Photoinduced electron and proton transfer

A. L. Sobolewski and W. Domcke, Photoinduced electron and proton transfer in phenol and its clusters with water and ammonia, J. Phys. Chem. A, 105 (2001) 9275-9283. 

Sobolewski, A. L., Domcke, W., Photoinduced Electron and Proton Transfer in Phenol and Its Clusters with Water and Ammonia, J. Phys. Chem. A 2001, 105, 9275 9283. 

Photoinduced Electron and Proton Transfer in a Molecular Triad... 

Frutos LM, Markmann A, Sobolewski AL, Domcke W Photoinduced electron and proton transfer in the hydrogen-bonded pyridine-pyrrole system. J Phys Chem B 2007, lll(22) 6l 10-6112. 

Interfacial electron transfer at solid-liquid interfaces, photoinduced and/or in the presence of an applied potential bias, as in the case of water oxidation on semiconducting metal oxide electrodes involves, as will be discussed in the next section, multiple electron and proton transfer steps. The energy cost associated with charge transfer across the interface will translate into overpotentials for driving the (photo)electrochemical reactions. This is particularly significant in... 

The second group of intermolecular reactions (2) includes [1, 2, 9, 10, 13, 14] electron transfer, exciplex and excimer formations, and proton transfer processes (Table 1). Photoinduced electron transfer (PET) is often responsible for fluorescence quenching. PET is involved in many photochemical reactions and plays... 

Thus, a number of processes may take place within supramolecular systems, modulated by the arrangement of the components excitation energy migration, photoinduced charge separation by electron or proton transfer, perturbation of optical transitions and polarizabilities, modification of redox potentials in ground or excited states, photoregulation of binding properties, selective photochemical reactions, etc. 

We have discussed recent computational and spectroscopic results on the photoinduced hydrogen transfer and proton transfer chemistry in hydrogen-bonded chromophore-solvent clusters. The interplay of electronic spectroscopy of size-selected clusters and computational studies has led to a remarkably detailed and complete mechanistic picture... 

Electron, energy and proton transfer or molecular rearrangements are the most important events that occur in interfacial supramolecular assemblies. In this chapter, the general theories of electron transfer, both within ISAs and across the film/electrode interface, are described. Moreover, photoinduced electron, energy and proton transfer processes are discussed. As this book focuses on supramolecular species, the treatment is restricted to intramolecular or interfacial processes without the requirement for prior diffusion of reactants. 

From ratios of quantum yield expressions (equation 5) for triads 1 and 2 and the rate constants calculated above, it is possible to compare the yields of key pathways in the two triads. Numerical evaluation of these ratios requires the assumption that the yield of step 7 is unity. This is reasonable as the lifetime of analogous charge-separated states in triads lacking proton transfer is at least 70 ns and proton transfer is subpicosecond in triad 1. Because the yield of photoinduced electron transfer (step I) is essentially unity, the yield of electron donation to the porphyrin radical cation by the carotenoid in 2, which is analo-... 

When this probability is equal to 1 (uniform concentration), the reaction is of pseudo-first order. This is the case, for example, in photoinduced proton transfer in aqueous solutions from an excited acid M (=AH ) (see Section 4.5) M is always within the encounter distance with a water molecule acting as a proton acceptor, and thus proton transfer occurs effectively according to a unimolecular process. This is also the case of photoinduced electron transfer in aniline or its derivatives as solvents an excited acceptor is always in the vicinity of an aniline molecule as an electron donor. In both cases, the excited-state reaction occurs under non-diffusive conditions and is of pseudo-first order. 

In almost all applications, fluorescent pH indicators are employed in a pH range around the ground state pKa (even if the excited state pK is different). Therefore, the absorption (and excitation) spectrum depends on pH in the investigated range. These indicators can be divided into three classes (see formulae in Figure 10.2) on the basis of the elementary processes (photoinduced proton transfer or electron transfer) that are involved. 

Class C Fluorophores that undergo no photoinduced proton transfer but only photoinduced electron transfer. The fluorescence quantum yield of these fluorophores is very low when they are in the non-protonated form because of internal quenching by electron transfer. Protonation (which suppresses electron transfer) induces a very large enhancement of fluorescence (see Section 10.2.2.5). The bandshapes of the excitation and fluorescence spectra are independent of pH. 

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