Redox quenching

As follows from the data from Sect. 2, the primary photochemical stage in the majority of the membrane systems studied is the redox quenching of the excited photosensitizer by an electron acceptor or donor leading to electron transfer across the membrane // water interface. For electron transfer to occur from the membrane-embedded photosensitizer to the water soluble acceptor, it is necessary for the former to be located sufficiently close to the membrane surface, though the direct contact of the photosensitizer with the aqueous phase is not obligatory. For example, Tsuchida et al. [147] have shown that electron transfer to MV2 + from photoexcited Zn-porphyrin inserted into the lecithin membrane, is observed only until the distance from the porphyrin ring to the membrane surface does not exceed about 12 A. 

A somewhat different type of redox quenching mechanism has been proposed for the reaction of the excited state of the Pt(II) dimer, Pt2(7/ - with... 

Scheme 7.2.17 contains another very interesting bipyridyl system, namely the ruthenium(II) complex of 2,2 -bipyridine. In this complex the d-orbitals of the ruthenium ion and the 7t-orbitals of the bipyridine are similar in energy and mix. As a result, there is almost no redox quenching of the excited singlet and triplet states and the compound fluoresces strongly, which is very unusual for a transition metal complex. It cannot only be used to produce hydrogen with the aid of viologen, but the oxidation product ruthenium(III) bipyridinate is such a... 

Photocatalytic processes in two-phase systems involve either a homogeneous photoreaction followed by the transfer of intermediate species across the interface, or a heterogeneous electron transfer between the photoactive species and the substrate. At the polarizable ITIES, both processes would manifest themselves by an increase in the current on illumination at constant potential, i.e., a photocurrent response. Indeed, photocurrent measurements have been recorded for the transfer of photogenerated ions at a liquid liquid boundary, as well as for heterogeneous redox quenching. We shall review some of these studies in this section. 

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