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Selective Conversion of P=O‐Bridged Rhodamines into P=O‐Rhodols: Solvatochromic Near‐Infrared Fluorophores
Author(s) -
Grzybowski Marek,
Taki Masayasu,
Yamaguchi Shigehiro
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201703456
Subject(s) - solvatochromism , bathochromic shift , xanthene , chemistry , photochemistry , aqueous solution , fluorescence , fluorophore , moiety , merocyanine , toluene , solvent , stereochemistry , organic chemistry , photochromism , physics , quantum mechanics
The substitution of an oxygen atom in rhodols with a phosphine oxide (P=O) moiety affords P=O‐bridged rhodols as a new type of near‐infrared (NIR) fluorophore. This compound class can be readily accessed upon exposure of the corresponding rhodamines to aqueous basic conditions. The electron‐withdrawing effect of the P=O group facilitates the hydrolytic deamination, and, moreover, prolonged exposure to aqueous basic conditions generates P=O‐bridged fluoresceins, that is, a series of three P=O‐bridged xanthene dyes is available in one simple operation. The P=O‐bridged rhodols show significant bathochromic shifts of the longest‐wavelength absorption maximum (Δ λ =125 nm; >3600 cm −1 ) upon changing the solvent from toluene to water, whereas the emission is shifted less drastically (Δ λ =70 nm; 1600 cm −1 ). The hydrogen bonding between the P=O and C=O groups with protic solvents results in substantial stabilization of the LUMO level, which is responsible for the solvatochromism.