Excited singlet state decay pathways in the fluorescence probe molecule 1,8-anilinonaphthalene sulphonate (ANS)

The decay of the excited state of 1,8-anilinonaphthalene sulphonate (ANS) in aqueous and ethanolic solution has been studied by nanosecond laser flash photolysis. The rate of photoionization is found to increase rapidly as solvent polarity is increased and is the major decay route in aqueous solution, whereas in non polar solvents intersystem crossing becomes an important decay process. The very low fluorescence yield of ANS in water is thus interpreted as being caused by very rapid photoionization from the initially excited singlet state.