Tuning oxyquinolate non-innocence at the ruthenium polypyridyl core

The electronic structure of [Ru(bpy)₂(OQN)]⁺ (where bpy = 2,2′-bipyridine and OQN = 8-oxyquinolate) has been revisited using a complimentary suite of theoretical (DFT/TD-DFT), electrochemical (cyclic voltammetry) and spectroscopic techniques (UV/Vis/NIR absorption, EPR spectroscopy). Through functionalization of the R-OQN ligand (R = 2-Me; 5,7-Me₂; 5-F; 5-Cl; 5,7-Cl₂; 5-NO₂) charge delocalization across the non-innocent ruthenium-oxyquinolate framework has been investigated and correlated with substituent Hammett parameters. Combined spectroscopic and computational studies indicate substantial mixing at the HOMO-3, HOMO and LUMO+2 levels between the Ru and R-OQN π-systems allowing controlled tuning of complex redox potentials while maintaining panchromatic absorption characteristics. UV/Vis/NIR and EPR spectroelectrochemical data is reported which shows strong evidence for substituent dependence of hole delocalization onto the R-OQN ligand following one-electron oxidation of the hybrid Ru(R-OQN) based HOMO level. EPR data correlates very well with Mulliken spin-density calculations confirming non-innocence of the R-OQN ligand which allows control of spin-distribution across the Ru(R-OQN) π-system Several [Ru(bpy)₂(R-OQN)]⁺ complexes show enhanced charge delocalization across the non-innocent ruthenium-oxyquinolate framework that correlates well with substituent Hammett parameters (R = 2-Me; 5,7-Me ₂; 5-F; 5-Cl; 5,7-Cl₂; 5-NO₂). Control of hole delocalization onto R-OQN ligands is demonstrated following one-electron oxidation as probed by UV/Vis/NIR, EPR and spin-density investigations.