Excited States in Strongly Coupled Bimetallic Ruthenium Polypyridines

OVIEDO, PAOLA S.; ARAMBURU TROSELJ, BRUNO M.; CADRANEL, ALEJANDRO; BARALDO VICTORICA, LUIS MARIO

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Simposio; 6th International Conference from Nanoparticles and Nanomaterials to Nanodevices and Nanosystems; 2019

We have examined the excited state dynamics of a family of cyanide-bridged bimetallic Ru(II),Ru(II) polypyridines using ultrafast vis-NIR transient absorption spectroscopy. All these complexes show the presence of an excited state which exhibit intense photoinduced absorptions in the NIR. We assign these transitions as a photoinduced intervalence charge transfer (PIIVCT) transitions like the one observed in the ground state of the mixed-valence form of these complexes. The energy and shape of the transitions observed for this state indicates that the vacant orbital runs parallel to the bridge and is substantially delocalized between both metallic ions. We label this state as 3MLCTz. Notable is that the lifetime of this state varies widely depending of the coordination sphere on the ruthenium ions. This is due to the presence of two other excited states that lack any photoinduced absorption in the NIR. For both states we assign a localized configuration with the hole perpendicular to the cyanide-bridge precluding an intense PIIVCT. These states differ in the localization of the hole. In one is in the same ion as the radical anion (3MLCTxy) and in the other it lays in the remote Ru ion (3MLCTr).The lifetimes of the delocalized state depend strongly on the energy order between the states. In some systems, the delocalized state has a lifetime of only a few picoseconds, while for the [RuII(tpy)(bpy)(CN)RuII(py)4Cl]2+ complex (tpy = (2,2';6',2"-terpyridine, bpy = 2,2?-bipyridine, py = pyridine), the 3MLCTz state is the emissive state and have a longer lifetime than the related monometallic complexes.