Photoinduced Redox Reactions of Ions in Solution

These are photoinduced electron transfer reactions between two ions. The closed-shell ions then form free radicals which can be charged or neutral, these primary photochemical products being very reactive. One example of this process is the electron transfer between a uranyl cation and a nitrate anion 

The uranyl cation (closed shell, U022+) absorbs light in the visible (VIS) 

So far we have considered only an orbital diagram without reference to the spin of the electrons. This is however an important point for the photophysics of metal complexes, just as for organic molecules. 

Low-spin (L) and high-spin (H) electron configurations of the d orbitals of a metal centre A is the crystal field splitting 

The intraligand (L-L) transitions remain very similar to those of the free ligands and the corresponding absorption bands are therefore also similar both in wavelength and in intensity. 

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