Abstract
In strong alkaline ices (?12M OH−), the emission of 2.8 eV of indole and tryptophan can be induced by monophotonic light of 2.85 eV. Following previous observations, we interpret this emission is due to (a) the direct phosphorescence of the solute–solvent exciplex, (b) the phosphorescence of the excited chromophore which is photodissociated from the exciplex during irradiation, and (c) the spontaneous recombination luminescence due to back reaction (chromophore cation +e−). The red end of the solute–solvent charge transfer absorption band is thus associated with prephotoionization and its tail end energy is approximately equivalent to the ionization energy Ip of the exciplex. The Ip for the solute–solvent exciplex and for the solvated electron in different aqueous matrices are linearly dependent. This leads to our deductions that (a) the solute–solvent exciplex is a ’’solvated anion’’, (b) the solvent electron affinity (E.A.) plays an important role in photoionization processes in solid solutions (increas...
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