Biphotonic ionization of kynurenine and 3-hydroxykynurenine

The photoionization of kynurenine (KN) and 3-hydroxykynurenine (3OHKN) in aqueous solutions proceeds via a biphotonic mechanism. The precursors for ionization are the triplet states TKN and T3OHKN, absorbing the second light quantum. The addition of solvated electrons to the parent molecules with the rate constant 2.0 × 1010 M−1 s−1 results in the formation of anion radicals, the latter in neutral solutions undergoes fast protonation. The individual spectra of all intermediates – triplet states, cation radicals, electron adducts – formed under UV irradiation of KN and 3OHKN are obtained.