Phosphorescence Quenching by External Molecules

Fluorescence quenching has proven to be a powerful means to determine location of tryptophans. Small organic molecules, such as acetone, acrylamide, and amino acids, have been used to quench fluorescence of tryptophans which are exposed to the solvent.(50 51) These molecules apparently quench by close interaction and so provide a tool to determine the surface accessibility7 of tryptophan in a protein. 

The same rationale which is used for fluorescence quenching can be used 

The Stem-Volmer(52) equation relates fluorescence intensity and the quenching rate constant, kq  

Making the assumption that kiac is fast, we can modify Eq. (3.9) to yield  

A survey of the quenching constants for a series of proteins was made using one quencher, nitrite (Table 3.4).(58) It is noted that the phosphorescence lifetime t0 is not correlated with the quenching constant. For example, the 

---