Competition between ultrafast relaxation and photoionization in excited prefluorescent states of tryptophan and indole.
The quantum yield of photoionization of TrpH and IndH from the nonrelaxed prefluorescent state S* increases with the temperature decrease. This effect is attributed to the competition between temperature independent ionization and ultrafast thermal relaxation S* --> S1. The rate constant of the relaxation does not depend on the solvent and on the presence of the amino acid side chain: the temperature dependences of photoionization quantum yield, obtained for TrpH and IndH in different solvents, practically coincide. The activation energy for the relaxation rate constant Er approximately 4.5 kJ/mol probably corresponds to intramolecular process or to the formation of the vibronically excited transient complex between photoexcited molecule and solvent molecules.
Sherin
P S
PS
International Tomography Center, 630090 Novosibirsk, Russia and Novosibirsk State University, 630090 Novosibirsk, Russia.
Snytnikova
O A
OA
Tsentalovich
Yu P
YP
Sagdeev
R Z
RZ
D005453:Fluorescence; D007211:Indoles / Q000737:chemistry*; D008956:Models, Chemical; D010782:Photolysis; D014364:Tryptophan / Q000737:chemistry*
D007211:Indoles; C030374:indole; D014364:Tryptophan