Ionochromism, solvatochromism and effect of dissolved gases on the spectral properties of bromothymol blue

The color of the pH indicator Bromothymol blue (BTB) changes from yellow to blue with increasing pH. The effect of some electrolytes (LiCl, NaCl, KCl, CsCl, KSCN and KClO₃) and of D₂O on the spectral properties of dilute solutions of BTB is explored. The results are interpreted in terms of dimerization of the dye molecules and of the different hydration that D₂O induces. The effects of dissolved gases on the spectral properties of BTB is studied. Complete removal of dissolved gas is achieved. Surprising effects on the UV–vis spectra emerged. After degassing solutions, gases were re-admitted via bubbling. The gases He, Ar, N₂, CO₂ and CH₄.were studied. The effects can be explained by presence or absence of nano- and microbubbles of gas in the solution. These allow formation of dimers and multiple association via adsorption and so affect the spectral properties of the dye molecules.