Trianionic 1,3,2‐Dioxaborine‐Containing Polymethines: Bright Near‐Infrared Fluorophores
Vladyslav Polishchuk, Mariia Filatova, Едуард Б. Русанов, Mykola P. Shandura
Abstract
Abstract Trianionic polymethines of the A′‐π‐A‐π‐A‐π‐A′ type comprising dioxaborine rings (A) and different electron‐accepting end groups (A′) have been synthesized. The obtained dyes absorb and emit light in the near‐infrared region with remarkably high molar attenuation coefficients ( ϵ up to 495 000 M −1 cm −1 in DMF) and fluorescence quantum yields ( Φ f up to 0.73 in DMF). Thus, the novel trianionic dyes stand among the brightest individual fluorophores known to date – with a magnitude of fluorescence brightness ( ϵ ⋅ Φ f ) of 313 000 M −1 cm −1 in DMF. The synthesized dyes demonstrate a minor negative solvatochromism and small Stokes shifts. X‐ray data reveal the nearly planar geometry of the trianionic chromophore. All the obtained compounds are stable in the solid state and in a solution, although the relative stability is much higher in polar aprotic than in protic solvents.