I am investigating the excited state of a pyridine N-oxide by laser flash photolysis (308 nm). I am looking for different probes to react with the excited state that can react by either one or two electron and preferably yield products which are detectable by absorbance measurements. The molecule must be soluble in either water or acetonitrile and should not absorb appreciably at 308 nm (at sub-mM concentrations). I have had success with ABTS in water (one electron oxidation of ABTS2- by the excited state followed by a back reaction yielding ABTS2- and ground state N-oxide), but the chemistry is much more complicated in acetonitrile. I have also attempted to use TMPD (in water) and tetramethylbenzidine (TMB) (in acetonitrile with varying concentrations of water). Both of the latter compounds have their own photochemistry and the varying degrees of protonation and solubility are problematic. Does anyone have any suggestions on suitable probes?