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Synthèse et caractérisation de nouveaux complexes photo-actifs à base de fer

Abstract : This thesis work deals with the design of new organoferrous photosensitizers as an alternative to those commonly used based on noble metals such as ruthenium. However, the replacement of ruthenium with iron for optoelectronic applications is a great challenge due to the high propensity of iron complexes to undergo a fast deactivation of their excited states by lower-lying high-spin MC states. In this context, we have synthesized and characterized various series of homoleptic iron(II) complexes bearing bidentate pyridyl-carbene ligands. These ligands allow these complexes to reach geometry closer to the octahedral one which results in a stronger ligand-field, destabilizing the MC states and thus increasing their lifetimes. These different complexes were characterized by UV-visible spectroscopy, electrochemistry, femtosecond transient absorption spectroscopy and DFT calculations. At a first stage, the impact of the ligand arrangement around the metal center on photophysical properties has been studied, showing a strong influence of fac/mer isomerism. Indeed, the facial isomer possesses a slower 3MLCT relaxation compared to that of the meridional. Furthermore, variations in the carbene unit have also been carried out. It has been shown that increasing the π-conjugation or the presence of additional heteroatoms in the NHC moiety leads to a significant destabilization of the MC states, reaching remarkable 3MLCT excited state lifetimes up to 25 ps. Based on these results, the most promising complexes have been modified by introducing carboxylic acid functional groups in view of their chemisorption on a TiO2 photoanode and a possible application as sensitizers for dye-sensitized solar cells (DSSC).
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https://hal.univ-lorraine.fr/tel-02877340
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Kevin Magra. Synthèse et caractérisation de nouveaux complexes photo-actifs à base de fer. Chimie. Université de Lorraine, 2019. Français. ⟨NNT : 2019LORR0325⟩. ⟨tel-02877340⟩

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