In order to see how the spectroscopic properties of 8AQ change with pH, we performed UV-Vis pH metric titration of the 50 µm 8AQ in a range of 200 -600 nm. 8AQ was dissolved in 0.1 M NaH2PO4 solution previously adjusted to pH 3.0. Samples were titrated with small amounts of 5 M NaOH in the pH range 3-10. The obtained spectra at pH 3.00 (Figure ) show two absorption bands with λmax at 382 nm and 260 nm. Much higher absorbance at 260 nm compared to the 382 was reported previously by Steck. In addition, a very low-intensity band at 312 nm, which is characteristic of quinolines, is present (See SI UV-Vis pH metric titration of the 50 µm quinoline). A shift to the blue of the transition (260nm →247 nm) with increasing pH (NaOH additions) is observed with the gradual vanishing of 382, 312, and 260 nm bands. A spectral shift towards lower wavelengths causes the formation of two new bands with λmax at 331 nm and 247 nm. The presence of two absorbing species/forms was confirmed by isosbestic points (Ip) at 254 nm and 370 nm.