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Luminescence properties of flexible conjugated dyes
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this licentiate thesis the luminescence properties of two flexible conjugated dyes have been studied. The first, Pt1, is a platinum(II) acetylide chromophore used in optical power limiting materials. The second is a set of optical probes known as luminescent conjugated oligothiophenes (LCOs), which are used to detect and characterize the protein structures associated with amyloid diseases such as Alzheimer’s disease.

MM3 and CHARMM force field parameters have been derived for the Pt1 chromophore and LCOs, respectively, based on potential energy surface references calculated at the density functional theory (DFT)/B3LYP level of theory. The parameters have been used to perform room temperature molecular dynamics simulations of the chromophores in solvent, where tetrahydrofuran was used for Pt1 and water for the LCOs. Conformationally averaged absorption spectra were obtained, based on response theory calculations at the time-dependent DFT(TDDFT)/CAM-B3LYP level of theory for a selection of structures from the simulations. For one of the LCOs, p-HTAA, force field parameters were also created describing the dominant first excited state, based on TDDFT/B3LYP reference potential energy surfaces. These were used for molecular dynamics simulations of the chromophore in the excited state, allowing the creation of an emission spectrum. A theoretically obtained Stokes shift of 112 nm could be computed based on the absorption and emission spectra, which is in good agreement with the experimental value of 124 nm.

In addition, a quantum mechanics/molecular mechanics study of the effects of solvation on the absorption properties of the p-HTAA chromophore in water has been conducted, resulting in two models for including these effects in the averaged spectra. The first includes explicit water molecules in the form of point charges and polarizable dipole moments, and results in an absorption wavelength that is blueshifted by 2 nm from a high quality reference calculation. The second model involves the complete removal of the solvent as well as the ionic groups of the chromophore. The resulting absorption wavelength is blueshifted by an additional 4 nm as compared to the first model, but requires only one fifth of the computational resources.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 50 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1522
Keyword [en]
force field, molecular dynamics, linear absorption, QM/MM, absorption spectrum, emission spectrum, water solvation, stokes shift
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:liu:diva-75191Local ID: LIU-TEK-LIC-2012:7ISBN: 978-91-7519-948-1 (print)OAI: oai:DiVA.org:liu-75191DiVA: diva2:506103
Presentation
2012-03-28, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 621-2010-5014
Available from: 2012-03-06 Created: 2012-02-20 Last updated: 2012-03-06Bibliographically approved
List of papers
1. Platinum(II) and Phosphorus MM3 Force Field Parametrization for Chromophore Absorption Spectra at Room Temperature
Open this publication in new window or tab >>Platinum(II) and Phosphorus MM3 Force Field Parametrization for Chromophore Absorption Spectra at Room Temperature
2010 (English)In: JOURNAL OF PHYSICAL CHEMISTRY A, ISSN 1089-5639, Vol. 114, no 14, 4981-4987 p.Article in journal (Refereed) Published
Abstract [en]

Platinum(II) and phosphine MM3 force field parameters are derived from fits to the ground state potential energy surface at the level of Kohn-Sham density functional theory with employment of the B3LYP exchange-correlation functional. The parametrization includes bond stretch, angle bend, and torsional parameters for a planar platinum(II) center with phosphine and ethynyl ligands. The force field is used to study the dynamics of a fifth-generation dendrimer-coated platinum(II)organic compound in tetrahydrofurane solution at room temperature, and, based on a selection of conformations from the molecular dynamics simulation, the averaged linear absorption spectrum is determined with use of the CAM-B3LYP functional. The main absorption peak in the theoretical absorption spectrum is found at a transition wavelength of 325 nm with a full-width at half-maximum of 26 am clue to conformational broadening.

Place, publisher, year, edition, pages
American Chemical Society, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-55051 (URN)10.1021/jp911046u (DOI)000276341300039 ()
Available from: 2010-04-28 Created: 2010-04-28 Last updated: 2014-08-28
2. Molecular dynamics effects on luminescence properties of oligothiophene derivatives: a molecular mechanics-response theory study based on the CHARMM force field and density functional theory
Open this publication in new window or tab >>Molecular dynamics effects on luminescence properties of oligothiophene derivatives: a molecular mechanics-response theory study based on the CHARMM force field and density functional theory
2011 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 39, 17532-17542 p.Article in journal (Refereed) Published
Abstract [en]

CHARMM force field parameter values for a class of oligothiophene derivatives have been derived with reference to density functional theory/B3LYP potential energy surfaces. The force field parametrization of these luminescent conjugated polyelectrolytes includes the electronic ground state as well as the strongly light absorbing first excited state. In conjunction with quantum chemical response theory calculations of transition state properties, a molecular dynamical model of the Stokes shift is obtained. The theoretical model is benchmarked against experimental data recorded at room temperature which refer to sodium salts of p-HTAA and p-FTAA with distilled water as a solvent. For p-HTAA the theoretically predicted Stokes shift of 112 nm is in good agreement with the experimental result of 124 nm, given the approximations about exciton localization that were introduced to obtain a force field for the excited state.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-71564 (URN)10.1039/c1cp21252d (DOI)000295377700012 ()
Note
Funding Agencies|Swedish Research Council|621-2010-5014 |National Supercomputer Centre (NSC), Sweden||Swedish e-Science Research Center||Available from: 2011-10-21 Created: 2011-10-21 Last updated: 2017-12-08

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Sjöqvist, Jonas

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