Abstract
Complexes Ru(bpy-R)2(NCS)2, where R = H (1), 4,4'-(CO2Et)2 (2), 4,4'-(OMe)2 (3), and 4,4'-Me2 (4), were studied by spectroelectrochem. in the UV-visible and IR regions and by in situ EPR. The exptl. information obtained for the frontier orbitals as supported and ascertained by d. functional theory calcns. for 1 is relevant for the productive excited state. In addn. to the parent 1, the ester complex 2 was chosen for its relationship to the carboxylate species involved for binding to TiO2 in solar cells; the donor-substituted 3 and 4 allowed for better access to oxidized forms. Reflecting the metal-to-ligand (Ru $\rightarrow$ bpy) charge-transfer characteristics of the compds., the electrochem. and EPR results for compds. 1-4 agree with previous notions of one metal-centered oxidn. and several (bpy-R) ligand-centered redns. The first one-electron redn. produces extensive IR absorption, including intraligand transitions and broad ligand-to-ligand intervalence charge-transfer transitions between the one-electron-reduced and unreduced bpy-R ligands. The electron addn. to one remote bpy-R ligand does not significantly affect the N-C stretching frequency of the RuIINCS unit. Upon oxidn. of RuII to RuIII, however, the single N-C stretching band exhibits a splitting and a shift to lower energies. The d. functional theory calcns. serve to reproduce and understand these effects; they also suggest significant spin d. on S for the oxidized form. on SciFinder(R)
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