Figure 2.

Optical properties of pyranine and substrates. (A) Excitation and emission spectra of pyranine 1 and substrate 7 (serves as a proxy; data representative for all ethers in this study) in different buffers with pH values varying between pH 4.0 and pH 11.8; lower pH values are indicated by increasingly darker graph shade and emission data for pyranine 1 recorded using excitation at 450 nm. (B) Emission values shown as a function of pH at two different excitation wavelengths corresponding to different protonation states of pyranine; buffer type as indicated by colour. (C) Visualization of droplets containing pyranine dissolved in buffer with different pH values confirms ability to detect pyranine over broad pH range; fluorescein and resorufin samples were included as positive controls for leakage experiments at pH 8.0. (D) Leakage of fluorescent dyes from aqueous droplets (n=10, error bars show standard deviation) as a function of time; results indicate stable retention of pyranine 1 in droplets under all pH values tested.