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Synthesis, Electronic Properties, and Reactivity of Phospholes and 1,1′-Biphospholes Bearing 2- or 3-Thienyl C-Substituents

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Abstract

PS, I love you! Novel mixed phosphole/thiophene π-conjugated systems were synthesized and their electronic properties have been studied both experimentally by UV/Vis spectroscopy and electrochemistry and by theoretical calculations. Exploiting the chemistry of both P- and S-heteroles allows the generation of a diverse range of novel ring-fused benzophosphole–thiophene derivatives.

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Two series of phospholes and 1,1′-biphospholes bearing either 2- or 3-thienyl substituents at the C atoms are prepared by using the Fagan–Nugent route. Their optical (UV/Vis absorption, fluorescence spectra) and electrochemical properties are systematically evaluated. Of particular interest, the first ever reported 3-thienyl-substituted phospholes exhibit higher LUMO levels than their 2-thienyl analogues, and show accordingly different physical properties. This study also reveals that the 1,1′-biphospholes exhibit σ–π conjugation. The phosphole and 1,1′-biphosphole derivatives bearing 3-thienyl substituents are characterized by X-ray diffraction study. The structure–property relationship established following the experimental data are fully supported by theoretical studies including time-dependent(TD)-DFT spectra. A photocyclization reaction performed on the thioxo- and oxophospholes having 3-thienyl substituents affords a novel ring-fused phosphole–thiophene derivative, which was characterized by an X-ray diffraction study. The structure and electronic properties of this novel dithienophosphole are discussed based on experimental and theoretical data.

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