Photophysical Properties of Bimetallic Cyanide-Bridged Ru(II) Polypyridines. Evidence of delocalization in the Excited State.

PAOLA OVIEDO; ALEJANDRO CADRANEL; JOSÉ HODAK; LUIS M. BARALDO

Santiago de Chile

Conferencia; I-APS meeting; 2016

We present the photophysical properties of a family of cyanide-bridged ruthenium polipyridines, [(bpy)(tpy)Ru(µ-CN)Ru(bpy)2L]2+/3+ (tpy = 2,2?;6?,2??-terpyridine; bpy = 2,2?-bipyridine; L= acetonitrile (1, Fig. 1), 4- Dimethylaminopyridine (2), thiocyanate (3) or chloride (4). For comparison, we also present the behavior of the complex [(bpy)(tpy)Ru(µ-CN)Ru(py)4(Cl)]2+. Near infrared Transient absorption spectra of these complexes reveal that the first populate state presents a band in the NIR that we assign as a metal to metal charge transfer (MMCT) transition and points to a mixed-valence character for this state (black and red spectra, Fig. 2). The energy of this transition shifts to the red when the chloride ligand is replaced by a L ligand with less donor character. By comparison with the properties of related mixed-valence complexes a delocalized nature can be assigned to the excited state of (4). It is interesting to note that for the ground state mixed-valence form of these complexes the complex (4) shows a localized character. This contrasting behavior reveals the role of the radical-anion ligand in the photoinduced state. For all complexes, the first populate state decays to the emissive state which does not present a transition in the NIR pointing to a different configuration for the latter (green spectra, Fig. 2).