Fluorescence Quenching of Benzaldehyde in Water by Hydrogen Atom Abstraction.
We computed the mechanism of fluorescence quenching of benzaldehyde in water through relaxed potential energy surface scans. Time-dependent density functional theory calculations along the protonation coordinate from water to benzaldehyde reveal that photoexcitation to the bright ππ* (S3 ) state is immediately followed by ultrafast decay to the nπ* (S1 ) state. Evolving along this state, benzaldehyde (BA) abstracts a hydrogen atom, resulting in a BAH(.) and OH(.) radical pair. Benzaldehyde does not act as photobase in water, but abstracts a hydrogen atom from a nearby solvent molecule. The system finally decays back to the ground state by non-radiative decay and an electron transfers back to the OH(.) radical. Proton transfer from BAH(+) to OH(-) restores the initial situation, BA in water.
Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Ruprecht-Karls Universität Heidelberg, Im Neuenheimer Feld 368, 69120, Heidelberg, Germany.
Katharyn
K
Fletcher
Organisch-Chemsches Institut, Ruprecht-Karls Universität Heidelberg, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany. uwe.bunz@oci.uni-heidelberg.de.
Uwe H F
UH
Bunz
Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Ruprecht-Karls Universität Heidelberg, Im Neuenheimer Feld 368, 69120, Heidelberg, Germany. dreuw@uni-heidelberg.de.
Andreas
A
Dreuw
excited-state hydrogen transfer; fluorescence quenching; photobasicity; photochemistry; quantum chemistry