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Chiral-at-metal iridium(III) complexes containing dithienylethene-based photoswitchable ligands

Abstract : The main objective of this research project is the development of new photosensitive organometallic complexes based on DTE ligands for the synthesis of chiral compounds at the (“chiral-at-metal”), showing in both cases an amplification of chirality by irradiation.Chapter 1 consists of an introduction, explaining the different concepts covered during the manuscript. The first part presents some of the most interesting photochromic compounds described and focuses on the detailed explanation of the properties of dithienylethenes and their origin, applications and the isomerization mechanism. The second part of the introduction focuses on the different bis- and tris-cyclometalated Ir(III) complexes. Due to their properties, Ir(III) organometallic compounds have been widely used in different applications such as OLEDs, target compounds in biological systems, or as anticancer systems.Chapter 2 presents the studies carried out to obtain octahedral complexes with cyclometalated DTE ligands. The first part of the chapter is based on the synthesis and characterization of different DTE ligands. Synthesized photochromic ligands can be categorized into symmetric or non-symmetric ligands, depending on the composition of the thiophene groups in the structure. All ligands are designed in such a way that the coordination point is through a thiophene-pyridyl group, which can vary the position in the structure of the compound. The second part of the chapter focuses on obtaining the coordination of the previously synthesized ligands to different Ir(III) precursors.Chapter 3 presents the studies carried out to obtain octahedral complexes with non-symmetrical DTE ligands containing bipyridine groups as coordinating centers. The first section of the chapter is based on the synthesis and characterization of four previously undescribed DTE ligands. The second section of Chapter 3 is divided into two parts: the synthesis of racemic complexes and the synthesis of enantiopure complexes. In the first part, the coordination of DTE ligands to a racemic Ir(III) center will be briefly discussed. These were the preliminary tests carried out for the correct functioning of the coordination study of the synthesized ligands to enantiopure Ir(III) centers.Chapter 4 collects the results obtained to study the different properties, both for the DTE ligands and the corresponding complexes. The chapter begins with the photochromic study of the different DTE ligands with a bipyridine group in their structure. The photochromic character was studied, observing how the absorption spectra varied depending on whether the ligand was in the open or closed form, identifying bands characteristic of both isomers. Kinetic studies were carried out, both by NMR spectroscopy and by UV-Vis spectroscopy, in order to calculate the quantum yields of the photophysical processes present in the isomerization of DTE. To finalize the study of the ligands, the properties of resistance against fatigue and the thermal stability of the closed isomers were verified. The second part of the chapter includes the repetition of the studies carried out for the Ir(III) complexes. The effect of metal coordination on the displacement of the absorption maxima of the compounds was studied, observing a shift towards the red of the different absorption bands. The efficiency of the photocyclization/photocycloreversion processes (QY) was also studied. The comparison of the quantum yields between the free ligands and the Ir(III) complexes showed that the coordination to the metal center does not significantly affect the photochemical process. Following the guidelines of the DTE ligands, the fatigue resistance was studied. Finally, the induction of a diastereoselective isomerization of the enantiopure complexes was studied using circular dichroism spectroscopy.
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Submitted on : Thursday, June 30, 2022 - 5:06:12 PM
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Francisco Urquiola. Chiral-at-metal iridium(III) complexes containing dithienylethene-based photoswitchable ligands. Other. Université de Bordeaux; Universidad del País Vasco, 2022. English. ⟨NNT : 2022BORD0057⟩. ⟨tel-03710490⟩

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