Energy transfer quenching by metal complexes

Following the observation of sensitized Cr(III) emission upon excitation of Ru(bpy)32+ -chromophore in double salts, the energy transfer process (reaction 51) has been studied in detail as a means of probing the photophysics of Cr(III)-complexes  

In favourable cases, intermolecular energy transfer processes can be used to estimate excited state lifetimes. The energy transfer from the ligand field excited state of Rh(phen)3 + to Cr(CN)5 is exoergonic and adiabatic. By measuring the yield of sensitized Cr(III) emission as a function of the acceptor concentration, the Stem-Volmer constant for the energy transfer has been calculated to be 3000 M l. If the quenching is pictured to occured at diffusion controlled rate (k lOi M s i), this yields an estimate of 

The quenching of the phosphorescence of Cr(bpy)33+ by a number of ammine complexes of Co(III) has been shown [77] to take place by electronic energy transfer  

Oxygen as a Quencher Molecular oxygen is an efficient quencher of electronically excited states of inorganic complexes and organic molecules. The quenching of Ru(bpy)32+ by molecular oxygen is believed to occur via electron transfer pathway while that of Cr(bpy)33+ occurs via energy transfer  

For a number of polypyridine complexes of Cr(III), the quenching rate constant is lower than the diffusion controlled limit by 2-3 orders of magnitude and are lower than that of kq values obtained for organic triplet states. The (lAg)02 state has a lower energy (12900 cm ) as compared to that of Cr(LL)33+ (13700 cm l) for it to be a potential acceptor [78], though Brunschwig and Sutin suggest (iHg)02 likely acceptor 

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