Multi-Scale Quantum Chemistry Investigation of Molecular Switches
: From Solution to Crystal

Student thesis: Doc typesDoctor of Sciences

Abstract

This thesis aims at studying molecular switches in different media. In a first part, several chapters are dedicated to crystalline N-salicylideneaniline (anil) derivatives, which switch between an enol (E) and a keto (K) form. In a preliminary step, three exchange-correlation functionals (XCFs) and an atomic basis set have been selected, based on their performance compared to X-ray diffraction data to reproduce the molecular geometries, unit cell parameters, and relative E ⇌ K energies of three anils. This has enabled the study of the effects of co-crystallization on the E ⇌ K equilibrium of an anil, PYV3, and on its geometry, explaining the reduced thermochromism. Then, using an embedding scheme that reproduces the crystalline Colombic potential, the nuclear magnetic resonant (NMR) isotropic shielding values of PYV3 and of two of its co-crystals have been predicted, in view of enabling the interpretation of experimental data. Using this embedding scheme, the UV/Vis absorption spectra of PYV3 and its co-crystals have been modeled, allowing the interpretation of experimental spectra and a better understanding of the underlying geometrical and crystal field effects of co-crystallization. Then, anil-based covalent organic frameworks have been investigated, focusing on their relative energy, geometries, and linear and nonlinear optical (NLO) properties, giving a proof-of-concept of their potential as NLO-phores, as well as offering design guidelines. In a second part, molecular switches in solution are investigated. First, high-level methods [MP2 and CCSD(T)] are used to determine the equilibria of two anil (E ⇌ K) and three spiropyran (S)/merocyanine (M) (S ⇌ M) switches, reaching very close agreement with experiments. Then, multistate molecular switches have been studied. The NMR isotropic shielding values of a benzazolooxazolidine (BOX) dithienylethene (DTE) hybrid have been modeled, which, combined with experiments, explains its gated-photochromism. Finally, a new family of switches, composed of two identical BOX units, and therefore three states, have been studied. It is demonstrated that their three states can be accessed in a controlled way and that they present large NLO contrasts. The role of the linker between the BOX units has been unraveled in view of improving their switching properties.
These different contributions show the central role of computational chemistry methods to interpret experimental data, to deduce structure-property relationships, and to contribute to the design of new intelligent molecules.
Date of Award8 Oct 2020
Original languageEnglish
Awarding Institution
  • University of Namur
SponsorsARC (Actions de recherche concentrées)
SupervisorBenoit CHAMPAGNE (Supervisor), Yoann Olivier (President), Luc Henrard (Jury), JOHAN WOUTERS (Jury), Tom Leyssens (Jury) & Lorenzo Maschio (Jury)

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