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Étude par absorption transitoire de naphtopyranes liés à des oligothiophènes par différents types de jonctions

Abstract : A series of naphthopyrans, substituted in 3 and 8-position by oligothiophenes via different junctions, has been recently synthesized in order to elaborate conductive polymers, as polythiophene, having photoswitch properties. In this family, photochromism proceeds via the cleavage of the spiro-carbon – oxygen single bond. This study presents the photophysical and photochemical properties of these compounds in solution investigated by femtosecond and nanosecond transient absorption spectroscopy. We observed that the increase of the oligothiophene chain length is accompanied by the increase of the S1 state lifetime and the decrease of its energy. The increase of the conjugation between the chain and the naphtopyran moiety produces a similar effect. When the oligothiophene chain is short and weakly conjugated, the ring-opening reaction quenches the S1 state. On the contrary, when this chain becomes long and strongly conjugated, the global energy of the S1 state becomes weaker than a determinant threshold below which the photochromism mechanisms disappear. The ring-opening reaction doesn't quench S1 state and consequently its lifetime increases. In this case, we notice the formation of an unreactive triplet state and the presence of fluorescence. For some intermediate compounds, we remarked the formation of both the photomerocyanin and triplet state species. At last, substitution in 3-position by oligothiophenes supports the production of the open form by lowering the energy barrier of the ring-opening reaction.
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Baptiste Moine. Étude par absorption transitoire de naphtopyranes liés à des oligothiophènes par différents types de jonctions. Autre. Université des Sciences et Technologie de Lille - Lille I, 2006. Français. ⟨tel-00282826⟩

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