Amplified Heavy-Atom Free Phosphorescence from meta-Dimethoxy Difluoroboron β-Diketonate Charge-Transfer Materials

Difluoroboron β-diketonate materials are used for biomedical oxygen-sensing applications. These fluorophores show both fluorescence (F) and phosphorescence (P) when the dye is embedded in a polymer matrix. The fluorescence is insensitive to oxygen quenching, while the phosphorescence changes intensity depending on the oxygen concentration. This enables oxygen quantification by ratiometric methods with good spatial and temporal resolution. Here, we produce ratiometric-capable oxygen sensors without the need of a heavy atom. This is achieved by substituting methoxyl groups at the meta positions of an aromatic ring, dramatically influencing the electronic transitions of the fluorophore. Altering the aromatic group on the opposing ring tailors the absorption wavelength, luminescence colors, and relative fluorescence to phosphorescence ratio (F/P), which are important for oxygen sensing. The phosphorescence lifetimes are also hundreds of milliseconds long, achieving ultra-sensitivity to oxygen. This study pres...