Ruthenium Charge Transfer Light Absorbers

Ruthenium and osmium polyazine complexes have been widely used as light absorbers. The complex [Ru(bpy)3] (Fig. 2) is a well studied LA with high extinction coefficients in the ultraviolet and visible regions of the spectrum. This complex shows intense absorptions in the UV region that are intraligand n- n (IL) and in the visible region that are MLCT transitions. Upon optical excitation at 450 nm, population of the Ru(d7i)- bpy(ji ) MLCT occurs. 

The quantum yield, O, for an excited state process is given by the ratio of the rate constants for the process of interest, divided by the sum of all the rate constants for the deactivation of a state for a directly populated state. For an indirectly populated state, this ratio is multiplied by the fraction of light that populates this state, Eq. (12). For emission from the MLCT state of [Ru(bpy)3] in the absence of a quencher, is  

FIGURE 5. Jablonski diagram for [Ru(tpy)2] (tpy = 2,2 6, 2 -terpyridine GS = ground state MLCT = metal-to-ligand charge-transfer kr = rate constant for radiative decay k r = rate constant for non-radiative decay k sc = rate constant for intersystem crossing). 

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