has enabled the construction of ethyne- and butadiyne-linked porphyrin nanorings in our group, through bending of the relevant linear oligomer into a cyclic conformation. However, construction of directly-linked porphyrin-porphyrin bonds under the standard oxidative coupling conditions used to construct the linear oligomers appears to be incompatible with this template-directed approach. Consequently, other strategies must be explored in order to synthesize our desired all-porphyrin nanorings.</p> <br> <p>In Chapter 2, we explore the first such strategy, involving the use of an end-differentiated linear all-porphyrin oligomer – one in which a tether was attached to the side chains of both terminal porphyrins. Under template-directed conditions, the linear oligomer is bent into a cyclic conformation, holding those tethers in close spatial proximity. These tethers could then react together, keeping the oligomer in a cyclic conformation that persists even after removal of the template. This could be performed using linear precursors with a range of lengths, giving a family of related macrocycles. The reasons behind the inability to convert these macrocycles into the desired all-porphyrin nanoring will be explained.</p> <br> <p>In Chapter 3, both template-directed Yamamoto coupling and template-directed Suzuki cross coupling approaches were explored, making use of the lessons learned from the tether-based approach. The Suzuki strategy was successful in synthesizing a range of different sized all-porphyrin nanorings, but the reaction was highly sensitive to a range of difficult-to-control factors, as well as significant purification issues. This ultimately resulted in this method being insufficiently repeatable and scalable.</p> <br> <p>In Chapter 4, we build on all of the lessons learned from the previous strategies, in that using easier-to-synthesize shorter linear precursors, and ideally utilizing template-free conditions to improve the purification, may be necessary. We tested a coupling strategy involving bis-chlorogold phosphino complexes, recently used in the facile synthesis of [<em>N</em>]cycloparaphenylenes ([<em>N</em>]CPPs) and other macrocycles. We obtained evidence suggesting the successful construction of the gold-porphyrin intermediate macrocycle, but all attempts at reductive elimination from this to give our desired all-porphyrin nanoring were unsuccessful.</p> <br> <p>Lastly in Chapter 5, a new project is explored, in which we present the synthesis towards electron-rich and electron-deficient porphyrin monomers for their use in redox-gated single-molecule conductance measurements. We want to use these as models to understand how to control the charge transport through a molecule using redox-switching as the external control modulus.</p> |
| spellingShingle | Template-directed synthesis Porphyrins Supramolecular chemistry Chemistry Field, J Synthetic approaches to all-porphyrin nanorings |
| title | Synthetic approaches to all-porphyrin nanorings |
| title_full | Synthetic approaches to all-porphyrin nanorings |
| title_fullStr | Synthetic approaches to all-porphyrin nanorings |
| title_full_unstemmed | Synthetic approaches to all-porphyrin nanorings |
| title_short | Synthetic approaches to all-porphyrin nanorings |
| title_sort | synthetic approaches to all porphyrin nanorings |
| topic | Template-directed synthesis Porphyrins Supramolecular chemistry Chemistry |
| work_keys_str_mv | AT fieldj syntheticapproachestoallporphyrinnanorings |