Fig. 1

Spectroscopic properties of HFI. A Fluorescence spectra of HFI (10 μM) in methanol containing increasing concentrations of glycerol. B Dependence of Log(I) on Log(η). Log(I ₆₁₀) = 0.3777*Log(η) + 1.328 (R² = 0.9609), Log(I ₄₆₀) = 0.2250*Log(η) + 1.144 (R² = 0.9669), Log(I ₆₁₀/I ₄₆₀) = 0.1527*Log(η) + 0.1834 (R² = 0.9400). C Emission spectra of the probe in PBS buffer with different pH values (3–10). D Plots of the I ₆₁₀/I ₄₆₀ versus pH. E Plots of I ₆₁₀/I ₄₆₀ versus pH in various proportions of glycerin and different pH PBS buffer. F Photostability experiments of HFI (10 μM) in PBS buffer (pH 4 or pH 8), PBS buffer (pH 4) / glycerin (2/5, v/v), or glycerin under continuous irradiation by laser light. λ_ex = 400 nm