The Effect of Ammonia Ions on the Absorption and Fluorescence of an Oxazine Dye

The addition of ammonium hydroxide to a weakly acidic oxazine perchlorate dye produces a color change by means of a deprotonation mechanism in which the hydroxyl radical abstracts a loosely bound proton, leaving the positively charged ammonium cation to counter balance the perchlorate anion. This reaction produces significant absorption and fluorescence band shifts which can be accounted for by a semi-classical oscillator model predicting two dichroic electronic band systems associated with this dye. Peculiar wavelength excitation dependent fluorescence band shifts are attributed to overlapping triplet states simultaneously excited.