3-Hydroxybenzo[g]chromones: Fluorophores with red-shifted absorbance and highly sensitive to polarity emission

Solvatochromic probes based on 3-hydroxychromones are often used to study interactions of biomolecules in spectroscopy and microscopy setups. However, due to their UV or violet absorbance these probes have limited application for live-cell imaging. In this work, we developed a series of benzochromones with red-shifted absorbance by introducing a fused benzene ring and substituents with extended π-electron conjugated system in the position 2. Developed 3-hydroxybenzo[g]chromones demonstrated improved sensitivity to the polarity of local environment when compared to other known solvatochromic dyes absorbing in the same spectral region. We tuned the fluorescence properties of benzochromones by varying the substituents in the position 2. Thus 2-(6′-dimethylaminobenzofuryl)-3-hydroxybenzochromone (BFBC) showed two emission bands in hydrophobic environments due to the ESIPT reaction and providing a ratiometric response highly sensitive to the polarity of the dye environment. We found that BFBC is a suitable dye for fluorescence microscopy and in contrast to other known 3-hydroxychromones, BFBC possesses a convenient excitation with a common 488 nm argon laser. Together with high solvatochromism and ratiometric response it makes BFBC a prospective fluorophore for probe development and application in biological research.