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On the possibility to accelerate the thermal isomerizations of overcrowded alkene-based rotary molecular motors with electron-donating or electron-withdrawing substituents
Linköping University, Department of Physics, Chemistry and Biology, Bioinformatics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Bioinformatics. Linköping University, Faculty of Science & Engineering.
2016 (English)In: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 22, no 9, 219- p.Article in journal (Refereed) Published
Abstract [en]

We employ computational methods to investigate the possibility of using electron-donating or electron-withdrawing substituents to reduce the free-energy barriers of the thermal isomerizations that limit the rotational frequencies achievable by synthetic overcrowded alkene-based molecular motors. Choosing as reference systems one of the fastest motors known to date and two variants thereof, we consider six new motors obtained by introducing electron-donating methoxy and dimethylamino or electron-withdrawing nitro and cyano substituents in conjugation with the central olefinic bond connecting the two (stator and rotator) motor halves. Performing density functional theory calculations, we then show that electron-donating (but not electron-withdrawing) groups at the stator are able to reduce the already small barriers of the reference motors by up to 18 kJ mol(-1). This result outlines a possible strategy for improving the rotational frequencies of motors of this kind. Furthermore, exploring the origin of the catalytic effect, it is found that electron-donating groups exert a favorable steric influence on the thermal isomerizations, which is not manifested by electron-withdrawing groups. This finding suggests a new mechanism for controlling the critical steric interactions of these motors.

Place, publisher, year, edition, pages
SPRINGER , 2016. Vol. 22, no 9, 219- p.
Keyword [en]
Electronic effects; Molecular motors; Quantum chemistry; Rotary rates; Steric effects
National Category
Theoretical Chemistry
URN: urn:nbn:se:liu:diva-131672DOI: 10.1007/s00894-016-3085-yISI: 000382748100024PubMedID: 27553304OAI: diva2:1014929

Funding Agencies|Linkoping University; Swedish Research Council [621-2011-4353]; Olle Engkvist Foundation; Carl Trygger Foundation

Available from: 2016-10-03 Created: 2016-09-30 Last updated: 2016-11-16
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.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1794
National Category
Theoretical Chemistry Organic Chemistry Chemical Sciences
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)
Available from: 2016-11-16 Created: 2016-11-16 Last updated: 2016-11-17Bibliographically approved

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