Doctoral defence in Chemistry - Ivan Tambovtsev

Doctoral candidate: Ivan Tambovtsev

Title of thesis: Molecular Motors and Chiral Media

Opponents:
Dr. Gísli Hólmar Jóhannesson, Chemistry & Mathematics Teacher at Keilir, Iceland
Dr. Karl-Heinz Ernst, Professor at the University of Zurich and EMPA, Switzerland

Advisor: Dr. Hannes Jónsson, Professor at the Faculty of Physical Sciences, University of Iceland

Other members of the doctoral committee:
Dr. Elvar Örn Jónsson, Research Assistant Professor at the Science Institute, University of Iceland
Dr. Sergei Egorov, Professor at the Department of Chemistry, University of Virginia, USA
Dr. Tetiana Orlova, Senior Researcher at the Institute of Physics, Yerevan State University, Armenia
Dr. Gianluca Levi, Associate Professor at the University of Trieste, Italy, and Adjunct at the Faculty of Physical Sciences, University of Iceland

Chair of Ceremony: Dr. Benjamín R. Sveinbjörnsson, Professor and Vice Head of the Faculty of Physical Sciences, University of Iceland 

Abstract

Light-driven second-generation molecular motors offer a route to controllable nanoscale motion and energy conversion. This dissertation applies established electronic-structure methods to quantify and tune their photophysical and kinetic properties, with emphasis on both the optical absorption that initiates rotation, characterized using time-dependent density functional theory (TDDFT), and the thermal steps that set the overall timescale of rotation. The limitations of standard TDDFT for complex, multi-chromophoric systems are also assessed, validating a time-independent orbital-optimized approach for systems featuring coupled chromophores and spatially separated excitations. Minimum-energy paths are obtained with the climbing-image nudged elastic band method using energy and atomic forces coming from density functional theory calculations, and rate constants are estimated via harmonic transition state theory. Two general substitution patterns emerge across representative overcrowded-alkene scaffolds. Replacing the methyl group at the stereogenic center by bulkier or more electronegative substituents such as trifluoromethyl, trichloromethyl, tert-butyl, or fully fluorinated tert-butyl consistently increase the rotational speed and often enlarges the spectral separation between stable and metastable states, improving selective photo-addressability. In contrast, replacing hydrogen at the stereogenic center by fluorine or chlorine slows down the rotation, narrows the spectral gap, and can even alter the reaction mechanism by favoring a competing pathway. Across all systems studied, barrier shifts dominate the kinetics while the prefactor does not change much. These results establish simple chemical rules for controlling the timescale and spectral properties of molecular motors through targeted substitution. Beyond benchmarking motor–motor comparisons, these guidelines support the design of responsive materials, including motor-doped cholesteric liquid crystals, where light-controlled actuation, reconfigurable photonics, and the transport of chiral textures - which are shown to be governed by attractive and anisotropic inter-soliton forces - become accessible. The unified workflow from density functional theory to minimum-energy paths and harmonic transition state theory provides a practical route to predict and optimize motor performance in diverse materials contexts. 

About the doctoral candidate

Ivan Tambovtsev completed his B.Sc. and M.Sc. degrees in Physics at Saint Petersburg State University, where he also carried out advanced research in theoretical and computational physics.
He began his doctoral studies at the Faculty of Physical Sciences, University of Iceland, in 2022.
His research focuses on computational modelling of molecular motors, chiral media, and related nanoscale systems, under the supervision of Professor Hannes Jónsson.