Solvation State of the Metal Ion

Although detrimental to the emission intensity, vibrational quenching allows one to assess the number of water molecules q interacting in the inner-coordination sphere. Several phenomenological equations have been proposed, based on the assumptions that 0-D oscillators contribute little to deactivation and that all the other deactivation paths are the same in water and in deuterated water and can henceforth be determined by measuring the lifetime in the deuterated solvent. An important point for their application is to make sure that quenching by solvent vibrations is by far the most important deactivation process in the molecule. If other temperature-dependent phenomena (e.g., phonon-assisted back transfer) are operating, these relationships become unreliable. This has often been observed with Tb [27]. 

Altogether, such relationships, which exist for Nd , Sm Eu , Tb , Dy, and Yb, are to be used with care and bearing in mind their peculiar calibration. The general form of these relationships is  

A flaw to avoid is to use (33)-(37) with tobs(D20) set equal to the observed lifetime measured on the hydrated sample at 77 K because it is not granted that all vibrational quenching is switched off at this temperature. 

Equations calibrated with polyaminocarboxylates and relying on the sole determination of t(H20) have also been suggested, but they are less reliable  

Establishing q for is really problematic and other relationships have been put forward, which do not yield very satisfying results, owing to too limited calibration range, as, by the way, for (38)-(40). 

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