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Molecular Trees for Collecting Sunshine -Monitoring and Controlling Energy Transfer in Dendrimers

Larsen, Jane LU (2007)
Abstract (Swedish)
Popular Abstract in Swedish

Ett ökade förbrukningen av fossila bränslen kommer att accelerera den globala uppvärmningen med oöverskådlig inverkan på oss och vår miljö. Utvecklingen av alternativa, förnybara och miljömässigt rena energiformer är därför helt essentiell. En möjlig lösning är att skapa artificiell fotosyntes, där solenergi omvandlas till bränsle (till exempel vätgas) i en process där man spjälkar vattenmolekyler. Men för att spjälka vattenmolekyler krävs det att man först infångar en stor mängd solenergi.



Denna avhandling fokuserar på undersökningar av två typer av ljusabsorberande antennsystem; (1) Zn- och Cu-porfyrin-dendrimerer med alla kromoforerna placerat i perifirin, och (2) Os-Ru... (More)
Popular Abstract in Swedish

Ett ökade förbrukningen av fossila bränslen kommer att accelerera den globala uppvärmningen med oöverskådlig inverkan på oss och vår miljö. Utvecklingen av alternativa, förnybara och miljömässigt rena energiformer är därför helt essentiell. En möjlig lösning är att skapa artificiell fotosyntes, där solenergi omvandlas till bränsle (till exempel vätgas) i en process där man spjälkar vattenmolekyler. Men för att spjälka vattenmolekyler krävs det att man först infångar en stor mängd solenergi.



Denna avhandling fokuserar på undersökningar av två typer av ljusabsorberande antennsystem; (1) Zn- och Cu-porfyrin-dendrimerer med alla kromoforerna placerat i perifirin, och (2) Os-Ru övergångsmetallkomplex med sex extra organiska pyren ligander. Effektiv energiöverföring inom dendrimererna är essentiell för att de ska kunna fungera som antenner i en solcell. Ett antal ultrasnabba tidsupplösta spektroskopiska teknikkar har använts för att studera energiöverföringen i dessa komplex med en tidsupplösning bättre än en pikosekund.



Energiöverföringsdynamiken i porfyrin dendrimererna studeras for det mesta via intensitetsberoendet av den transienta absorptionen (exciton-exciton annihilation). Denna studie visar hur energiöverföring inom dendrimererna kan optimeras och kontrolleras via små externa och/eller interna förändringar. I Zn-dendrimerarne sker energiöverföringen mellan två singlet tillstånd. Om den centrala Zn atomen ersätts med Cu dominerar tripplett tillstånden och den kombinerade Zn- / Cu-dendrimerna studien ger således en komplementärt bild av karakteristisk energiöverföringsdynamik för olika spinntillstånd.



Övergångsmetallkompleksen uppvisade snabb och effektiv energiöverföring mot det centrala Os-centret oberoende av vilken molekylär övergång som var initialt exciterad. Den primära vinsten med att addera de extra liganderna visade sig vara en kraftig förbättring av förmågan att absorbera ljus i det ultravioletta och synliga området utan att påverka den effektiva energiöverföringen till Os-centret. (Less)
Abstract
A continuing use of fossil fuels will accelerate global warning and result in severe consequences for the environment and thereby also us. Development of alternative, sustainable and environmentally friendly energy sources is therefore crucial. One approach is to create an artificial photosynthetic system that converts sunshine into fuel (e.g. hydrogen gas) by splitting water molecules. However, in order to split water molecules, a substantial amount of sunshine needs to be harvested.



This Thesis focuses on the study of two types of light-harvesting antenna systems; (1) Zn and Cu-porphyrin-appended dendrimers, where all the chromophores are situated on the periphery, and (2) a Os-Ru transition metal complex with six... (More)
A continuing use of fossil fuels will accelerate global warning and result in severe consequences for the environment and thereby also us. Development of alternative, sustainable and environmentally friendly energy sources is therefore crucial. One approach is to create an artificial photosynthetic system that converts sunshine into fuel (e.g. hydrogen gas) by splitting water molecules. However, in order to split water molecules, a substantial amount of sunshine needs to be harvested.



This Thesis focuses on the study of two types of light-harvesting antenna systems; (1) Zn and Cu-porphyrin-appended dendrimers, where all the chromophores are situated on the periphery, and (2) a Os-Ru transition metal complex with six additional organic pyrene ligands. Efficient energy transfer within the dendrimers is essential if they are to be implemented as antennas in an artificial photosynthetic device. To facilitate monitoring of the energy transfer dynamics, different ultrafast time-resolved spectroscopic techniques were employed, which enabled us to observe these dynamics on a sub-picosecond timescale.



The energy transfer dynamics in the porphyrin-appended dendrimers were mainly monitored with excitation intensity dependent transient absorption spectroscopy (exciton-exciton annihilation). The study of the Zn-dendrimer demonstrates how the energy transfer efficiency can be greatly optimized and controlled by minor external and/or internal modifications. In the Zn-dendrimers the energy transfer involves singlet excited states. However, when replacing the Zn metal center by Cu, triplet excited states are instead dominant. The combined study of Cu-porphyrin-dendrimers therefore gives a good complementary picture of the energy transfer dynamics associated with the different spin states.



The transition metal complex displays fast and efficient energy transfer towards the Os center independently of which molecular transition is excited initially. Attaching the pyrene ligands extends the light-harvesting properties both in the ultra-violet and the visible spectral region. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof. van Grondelle, Rienk, Vrije Universiteit Amsterdam, The Netherlands
organization
publishing date
type
Thesis
publication status
published
subject
keywords
magnetiska och optiska), supraledare, magnetisk resonans, egenskaper (elektriska, Kondenserade materiens egenskaper:elektronstruktur, supraconductors, magnetic resonance, relaxation, spectroscopy, Condensed matter:electronic structure, electrical, magnetic and optical properties, Kemi, Chemistry, Femtosecond transient absorption, Os-Ru metal ligand complexes, Cu-porphyrin-appended dendrimers, Zn-porphyrin-appended dendrimers, Annihilation, Energy transfer, Solar energy conversion, Artificial photosynthesis, Antenna systems, spektroskopi, Physical chemistry, Fysikalisk kemi, Photochemistry, Fotokemi, Femtosecond fluorescence anisotropy
pages
160 pages
publisher
Department of Chemical Physics, Lund University
defense location
Hall B Chemical Center Lund University
defense date
2007-02-02 13:15
ISBN
91-7422-136-1 / 978-91-7422-136-7
language
English
LU publication?
yes
id
3a65d47b-6a17-49ab-bea7-71f9436f2ef4 (old id 547859)
date added to LUP
2007-10-09 12:32:10
date last changed
2016-09-19 08:45:10
@misc{3a65d47b-6a17-49ab-bea7-71f9436f2ef4,
  abstract     = {A continuing use of fossil fuels will accelerate global warning and result in severe consequences for the environment and thereby also us. Development of alternative, sustainable and environmentally friendly energy sources is therefore crucial. One approach is to create an artificial photosynthetic system that converts sunshine into fuel (e.g. hydrogen gas) by splitting water molecules. However, in order to split water molecules, a substantial amount of sunshine needs to be harvested.<br/><br>
<br/><br>
This Thesis focuses on the study of two types of light-harvesting antenna systems; (1) Zn and Cu-porphyrin-appended dendrimers, where all the chromophores are situated on the periphery, and (2) a Os-Ru transition metal complex with six additional organic pyrene ligands. Efficient energy transfer within the dendrimers is essential if they are to be implemented as antennas in an artificial photosynthetic device. To facilitate monitoring of the energy transfer dynamics, different ultrafast time-resolved spectroscopic techniques were employed, which enabled us to observe these dynamics on a sub-picosecond timescale.<br/><br>
<br/><br>
The energy transfer dynamics in the porphyrin-appended dendrimers were mainly monitored with excitation intensity dependent transient absorption spectroscopy (exciton-exciton annihilation). The study of the Zn-dendrimer demonstrates how the energy transfer efficiency can be greatly optimized and controlled by minor external and/or internal modifications. In the Zn-dendrimers the energy transfer involves singlet excited states. However, when replacing the Zn metal center by Cu, triplet excited states are instead dominant. The combined study of Cu-porphyrin-dendrimers therefore gives a good complementary picture of the energy transfer dynamics associated with the different spin states.<br/><br>
<br/><br>
The transition metal complex displays fast and efficient energy transfer towards the Os center independently of which molecular transition is excited initially. Attaching the pyrene ligands extends the light-harvesting properties both in the ultra-violet and the visible spectral region.},
  author       = {Larsen, Jane},
  isbn         = {91-7422-136-1 / 978-91-7422-136-7},
  keyword      = {magnetiska och optiska),supraledare,magnetisk resonans,egenskaper (elektriska,Kondenserade materiens egenskaper:elektronstruktur,supraconductors,magnetic resonance,relaxation,spectroscopy,Condensed matter:electronic structure,electrical,magnetic and optical properties,Kemi,Chemistry,Femtosecond transient absorption,Os-Ru metal ligand complexes,Cu-porphyrin-appended dendrimers,Zn-porphyrin-appended dendrimers,Annihilation,Energy transfer,Solar energy conversion,Artificial photosynthesis,Antenna systems,spektroskopi,Physical chemistry,Fysikalisk kemi,Photochemistry,Fotokemi,Femtosecond fluorescence anisotropy},
  language     = {eng},
  pages        = {160},
  publisher    = {ARRAY(0x6a3aa50)},
  title        = {Molecular Trees for Collecting Sunshine -Monitoring and Controlling Energy Transfer in Dendrimers},
  year         = {2007},
}