Evaluation of solvent property of air-water interface based on the fluorescence spectra of 1,2'-dinaphthylamine in the aqueous solution of ultrafine bubbles.

Solvent property of air-water interface was evaluated based on the fluorescence spectra of 1,2'-dinaphthylamine in water containing ultrafine bubbles (average diameter: 103 nm, standard deviation: 38 nm). Among naphthylamine derivatives whose fluorescence spectra were responsive to microscopic hydrophobicity, 1,2'-dinaphthylamine (DN) was selected because its wavelength of the maximum emission (λ) was significantly dependent on the concentration and microenvironment of the ultrafine bubble. The λ value of DN in water was 486 nm, while it shifted to shorter wavelength (408 nm) in the presence of 1.