Phosphorescence dissolved molecular oxygen quenching

Because of the long radiative lifetime of the lowest triplet state, most phosphorescence in fluid solutions is obviated by collisional quenching, especially by dissolved molecular oxygen. Phosphorescence, when it occurs, is usually observed at low temperatures (e.g., that of liquid nitrogen) in rigid matrices where it may demonstrate high quantum yields. In the past three decades, much interest has been focused on phosphorescence at room temperature (RTP), which sometimes can be observed in samples adsorbed on solid substrates such as filter paper. Unfortunately, the quantum yields observed in room temperature phosphorescence are low, leading to poor analytical sensitivity, and the method has not enjoyed wide popularity. Phosphorescent measurements at low temperatures... 

Dissolved molecular oxygen can quench both fluorescence and phosphorescence albeit with different efficiencies and mechanisms. The extent of oxygen quenching on fluorescence is strongly dependent on the fluorophore, whereas for phosphorescence the intensity is always adversely affected. This can be rationalized using the Stern-Volmer equation [4] assuming no other quenching species are present. 

The solution was contained in a cylindrical Pyrex or silica optical cell, 2.5 cm. in diameter and 2 cm. optical depth, fitted with a side arm of diameter about 1 cm. for connection to the vacuum line (see Fig. 10). Both phosphorescence and delayed fluorescence in fluid solution at room temperature are quenched by exceedingly low concentrations of molecular oxygen, and efficient deaeration is of the utmost importance. The following procedure was found to be satisfactory. The cell was first cooled in an acetone/C02 bath and pumped out. It was then isolated from the pump, refluxed to remove dissolved gas, cooled again in the... 

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