Life of Excitons in Artificial Photosynthetic Antennas
(2005)- Abstract
- Due to the predicted energy crisis when fossil fuels will be exhausted it is important to search for alternative energy sources. Utilizing sunlight via artificial photosynthesis is an interesting possibility. The long-term goal for research in this area is to design and build molecular and/or solid state systems that can use sunlight to split water and produce fuel (e.g. hydrogen). Nature tells us that such a system should consist of a light-harvesting antenna coupled to the photochemical reaction center, for highest efficiency.
In this Thesis both reaction center and antenna functions are studied, with the emphasis on artificial antennas. We have studied two types of antennas, dendrimers of transition metal polypyridine... (More) - Due to the predicted energy crisis when fossil fuels will be exhausted it is important to search for alternative energy sources. Utilizing sunlight via artificial photosynthesis is an interesting possibility. The long-term goal for research in this area is to design and build molecular and/or solid state systems that can use sunlight to split water and produce fuel (e.g. hydrogen). Nature tells us that such a system should consist of a light-harvesting antenna coupled to the photochemical reaction center, for highest efficiency.
In this Thesis both reaction center and antenna functions are studied, with the emphasis on artificial antennas. We have studied two types of antennas, dendrimers of transition metal polypyridine complexes and Zn-porphyrin dendrimers. In order to study the ultrafast energy transfer and relaxation processes in these molecules we have employed polarization sensitive time resolved absorption and fluorescence spectroscopy.
In the study of transition metal dendrimers we used very short, ~30 fs, laser pulses to elucidate the processes involved in energy migration within a tetramer transition metal complex, Os{(µ-2,3-dpp (Ru(bpy)2)3}8+. This complex is funneling all deposited photon energy to the central Os core. From our experiments we can identify two pathways of energy transfer from the Ru-moieties to the Os-core, a singlet pathway characterized by a time constant of < 60 fs and a more than ten times slower triplet pathway. Experiments on monomeric building blocks were important in order to obtain a complete picture of the processes in the denrimers, and showed that excited state localization occurs in < 50 fs, intersystem crossing in the Ru-complexes takes ~80 fs, but is faster (< 50 fs) in the Os-complexes. Thermally activated interligand electron transfer occurs with a characteristic time of ~10 ps in complexes with equivalent ligands; in complexes with dissimilar ligands the excitation is trapped on the lowest energy ligand.
Zn-porphyrin dendrimers of various sizes (4-64 chromophores) and the monomeric Zn-porphyrin building block were studied by a fluorescence streak-camera. Energy transfer of Förster type between the four nearest neighboring Zn- porphyrins within a dendron was observed. Transfer time is on a timescale of 100 ps at 200 K. The fact that energy transfer only occur over four chromophores, even in the largest molecule of 64 Zn-porphyrins, shows that the structure of the dendrimer has to be optimized to obtain an efficient light-harvesting and transporting system. (Less) - Abstract (Swedish)
- Popular Abstract in Swedish
På grund av den förutspådda energi krisen som föranleds av att oljan tar slut, är det viktigt att söka efter alternativa energikällor. Att utnyttja solljuset via en artificiell fotosyntes är en intressant möjlighet. Det långsiktiga målet för forskning på detta område är att bygga molekylära och/eller fasta material som kan använda solljus för att dela vatten i dess beståndsdelar. På så sätt kan bränsle i form av väte utvinnas. Naturen visar oss att ett sådant system borde innehålla ett ljusinsamlande antennsystem kopplat till ett reaktionscenter, för bästa effektivitet.
I denna avhandling har vi studerat både reaktionscenter och antennfunktioner, med tyngdpunkt på artificiella... (More) - Popular Abstract in Swedish
På grund av den förutspådda energi krisen som föranleds av att oljan tar slut, är det viktigt att söka efter alternativa energikällor. Att utnyttja solljuset via en artificiell fotosyntes är en intressant möjlighet. Det långsiktiga målet för forskning på detta område är att bygga molekylära och/eller fasta material som kan använda solljus för att dela vatten i dess beståndsdelar. På så sätt kan bränsle i form av väte utvinnas. Naturen visar oss att ett sådant system borde innehålla ett ljusinsamlande antennsystem kopplat till ett reaktionscenter, för bästa effektivitet.
I denna avhandling har vi studerat både reaktionscenter och antennfunktioner, med tyngdpunkt på artificiella antenner. Vi har studerat två typer av antenner, övergångsmetall pollypyridin dendrimerer och Zn-porfyrin dendrimerer. För att studera de ultrasnabba energiöverföringsprocesserna har vi använt oss av polarisations känslig tidsupplöst absorption och fluorescens spektroskopi. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/545125
- author
- Andersson, Johan LU
- supervisor
- opponent
-
- Professor Vlcek, Antonin, Department of Chemistry, Queen Mary University of London
- organization
- publishing date
- 2005
- type
- Thesis
- publication status
- published
- subject
- keywords
- Zn-porphyrin, Osmium, Ruthenium, Polypyridine, Inter Ligand Energy Transfer, Inter System Crossing, Excited state dynamics, Transition metal complexes, Photosynthetic Antennas, Solar energy conversion, Artificial photosynthesis, Physical chemistry, Fysikalisk kemi, Transient Absorption Anisotropy., Reaction Center, Dendrimer, Energy Transfer
- pages
- 116 pages
- publisher
- Chemical Physics, Lund University
- defense location
- Sal F Kemicentrum, Lunds universitet Getingevägen 60, Lund
- defense date
- 2005-06-17 13:15:00
- ISBN
- 91-7422-087-X
- language
- English
- LU publication?
- yes
- additional info
- The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Chemical Physics (S) (011001060)
- id
- 3a5be009-4fbe-4ea9-9929-cbf7b7b74230 (old id 545125)
- date added to LUP
- 2016-04-04 11:31:43
- date last changed
- 2018-11-21 21:05:26
@phdthesis{3a5be009-4fbe-4ea9-9929-cbf7b7b74230,
abstract = {{Due to the predicted energy crisis when fossil fuels will be exhausted it is important to search for alternative energy sources. Utilizing sunlight via artificial photosynthesis is an interesting possibility. The long-term goal for research in this area is to design and build molecular and/or solid state systems that can use sunlight to split water and produce fuel (e.g. hydrogen). Nature tells us that such a system should consist of a light-harvesting antenna coupled to the photochemical reaction center, for highest efficiency.<br/><br>
<br/><br>
In this Thesis both reaction center and antenna functions are studied, with the emphasis on artificial antennas. We have studied two types of antennas, dendrimers of transition metal polypyridine complexes and Zn-porphyrin dendrimers. In order to study the ultrafast energy transfer and relaxation processes in these molecules we have employed polarization sensitive time resolved absorption and fluorescence spectroscopy.<br/><br>
<br/><br>
In the study of transition metal dendrimers we used very short, ~30 fs, laser pulses to elucidate the processes involved in energy migration within a tetramer transition metal complex, Os{(µ-2,3-dpp (Ru(bpy)2)3}8+. This complex is funneling all deposited photon energy to the central Os core. From our experiments we can identify two pathways of energy transfer from the Ru-moieties to the Os-core, a singlet pathway characterized by a time constant of < 60 fs and a more than ten times slower triplet pathway. Experiments on monomeric building blocks were important in order to obtain a complete picture of the processes in the denrimers, and showed that excited state localization occurs in < 50 fs, intersystem crossing in the Ru-complexes takes ~80 fs, but is faster (< 50 fs) in the Os-complexes. Thermally activated interligand electron transfer occurs with a characteristic time of ~10 ps in complexes with equivalent ligands; in complexes with dissimilar ligands the excitation is trapped on the lowest energy ligand.<br/><br>
<br/><br>
Zn-porphyrin dendrimers of various sizes (4-64 chromophores) and the monomeric Zn-porphyrin building block were studied by a fluorescence streak-camera. Energy transfer of Förster type between the four nearest neighboring Zn- porphyrins within a dendron was observed. Transfer time is on a timescale of 100 ps at 200 K. The fact that energy transfer only occur over four chromophores, even in the largest molecule of 64 Zn-porphyrins, shows that the structure of the dendrimer has to be optimized to obtain an efficient light-harvesting and transporting system.}},
author = {{Andersson, Johan}},
isbn = {{91-7422-087-X}},
keywords = {{Zn-porphyrin; Osmium; Ruthenium; Polypyridine; Inter Ligand Energy Transfer; Inter System Crossing; Excited state dynamics; Transition metal complexes; Photosynthetic Antennas; Solar energy conversion; Artificial photosynthesis; Physical chemistry; Fysikalisk kemi; Transient Absorption Anisotropy.; Reaction Center; Dendrimer; Energy Transfer}},
language = {{eng}},
publisher = {{Chemical Physics, Lund University}},
school = {{Lund University}},
title = {{Life of Excitons in Artificial Photosynthetic Antennas}},
year = {{2005}},
}