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Photophysics and Photochemistry of Iron Carbene Complexes

Lindh, Linnea LU orcid (2023)
Abstract
Nature captures sunlight via light-absorbing molecules.
Similarly, photosensitisers are used in applications of solar cells and artificial photosynthesis to absorb sunlight, and transfer the excited electron.
Successful photosensitisers have in the past been based on a Ru polipyridyl scaffold, despite Ru being one of the scarcest elements in Earth's crust.
This thesis work aims to replace Ru polipyridyl complexes by Fe carbene complexes, that by clever ligand design have approached suitable photosensitiser properties.

One crucial property that is not yet competitive for Fe carbene photosensitisers is how long they stay in the excited state, i.e. their lifetime.
This is controlled by the deactivation pathways of... (More)
Nature captures sunlight via light-absorbing molecules.
Similarly, photosensitisers are used in applications of solar cells and artificial photosynthesis to absorb sunlight, and transfer the excited electron.
Successful photosensitisers have in the past been based on a Ru polipyridyl scaffold, despite Ru being one of the scarcest elements in Earth's crust.
This thesis work aims to replace Ru polipyridyl complexes by Fe carbene complexes, that by clever ligand design have approached suitable photosensitiser properties.

One crucial property that is not yet competitive for Fe carbene photosensitisers is how long they stay in the excited state, i.e. their lifetime.
This is controlled by the deactivation pathways of the molecule, dictated by the excited state landscape.
Several Fe carbene photosensitisers were in this thesis investigated by spectroscopic and computational methods, to understand their deactivation pathways.
For the Fe(II) carbene complexes investigated, small changes in the ligand structure influenced both what excited state (charge-transfer or metal-centred) that was mainly populated and the lifetime of the state.
For the Fe(III) carbene complexes investigated, there was instead one dominating charge-transfer excited state that was rather unaffected by changes to the ligand.
Furthermore, for the Fe(II) complexes metal-centred states played a large role in the deactivation pathway but for the Fe(III) complexes this was not the case.
Also, one Co(III) carbene complex was investigated which displays remarkable long lifetime and emission from a metal-centred state.

As a first step towards application, the electron-transfer properties of some of the photosensitisers were investigated.
Fe(II) complexes with a push-pull design were able to transfer electrons to TiO2 in a solar cell configuration.
The solar cell performance was however limited by an ultrafast recombination reaction, that brought a majority of the transferred electrons back to the photosensitiser.
The Fe(III) complexes investigated had long enough lifetime to participate in electron transfer with other molecules in solution, if the concentration was high.
Furthermore, at very high concentrations of the photosensitiser a light-induced charge-disproportionation reaction outcompeted all other deactivation pathways.
In a heterogeneous catalysis configuration, this reaction could generate long-lived Fe(IV) species with the correct additives.
The thesis work thus provide fundamental insights to the early implementations of Fe carbene photosensitisers in applications, by resolving key electron-transfer processes on the ultrafast timescale. (Less)
Abstract (Swedish)
I naturen fångas solljus in via ljus-absorberande molekyler.
På liknande sätt kan färgämnen användas för solcells- och artificiell fotosyntes-applikationer för att absorbera solljus, och överföra den exciterade elektronen.
Framgångsrika färgämnen har tidigare varit baserade på Ru-polipyridyl-komplex, trots att Ru är ett av de mest ovanliga ämnena i jordskorpan.
Detta arbete har som mål att ersätta Ru-komplexen med Fe-karben-komplex, vilka på senare år har uppnått goda färgämnesegenskaper genom smart ligand-design.

En strikt avgörande egenskap där Fe-karben-komplex ännu inte är konkurrenskraftiga är hur länge de stannar i det exciterade tillståndet, dvs deras livstid.
Detta styrs av de möjliga... (More)
I naturen fångas solljus in via ljus-absorberande molekyler.
På liknande sätt kan färgämnen användas för solcells- och artificiell fotosyntes-applikationer för att absorbera solljus, och överföra den exciterade elektronen.
Framgångsrika färgämnen har tidigare varit baserade på Ru-polipyridyl-komplex, trots att Ru är ett av de mest ovanliga ämnena i jordskorpan.
Detta arbete har som mål att ersätta Ru-komplexen med Fe-karben-komplex, vilka på senare år har uppnått goda färgämnesegenskaper genom smart ligand-design.

En strikt avgörande egenskap där Fe-karben-komplex ännu inte är konkurrenskraftiga är hur länge de stannar i det exciterade tillståndet, dvs deras livstid.
Detta styrs av de möjliga deaktiveringsvägarna som finns i molekylen, vilket dikteras av landskapet av exciterade tillstånd.
Flera Fe-karben-komplex har undersökts i denna avhandling genom spektroskopi och beräkningar, för att förstå deras deaktiveringsvägar.
För de undersökta Fe(II)-karben-komplexen, så influerade små ändringar i ligandstrukturen både vilket exciterat tillstånd (laddningsseparerat eller metalcentrerat) som var dominerande och dess livstid.
För de undersökta Fe(III)-karben-komplexen, så fanns det istället ett dominerande laddningsseparerat tillstånd som var relativt opåverkat av ändringar i ligandstrukturen.
För Fe(II)-komplexen var metalcentrerade tillstånd viktiga för deaktiveringsvägen, men för Fe(III)-komplexen så var detta inte en lika viktig faktor.
Även ett Co(III)-karben-komplex undersöktes i avhandlingen, och detta komplex hade ett metalcentrerat exciterat tillstånd med ovanligt lång livstid samt emission.

Som ett första steg mot applikationer, så undersöktes även elektron-överföringsförmågan för vissa av färgämnena.
Fe(II)-komplexen med en "push-pull"-design visade prov på att kunna överföra elektroner till TiO2 i en prototyp-solcell.
Solcellseffektiviteten begränsades dock av en ultrasnabb rekombinationsreaktion, vilken transporterade majoriteten av elektronerna tillbaka till färgämnet.
De undersökta Fe(III)-komplexen hade tillräckligt lång livstid för att kunna överföra laddningsbärare till andra molekyler i lösning, om koncentrationen var tillräckligt hög.
Vid väldigt hög koncentration, skedde dock en mycket effektiv ljus-inducerad laddnings-disproportionering.
I en prototyp för heterogen katalys, så kunde denna reaktion med korrekt tillsatsämnen möjliggöra Fe(IV)-specier med lång livstid.
Denna avhandling ger därför fundamentala insikter i den tidiga tillämpningen av Fe-karben-komplex i applikationer, genom att undersöka viktiga elektronöverföringsreaktioner på ultrasnabb tidsskala. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor J. Meyer, Gerald, CHASE Solar Fuels Hub University of North Carolina at Chapel Hill
organization
alternative title
Järnkarben-komplexens fotofysik och fotokemi
publishing date
type
Thesis
publication status
published
subject
keywords
tidsupplöst spektroskopi, täthetsfunktionalteori, järn-komplex, färgämne, grätzelsolcell, fotokatalys, elektronöverföringsreaktion, time-resolved spectroscopy, density functional theory, earth-abundant, iron-complex, photosensitiser, dye-sensitised solar cell, photocatalysis, electron transfer
pages
129 pages
publisher
MediaTryck Lund
defense location
Kemicentrum, KC:A. Join via zoom: https://lu-se.zoom.us/j/62615627504
defense date
2023-10-06 09:00:00
ISBN
978-91-7422-976-9
978-91-7422-977-6
project
Photophysics and Photochemistry of Iron Carbene Complexes
language
English
LU publication?
yes
id
d35a7e5f-4da1-48c9-a566-d74f2bac3430
date added to LUP
2023-09-12 11:58:15
date last changed
2024-03-26 11:39:48
@phdthesis{d35a7e5f-4da1-48c9-a566-d74f2bac3430,
  abstract     = {{Nature captures sunlight via light-absorbing molecules.<br/>Similarly, photosensitisers are used in applications of solar cells and artificial photosynthesis to absorb sunlight, and transfer the excited electron.<br/>Successful photosensitisers have in the past been based on a Ru polipyridyl scaffold, despite Ru being one of the scarcest elements in Earth's crust.<br/>This thesis work aims to replace Ru polipyridyl complexes by Fe carbene complexes, that by clever ligand design have approached suitable photosensitiser properties.<br/><br/>One crucial property that is not yet competitive for Fe carbene photosensitisers is how long they stay in the excited state, i.e. their lifetime. <br/>This is controlled by the deactivation pathways of the molecule, dictated by the excited state landscape. <br/>Several Fe carbene photosensitisers were in this thesis investigated by spectroscopic and computational methods, to understand their deactivation pathways. <br/>For the Fe(II) carbene complexes investigated, small changes in the ligand structure influenced both what excited state (charge-transfer or metal-centred) that was mainly populated and the lifetime of the state.<br/>For the Fe(III) carbene complexes investigated, there was instead one dominating charge-transfer excited state that was rather unaffected by changes to the ligand. <br/>Furthermore, for the Fe(II) complexes metal-centred states played a large role in the deactivation pathway but for the Fe(III) complexes this was not the case.<br/>Also, one Co(III) carbene complex was investigated which displays remarkable long lifetime and emission from a metal-centred state.<br/><br/>As a first step towards application, the electron-transfer properties of some of the photosensitisers were investigated.<br/>Fe(II) complexes with a push-pull design were able to transfer electrons to TiO2 in a solar cell configuration.<br/>The solar cell performance was however limited by an ultrafast recombination reaction, that brought a majority of the transferred electrons back to the photosensitiser.<br/>The Fe(III) complexes investigated had long enough lifetime to participate in electron transfer with other molecules in solution, if the concentration was high.<br/>Furthermore, at very high concentrations of the photosensitiser a light-induced charge-disproportionation reaction outcompeted all other deactivation pathways. <br/>In a heterogeneous catalysis configuration, this reaction could generate long-lived Fe(IV) species with the correct additives.<br/>The thesis work thus provide fundamental insights to the early implementations of Fe carbene photosensitisers in applications, by resolving key electron-transfer processes on the ultrafast timescale.}},
  author       = {{Lindh, Linnea}},
  isbn         = {{978-91-7422-976-9}},
  keywords     = {{tidsupplöst spektroskopi; täthetsfunktionalteori; järn-komplex; färgämne; grätzelsolcell; fotokatalys; elektronöverföringsreaktion; time-resolved spectroscopy; density functional theory; earth-abundant; iron-complex; photosensitiser; dye-sensitised solar cell; photocatalysis; electron transfer}},
  language     = {{eng}},
  publisher    = {{MediaTryck Lund}},
  school       = {{Lund University}},
  title        = {{Photophysics and Photochemistry of Iron Carbene Complexes}},
  url          = {{https://lup.lub.lu.se/search/files/158233839/Linnea_Lindh_WEBB.pdf}},
  year         = {{2023}},
}