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A combined MD/QM and experimental exploration of conformational richness in branched oligothiophenes
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
University of Málaga, Spain.
University of Málaga, Spain.
University of Málaga, Spain.
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2014 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 45, 24841-24852 p.Article in journal (Refereed) Published
Abstract [en]

Infrared (IR) absorption and vibrational Raman spectra of a family of branched oligothiophenes have been determined experimentally as well as theoretically. The molecular spectra have been compared to those of the linear analogues, with identification made of spectral features due to structural properties that are valued in organic solar cell applications. The theoretical spectra have been obtained through a newly developed method in which individual conformer spectra, calculated at the time-dependent DFT level in this work, are weighted by statistics extracted from classical molecular dynamics trajectories. The agreement with experiment for the resulting averaged spectra is at least as good as, and often better than, what is observed for Boltzmann-weighted spectra. As the weights are available before the costly step of spectrum calculation, the method has the additional advantage of enabling efficient approximations. For simulating the molecular dynamics of the studied α,β-linked thiophenes and 2-methylthiophenes, high quality parameters have been derived for the CHARMM force field. Furthermore, the temperature dependence of the IR and Raman spectra have been investigated, both experimentally and theoretically.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2014. Vol. 16, no 45, 24841-24852 p.
Keyword [en]
organic solar cells, time-dependent density functional theory, CHARMM, IR spectroscopy, Raman spectroscopy
National Category
Theoretical Chemistry Organic Chemistry
URN: urn:nbn:se:liu:diva-109096DOI: 10.1039/c4cp03365eISI: 000344464800023PubMedID: 25319050OAI: diva2:737014
Available from: 2014-08-11 Created: 2014-08-07 Last updated: 2015-02-17Bibliographically approved
In thesis
1. Light interactions in flexible conjugated dyes
Open this publication in new window or tab >>Light interactions in flexible conjugated dyes
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis methodological developments have been made for the description of flexible conjugated dyes in room temperature spectrum calculations.

The methods in question target increased accuracy and efficiency by combining classical molecular dynamics (MD) simulations with time-dependent response theory spectrum calculations. For absorption and fluorescence spectroscopies a form of conformational averaging is used, where the final spectrum is obtained as an average of spectra calculated for geometries extracted from ground and excited state MD simulations. For infrared and Raman spectroscopies averaged spectra are calculated based on individual spectra, obtained for zero-temperature optimized molecular structures, weighted by conformational statistics from MD trajectories. Statistics for structural properties are also used in both cases to gain additional information about the systems, allowing more efficient utilization of computational resources. As it is essential that the molecular mechanics description of the system is highly accurate for methods of this nature to be effective, high quality force field parameters have been derived, describing the molecules of interest in either the MM3 or CHARMM force fields.

These methods have been employed in the study of three systems. The first is a platinum(II) actylide chromophore used in optical power limiting materials, for which a ultraviolet/visible absorption spectrum has been calculated. The second is a family of molecular probes called luminescent conjugated oligothiophenes, used to detect and characterize amyloid proteins, for which both absorption and fluorescence spectra have been calculated. Finally, infrared and Raman spectra have been calculated for a group of branched oligothiophenes used in organic solar cells.

In addition, solvation effects have been studied for conjugated poly\-eletrolytes in water, resulting in the development of two solvation models suitable for this class of molecules. The first uses a quantum meachanics/molecular mechanics (QM/MM) description, in which the solute mole\-cule is described using accurate quantum mechanical methods while the surrounding water molecules are described using point charges and polarizable point dipoles. The second discards the water entirely and removes the ionic groups of the solute. The QM/MM model provides highly accurate results while the cut-down model gives results of slightly lower quality but at a much reduced computational cost.

Finally, a study of protein-dye interactions has been performed, with the goal of explaining changes in the luminescence properties of the LCO chromophores when in the presence of amyloid proteins. Results were less than conclusive.

Place, publisher, year, edition, pages
Linköping, Sweden: Linköping University Electronic Press, 2014. 63 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1608
force field, molecular dynamics, QM/MM, solvation effects, absorption spectroscopy, fluorescence spectrosocopy, infrared spectroscopy, Raman spectroscopy, stokes shift, conjugated polyelectrolytes
National Category
Theoretical Chemistry
urn:nbn:se:liu:diva-109011 (URN)10.3384/diss.diva-109011 (DOI)978-91-7519-282-6 (print) (ISBN)
Public defence
2014-09-12, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:00 (English)
Available from: 2014-08-28 Created: 2014-07-26 Last updated: 2014-08-28Bibliographically approved

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