Dithieno[2,3‐b-3,2‐f]phosphepinium‐Based Near‐Infrared Fluorophores: px‐π* Conjugation Inherent to Seven‐Membered Phosphacycles - Archive ouverte HAL
Article Dans Une Revue Angewandte Chemie International Edition Année : 2024

Dithieno[2,3‐b-3,2‐f]phosphepinium‐Based Near‐Infrared Fluorophores: px‐π* Conjugation Inherent to Seven‐Membered Phosphacycles

Keita Andoh
  • Fonction : Auteur
Masahito Murai
  • Fonction : Auteur correspondant
Muriel Hissler
Shigehiro Yamaguchi

Résumé

Positively charged phosphorus-containing heterocycles are characteristic core skeletons for functional molecules. While various phosphonium-containing five- or six-membered ring compounds have been reported, seven-membered ring phosphepinium has not yet been fully studied. In this study, dithieno[2,3-b;3,2-f]phosphepinium ions containing electron-donating aminophenyl groups were synthesized. An X-ray crystallographic analysis of the resulting donor-acceptor-donor dyes revealed a bent conformation of the central seven-membered ring. This compound exhibited fluorescence in the near-infrared region with a bathochromic shift of 70 nm compared to phosphepine oxide congener and a large Stokes shift. High fluorescence quantum yields were obtained even in polar solvents due to the suppression of the nonradiative decay process. The theoretical study revealed that the phosphepinium skeleton is highly electron-accepting owing to the orbital interaction between a px orbital of the phosphonium moiety and a π* orbital of the 1,3,5-hexatriene moiety. Owing to the lower-lying px orbital in the phosphonium moiety compared with that of the phosphine oxide and the bent conformation of the seven-membered ring, the phosphepinium ring effectively furnishes a px-π* conjugation. A large structural relaxation with the contribution of a quinoidal resonance structure is suggested in the excited state, which is responsible for the intense emission with a large Stokes shift.
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hal-04646353 , version 1 (16-08-2024)

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Keita Andoh, Masahito Murai, Pierre-Antoine Bouit, Muriel Hissler, Shigehiro Yamaguchi. Dithieno[2,3‐b-3,2‐f]phosphepinium‐Based Near‐Infrared Fluorophores: px‐π* Conjugation Inherent to Seven‐Membered Phosphacycles. Angewandte Chemie International Edition, 2024, ⟨10.1002/anie.202410204⟩. ⟨hal-04646353⟩
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