Tuning Oxyquinolate Non‐Innocence at the Ruthenium Polypyridyl Core

Abstract

Abstract 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‐Me 2 ; 5‐F; 5‐Cl; 5,7‐Cl 2 ; 5‐NO 2 ) 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