The complex [{Ru(bipy)2}3(µ3-L)]3+ (H6L = hexahydroxytriphenylene), in which the tris-dioxolene bridging ligand is formally in the tris-semiquinone oxidation state [sq,sq,sq], undergoes three reversible ligand-centred oxidations to the [q,q,q] state (q = quinone); it exhibits very strong NIR absorption arising from Ru → L charge transfer whose maximum wavelength may be tuned over a wide range according to oxidation state.
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Barthram et al. (1998) studied this question.