Near-infrared fluorescein dyes containing a tricoordinate boron atom

• Published in: Chemical science (Cambridge) Vol. 1; no. 33; pp. 7816 - 7821
• Main Authors: Ando, Naoki, Soutome, Hiroki, Yamaguchi, Shigehiro
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 07.09.2019; Royal Society of Chemistry
• Subjects: Boron; Chemistry; Chemistry, Multidisciplinary; Crystallography; Fluorescein; Fluorescence; Lewis acid; Near infrared radiation; Physical Sciences; Science & Technology; RED; POLYMERS; RHODAMINE DYES; POLYCYCLIC AROMATICS; BUILDING-BLOCKS; WAVELENGTH; HEAVY-CHALCOGEN ANALOGS; SCAFFOLDS; SUBSTITUTED XANTHENE DYES; PROBES
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c9sc02314c

Bora-fluoresceins ( BF s), fluorescein analogues containing a tricoordinate boron atom instead of an oxygen atom at the 10-position of the fluorescein skeleton, were synthesized as a new family of fluorescein analogues. The deprotonated BF s exhibited absorption and fluorescence in the near-infrared region, which were significantly red-shifted relative to those of hitherto-known heteroatom-substituted fluorescein analogues on account of the orbital interaction between the tricoordinate boron atom and the fluorescein skeleton. BF s also showed multi-stage changes resulting from a Lewis acid-base equilibrium at the boron center in combination with a Brønsted acid-base equilibrium at the phenolic hydroxy group. Tricoordinate boron imparts near-infrared absorption/emission and unusual multi-stage changes in the photophysical properties to fluorescein dyes.