Inner-sphere charge transfer photochemistry

Excitation to inner-sphere charge transfer (ISCT) transitions induces radial charge shift within the coordination entity, which may result in redox reactions including the central atom and ligands. The charge redistribution increases the complex susceptibility towards protonation, isomerization, redox processes, or nucleophilic or electrophilic attack. 

To compete effectively with the photophysical processes, the chemical reactions from the highly energetic CT states should be very fast, otherwise the MC states become populated. On the other hand, redox processes may sometimes occur from other than CT excited states. The phenomenon is a consequence of redox potential changes after excitation, which make the entity in any excited state a much stronger oxidant and a much stronger reducer than the ground state complex, eg the standard oxidation potential of the [Fe(bpy)3]2+ complex is 1.05 V in the ground state and 

Among transition metal complexes the iron compounds are those for which LMCT photochemistry is of crucial environmental relevance [51, 61, 62], Their photoreductions yield the Fe11 species and ligand radicals (L ), eg  

One of the most important effects is generation of OH radicals from the hydroxo complexes of Fem the reaction is the basis of the so-called photo-Fenton processes [63-78] (for details see Chapter 21). 

The radial charge redistribution caused by MLCT excitation outside the central atom can be effective in its oxidation and reduction of the ligand or even an external solvent molecule. These reaction modes are observed in complexes of metals at their low oxidation numbers (eg Cu1, Au1, Fe11, Ru11, MoIV) with relatively good 7r-acceptor ligands, eg CN, NCS, NO+, 0, pyridine, bipyridine, 1,10-phenanthroline, methylene blue) [48,53,79]. Often the final product is really not the oxidized, but only the substituted complex, eg  

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