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Assessment of a composite CC2/DFT procedure for calculating 0-€“0 excitation energies of organic molecules
Linköping University, Department of Physics, Chemistry and Biology, Bioinformatics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Bioinformatics. Linköping University, Faculty of Science & Engineering.
2016 (English)In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, 1-16 p.Article in journal (Refereed) Epub ahead of print
Abstract [en]

The task to assess the performance of quantum chemical methods in describing electronically excited states has in recent years started to shift from calculation of vertical (ΔEve) to calculation of 0-€“0 excitation energies (ΔE00). Here, based on a set of 66 excited states of organic molecules for which high-resolution experimental ΔE00 energies are available and for which the approximate coupled-cluster singles and doubles (CC2) method performs particularly well, we explore the possibility to simplify the calculation of CC2-quality ΔE00 energies using composite procedures that partly replace CC2 with more economical methods. Specifically, we consider procedures that employ CC2 only for the ΔEve part and density functional theory methods for the cumbersome excited-state geometry optimisations and frequency calculations required to obtain ΔE00 energies from ΔEve ones. The results demonstrate that it is indeed possible to both closely (to within 0.06-€“0.08 eV) and consistently approximate ‘true’ CC2 ΔE00 energies in this way, especially when CC2 is combined with hybrid density functionals. Overall, the study highlights the unexploited potential of composite procedures, which hitherto have found widespread use mostly in ground-state chemistry, to also play an important role in facilitating accurate studies of excited states.

Place, publisher, year, edition, pages
Taylor & Francis, 2016. 1-16 p.
National Category
Theoretical Chemistry Atom and Molecular Physics and Optics Chemical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-132610DOI: 10.1080/00268976.2016.1235736OAI: oai:DiVA.org:liu-132610DiVA: diva2:1047074
Available from: 2016-11-16 Created: 2016-11-16 Last updated: 2016-11-17Bibliographically approved
In thesis
1. Computational Design of Molecular Motors and Excited-State Studies of Organic Chromophores
Open this publication in new window or tab >>Computational Design of Molecular Motors and Excited-State Studies of Organic Chromophores
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents computational quantum chemical studies of molecular motors and excited electronic states of organic chromophores.

The first and major part of the thesis is concerned with the design of light-driven rotary molecular motors. These are molecules that absorb light energy and convert it into 360° unidirectional rotary motion around a double bond connecting two molecular halves. In order to facilitate potential applications of molecular motors in nanotechnology, such as in molecular transport or in development of materials with photo-controllable properties, it is critical to optimize the rates and efficiencies of the chemical reactions that produce the rotary motion. To this end, computational methods are in this thesis used to study two different classes of molecular motors.

The first class encompasses the sterically overcrowded alkenes developed by Ben Feringa, co-recipient of the 2016 Nobel Prize in Chemistry. The rotary cycles of these motors involve two photoisomerization and two thermal isomerization steps, where the latter are the ones that limit the attainable rotational frequencies. In the thesis, several new motors of this type are proposed by identifying steric, electronic and conformational approaches to accelerate the thermal isomerizations. The second class contains motors that incorporate a protonated Schiff base and are capable to achieve higher photoisomerization rates than overcrowded alkene-based motors. In the thesis, a new motor of this type is proposed that produces unidirectional rotary motion by means of two photochemical steps alone. Also, this motor lacks both a stereocenter and helical motifs, which are key features of almost all synthetic rotary motors developed to date.

The second part of the thesis focuses on the design and assessment of composite computational procedures for modeling excited electronic states of organic chromophores. In particular, emphasis is put on developing procedures that facilitate the calculations of accurate 0−0 excitation energies of such compounds in a cost-effective way by combining quantum chemical methods with different accuracies.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. 64 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1794
National Category
Theoretical Chemistry Organic Chemistry Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-132611 (URN)10.3384/diss.diva-132611 (DOI)9789176856741 (Print) (ISBN)
Public defence
2016-12-15, Schrödinger (E324), Fysikhuset, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2016-11-16 Created: 2016-11-16 Last updated: 2016-11-17Bibliographically approved

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