Inversion of the Deactivation Efficiency of Excited States upon Selective Photoexcitation of the Uranyl Ion Complex with D-Tryptophan in Aqueous and Methanol Solutions

The quenching of fluorescence (FL) of uranyl ion $${\text{UO}}_{2}^{{2 + }}$$ and tryptophan Trp during their selective intracomplex photoexcitation in aqueous and methanol solutions has been studied. The Stern–Volmer constants have been determined for all studied systems. A static FL quenching mechanism has been established. It has been found that only intracomplex photoinduced electron transfer (PET) from Trp to $${\text{UO}}_{2}^{{2 + }}$$ is observed in aqueous solutions, regardless of the type of photoexcitation. In the case of excitation of the Trp⋅⋅⋅ $${\text{UO}}_{2}^{{2 + }}$$ complex in CH3OH, a competing intermolecular photoinduced transfer of a hydrogen atom from methanol to the electronically excited uranyl ion is observed along with the PET.