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Quantum Chemical Modeling of Dye-Sensitized Titanium Dioxide: Ruthenium Polypyridyl and Perylene Dyes, TiO2 Nanoparticles, and Their Interfaces
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quantum chemical calculations have been used to model dye-sensitized nanostructured titanium dioxide systems that can be used in solar cells for solar energy to electricity conversion. Structural, electronic and spectral properties of isolated dyes and both bare and dye-sensitized TiO2 have been calculated with density functional theory, providing detailed information about both the separate parts and the dye-TiO2 interface.

The connection between the geometry, the ligand field splitting and the lifetime of the triplet metal-to-ligand charge transfer (MLCT) excited state has been explored for a series of ruthenium polypyridyl dyes. Moreover, the relative energetics of MLCT and metal centered triplet excited states have been studied for a number of such systems. It was found that small alterations of the polypyridyl ligands can result in significant changes in ligand field splitting and in the energetics of the triplet states.

Attachment of the dyes to the TiO2 surface is achieved via anchor and spacer groups. The influence of such groups on various properties of the dye and their ability to act as mediators of photo-induced surface electron transfer has been studied. Delocalization of the lowest unoccupied dye orbital onto the spacer and/or anchor group indicates that certain unsaturated groups can mediate electron transfer.

With a combination of methods that enables efficient computations and a scheme for construction of metal oxide clusters, chemical models for bare TiO2 nanocrystals in the 1-2 nm size range have been developed. The electronic structures show well-developed band structures with essentially no electronic band gap defect states.

Atomistic models of the interface between TiO2 nanocrystals and Ru(II)-bis-terpyridine dyes, the so-called N3 dye as well as perylene dyes are reported. Electronic coupling strengths, which provide estimates for the electron injection times, are extracted from the interfacial electronic structure and the lowest electronic excitations are calculated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2006. , p. 68
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 220
Keywords [en]
Quantum chemistry, density functional theory, chromophore, nanocrystal, interface, photoexcitation, triplet state, surface electron transfer, electronic coupling strength
Keywords [sv]
Kvantkemi
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-7141ISBN: 91-554-6650-8 (print)OAI: oai:DiVA.org:uu-7141DiVA, id: diva2:168857
Public defence
2006-10-13, Häggsalen, Ångströmlaboratoriet, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2006-09-22 Created: 2006-09-22 Last updated: 2013-05-17Bibliographically approved
List of papers
1. Structural and Spectral Investigation of Ruthenium(II) Polypyridyl Complexes by DFT Calculations
Open this publication in new window or tab >>Structural and Spectral Investigation of Ruthenium(II) Polypyridyl Complexes by DFT Calculations
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(English)In: Inorganic ChemistryArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-95090 (URN)
Available from: 2006-11-09 Created: 2006-11-09 Last updated: 2013-05-17Bibliographically approved
2. Ruthenium complexes of bipyridyl(pyridyl)alkane ligands: Effect of methylene or iso-propylene bridge on structural and photophysical properties
Open this publication in new window or tab >>Ruthenium complexes of bipyridyl(pyridyl)alkane ligands: Effect of methylene or iso-propylene bridge on structural and photophysical properties
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(English)Manuscript (Other (popular science, discussion, etc.))
Identifiers
urn:nbn:se:uu:diva-94851 (URN)
Available from: 2006-09-22 Created: 2006-09-22 Last updated: 2011-03-21
3. Calculated optoelectronic properties of Ruthenium tris-bipyridine dyes containing oligophenyleneethynylene rigid rod linkers in different chemical environments
Open this publication in new window or tab >>Calculated optoelectronic properties of Ruthenium tris-bipyridine dyes containing oligophenyleneethynylene rigid rod linkers in different chemical environments
2007 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 111, no 8, p. 1487-1497Article in journal (Refereed) Published
Abstract [en]

Ruthenium tris-bipyridine dyes containing oligophenyleneethynylene (OPE) rigid rod linker groups ([Ru(bpy)3]2+, [Ru(bpy)2bpy-E-Ipa]2+, [Ru(bpy)2bpy-E-Ph-E-Ipa]2+, and [Ru(bpy)2bpy-E-Bco-E-Ipa]2+, where bpy = 2,2'-bipyridine, E = ethynylene, Ph = p-phenylene, Bco = bicyclo[2.2.2]octylene, and Ipa = isophthalic acid) have been investigated using DFT and TD-DFT calculations to elucidate the influence of the rigid rod on their optoelectronic properties. Experimentally observed differences in the optical absorption for the different complexes are discussed on the basis of TD-DFT simulated absorption spectra. A comparison of the calculated optoelectronic properties of [Ru(bpy)2bpy-E-Ph-E-Ipa]2+ in different chemical environments, that is, in different solvents and with or without counter ions, suggests that both the absorption spectra and the redox properties of the dyes with OPE rods are sensitive to the environment. The calculations show that spurious low-energy charge-transfer excitations present in the TD-DFT calculations of the extended systems in vacuum are removed when the environment is included in the calculations.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-94852 (URN)10.1021/jp064219x (DOI)000244348100013 ()17279731 (PubMedID)
Available from: 2006-09-22 Created: 2006-09-22 Last updated: 2017-12-14Bibliographically approved
4. Spacer and anchor effects on the electronic coupling in Ruthenium-bis-terpyridine dye-sensitized TiO2 nanocrystals studied by DFT
Open this publication in new window or tab >>Spacer and anchor effects on the electronic coupling in Ruthenium-bis-terpyridine dye-sensitized TiO2 nanocrystals studied by DFT
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2006 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 41, p. 20513-20525Article in journal (Refereed) Published
Abstract [en]

Structural and electronic properties of TiO2 nanoparticles sensitized with a set of Ru(II)(tpy)2 based dyes have been investigated using density functional theory (DFT) calculations combined with time-dependent (TD) DFT calculations. The effects of carboxylic and phosphonic acid anchor groups, as well as a phenylene spacer group, on the optical properties of the dyes and the electronic interactions in the dye-sensitized TiO2 nanoparticles have been investigated. Inclusion of explicit counterions in the modeling shows that the description of the environment is important in order to obtain a realistic interfacial energy level alignment. A comparison of calculated electronic coupling strengths suggests that both the nature of the anchor group and the inclusion of the phenylene spacer group are capable of significantly influencing electron-transfer rates across the dye-metal oxide interface.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-94853 (URN)10.1021/jp064045j (DOI)000241192200066 ()17034238 (PubMedID)
Available from: 2006-09-22 Created: 2006-09-22 Last updated: 2017-12-14Bibliographically approved
5. DFT study of bare and dye-sensitized TiO2 clusters and nanocrystals
Open this publication in new window or tab >>DFT study of bare and dye-sensitized TiO2 clusters and nanocrystals
2006 (English)In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 106, no 15, p. 3214-3234Article in journal (Refereed) Published
Abstract [en]

Structural and electronic properties of bare and dye-sensitized TiO2 clusters and nanoparticles with sizes of ?2 nm have been studied by density functional theory (DFT) calculations. Starting from truncated bulk lattice structures, the degree of structural reorganization, including the formation of Ti dbond O surface species, of bare TiO2 anatase nanocrystals, is found to be sensitive to the quality of the computational method. The electronic structures of optimized 1-2 nm nanoparticles show well-developed band structures with essentially no electronic bandgap defect states. Significant bandgap broadening due to quantum size effects is observed as the size of the nanocrystals is reduced from 2 nm to 1 nm in diameter, but further bandgap widening is limited by increasingly severe competing surface defect sites as the particles become smaller than ?1 nm in diameter. The applicability of the TiO2 nanocrystals in modeling the electronic structure and electronic coupling at dye-sensitized TiO2 nanocrystal interfaces has been investigated by attachment of pyridine to one of the nanoparticle models via phosphonic or carboxylic acid anchor groups.

Keywords
DFT, TiO2, cluster, nanocrystal, surface electron transfer
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-94854 (URN)10.1002/qua.21088 (DOI)
Available from: 2006-09-22 Created: 2006-09-22 Last updated: 2017-12-14Bibliographically approved
6. Quantum chemical calculations of the influence of anchor-cum-spacer groups on femtosecond electron transfer times in dye-sensitized semiconductor nanocrystals
Open this publication in new window or tab >>Quantum chemical calculations of the influence of anchor-cum-spacer groups on femtosecond electron transfer times in dye-sensitized semiconductor nanocrystals
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2006 (English)In: Journal of Chemical Theory and Computation, Vol. 2, no 2, p. 441-451Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-94855 (URN)
Available from: 2006-09-22 Created: 2006-09-22 Last updated: 2009-03-26Bibliographically approved
7. Calculated structural and electronic interactions of the Ruthenium dye N3 with a titanium dioxide nanocrystal
Open this publication in new window or tab >>Calculated structural and electronic interactions of the Ruthenium dye N3 with a titanium dioxide nanocrystal
2005 (English)In: Journal of Physical Chemistry B, Vol. 109, no 24, p. 11918-11924Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-94856 (URN)
Available from: 2006-09-22 Created: 2006-09-22 Last updated: 2009-03-26Bibliographically approved

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