Photoactive Iron N-Heterocyclic Carbene Complexes : From Design to Photoredox Catalysis
(2024)- Abstract
- Recent years have seen a surge to develop first-row transition metal complexes with photophysics and photochemistry similar to those of noble metals, such as ruthenium and iridium. The reason for this is obvious, looking at their relative abundance. Iron stands out as the most abundant transition metal on earth, and is positioned right above ruthenium in the periodic table.
The aim of this thesis has been to design and synthesise new photoactive iron complexes, and to apply these in artificial photosynthesis and photoredox catalysis. The strategy for both the new complexes and existing complexes has been to use N-heterocyclic carbenes (NHC) as strongly σ-donating ligands, to increase the ligand field splitting. This raises the... (More) - Recent years have seen a surge to develop first-row transition metal complexes with photophysics and photochemistry similar to those of noble metals, such as ruthenium and iridium. The reason for this is obvious, looking at their relative abundance. Iron stands out as the most abundant transition metal on earth, and is positioned right above ruthenium in the periodic table.
The aim of this thesis has been to design and synthesise new photoactive iron complexes, and to apply these in artificial photosynthesis and photoredox catalysis. The strategy for both the new complexes and existing complexes has been to use N-heterocyclic carbenes (NHC) as strongly σ-donating ligands, to increase the ligand field splitting. This raises the metal-centred (MC) excited states in energy compared to the charge transfer excited states, which introduces a barrier for the deexcitation through the MC states.
In the first manuscript, a π-extended NHC ligand was used to both raise the MC state energy and lower the charge transfer state energy. The aim was to increase the barrier for deexcitation through the MC states even more. However, the ligand-to-metal charge transfer (LMCT) state of the FeIII complex was found to have a lifetime of only 14 ps, possibly because of fast direct deactivation to the ground state. The same complex was also isolated in its FeII state, which was found to have an excited state lifetime of 120 ns. The nature and potential applications of this excited state are currently investigated.
In the second chapter, the investigation of two different oxidation states of a cyclometallated iron complex, previously published in the FeIII state, revealed insights into the photophysics. While the FeIII complex had been claimed to feature dual luminescence, it was discovered that the blue emission originated from a small but highly emissive impurity.
The two final papers included in this thesis showcase the use of iron N-heterocyclic carbene complexes as photosensitisers in artificial photosynthesis and photoredox catalysis. For the first time, a high yielding hydrogen evolution reaction driven by an iron photosensitiser was demonstrated. In the photoredox catalysis reaction, an unusual biphotonic consecutive photoinduced electron transfer mechanism was found to be operating.
These findings underscore the potential of iron N-heterocyclic carbene complexes as viable and cost-effective alternatives to noble metals in photochemical applications. The research advances our understanding of iron complex photophysics and lays the groundwork for their future use in artificial photosynthesis and photoredox catalysis. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/3d8bf3c2-e030-42ec-bdaf-d9118858b2a9
- author
- Schwarz, Jesper LU
- supervisor
- opponent
-
- Professor Herbert, David, University of Manitoba, Kanada.
- organization
- publishing date
- 2024-10-29
- type
- Thesis
- publication status
- published
- subject
- keywords
- iron, N-heterocyclic carbene (NHC), Iron complexes, photocatalysis, photoredox catalysis, artificial photosynthesis, photosensitiser
- pages
- 218 pages
- publisher
- Lund University
- defense location
- KC:A
- defense date
- 2024-11-22 09:00:00
- ISBN
- 978-91-8096-069-4
- 978-91-8096-068-7
- language
- English
- LU publication?
- yes
- id
- 3d8bf3c2-e030-42ec-bdaf-d9118858b2a9
- date added to LUP
- 2024-10-28 10:16:16
- date last changed
- 2025-04-04 15:00:03
@phdthesis{3d8bf3c2-e030-42ec-bdaf-d9118858b2a9,
abstract = {{Recent years have seen a surge to develop first-row transition metal complexes with photophysics and photochemistry similar to those of noble metals, such as ruthenium and iridium. The reason for this is obvious, looking at their relative abundance. Iron stands out as the most abundant transition metal on earth, and is positioned right above ruthenium in the periodic table.<br/>The aim of this thesis has been to design and synthesise new photoactive iron complexes, and to apply these in artificial photosynthesis and photoredox catalysis. The strategy for both the new complexes and existing complexes has been to use <i>N</i>-heterocyclic carbenes (NHC) as strongly σ-donating ligands, to increase the ligand field splitting. This raises the metal-centred (MC) excited states in energy compared to the charge transfer excited states, which introduces a barrier for the deexcitation through the MC states.<br/>In the first manuscript, a π-extended NHC ligand was used to both raise the MC state energy and lower the charge transfer state energy. The aim was to increase the barrier for deexcitation through the MC states even more. However, the ligand-to-metal charge transfer (LMCT) state of the Fe<sup>III</sup> complex was found to have a lifetime of only 14 ps, possibly because of fast direct deactivation to the ground state. The same complex was also isolated in its Fe<sup>II</sup> state, which was found to have an excited state lifetime of 120 ns. The nature and potential applications of this excited state are currently investigated.<br/>In the second chapter, the investigation of two different oxidation states of a cyclometallated iron complex, previously published in the Fe<sup>III</sup> state, revealed insights into the photophysics. While the Fe<sup>III</sup> complex had been claimed to feature dual luminescence, it was discovered that the blue emission originated from a small but highly emissive impurity. <br/>The two final papers included in this thesis showcase the use of iron <i>N</i>-heterocyclic carbene complexes as photosensitisers in artificial photosynthesis and photoredox catalysis. For the first time, a high yielding hydrogen evolution reaction driven by an iron photosensitiser was demonstrated. In the photoredox catalysis reaction, an unusual biphotonic consecutive photoinduced electron transfer mechanism was found to be operating. <br/>These findings underscore the potential of iron <i>N</i>-heterocyclic carbene complexes as viable and cost-effective alternatives to noble metals in photochemical applications. The research advances our understanding of iron complex photophysics and lays the groundwork for their future use in artificial photosynthesis and photoredox catalysis.}},
author = {{Schwarz, Jesper}},
isbn = {{978-91-8096-069-4}},
keywords = {{iron; N-heterocyclic carbene (NHC); Iron complexes; photocatalysis; photoredox catalysis; artificial photosynthesis; photosensitiser}},
language = {{eng}},
month = {{10}},
publisher = {{Lund University}},
school = {{Lund University}},
title = {{Photoactive Iron N-Heterocyclic Carbene Complexes : From Design to Photoredox Catalysis}},
url = {{https://lup.lub.lu.se/search/files/198456007/Jesper_Schwarz_Thesis.pdf}},
year = {{2024}},
}