Spectroscopic observations on photofading and fluorescence changes of eosin Y solutions in the presence of sodium azide

Eosin Y solutions exposed to illumination with visible light showed a decreased absorption at 513 nm with increasing irradiation time. In the presence of the singlet oxygen quencher sodium azide, photofading at 513 nm was somewhat lower and a new and small absorption band at 420 nm was observed. Eosin Y fluorescence at 538 nm also decreased with illumination, while a new emission peak appeared at 478 nm. The presence of sodium azide largely increased the photoinduced emission at 478 nm.