245 research outputs found
Dynamics of excited-state proton transfer systems via time-resolved photoelectron spectroscopy
The use of time-resolved photoelectron spectroscopy for analyzing excited state intramolecular proton transfer (ESIPT) and internal conversion dynamics in a model system was investigated. The photoelectron spectra of both the excited state enol and keto tautomers were presented as a function of pump laser wavelength and pump-probe time delay. It was found that the internal conversion dynamics in o-hydroxybenzaldehyde (OHBA) was influenced by interactions with a close-lying n??* state.open958
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Two-photon, visible light water splitting at a molecular ruthenium complex
Water splitting to give molecular oxygen and hydrogen or the corresponding protons and electrons is a fundamental four-electron redox process, which forms the basis of photosynthesis and is a promising approach to convert solar into chemical energy. Artificial water splitting systems have struggled with orchestrating the kinetically complex absorption of four photons as well as the difficult utilization of visible light. Based on a detailed kinetic, spectroscopic and computational study of Milstein's ruthenium complex, we report a new mechanistic paradigm for water splitting, which requires only two photons and offers a new method to extend the range of usable wavelengths far into the visible region. We show that two-photon water splitting is enabled by absorption of the first, shorter wavelength photon, which produces an intermediate capable of absorbing the second, longer wavelength photon (up to 630 nm). The second absorption then causes OâO bond formation and liberation of O2. Theoretical modelling shows that two-photon water splitting can be used to achieve a maximum solar-to-hydrogen efficiency of 18.8%, which could be increased further to 28.6% through photochemical instead of thermal H2 release. It is therefore possible to exceed the maximum efficiency of dual absorber systems while only requiring a single catalyst. Due to the lower kinetic complexity, intrinsic utilization of a wide wavelength range and high-performance potential, we believe that this mechanism will inspire the development of a new class of water splitting systems that go beyond the reaction blueprint of photosynthesis
Dynamics of Excited State Proton Transfer in Nitro Substituted 10-Hydroxybenzo[h]quinolines
Barrierless proton transfer in HBQ and a barrier upon nitro substitution.</p
Semiclassical model of ultrafast photoisomerization reactions
In this letter we propose a model which explains ultrafast and efficient
photoisomerization reactions as driven by transitions between quasistationary
states of one dimensional (1D) double well potential of an excited electronic
state. This adiabatic potential is formed as a result of doubly crossing of a
decay diabatic potential of the ground electronic state and a bound diabatic
potential of the excited state. We calculate the eigenstates and eigenfunctions
using the semiclassical connection matrices at the turning and crossing points
and the shift matrices between these points. The transitions between the
localized in the wells below the adiabatic barrier states are realized by the
tunneling and by the double non-adiabatic transitions via the crossing points
processes. Surprisingly the behavior with the maximum transition rate keeps
going even for the states relatively far above the barrier (2 -4 times the
barrier height). Even though a specific toy model is investigated here, when
properly interpreted it yields quite reasonable values for a variety of
measured quantities, such as a reaction quantum yield, and conversion time.Comment: 9 pages, 5 figures. accepted to Chem. Phys. Letters (2005
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