title: Probing the Noninnocent π-Bonding Influence of N-Carboxyamidoquinolate Ligands on the Light Harvesting and Redox Properties of Ruthenium Polypyridyl Complexes.
abstract: Electronic and photophysical characterization is presented for a series of bis-heteroleptic [Ru(bpy)2(R-CAQN)](+) complexes where CAQN is a bidentate N-(carboxyaryl)amidoquinolate ligand and the aryl substituent R = p-tolyl, p-fluorobenzene, p-trifluoromethylbenzene, 3,5-bis(trifluoromethyl)benzene, or 4-methoxy-2,3,5,6-tetrafluorobenzene. Characterized by a strong noninnocent Ru(dπ)-CAQN(π) bonding interaction, density functional theory (DFT) analysis is used to estimate the contribution of both atomic Ru(dπ) and ligand CAQN(π) manifolds to the frontier molecular orbitals of these complexes. UV-vis absorption and emission studies are presented where the noninnocent Ru(dπ)-CAQN(π) bonding scheme plays a major role in defining complex electronic and photophysical properties. Oxidation potentials are tuned over a range of 0.92 V with respect to the [Ru(bpy)3](2+) reference system, hereafter referred to as 1(2+), by varying the degree of R-CAQN fluorination while maintaining consistently strong and panchromatic visible absorption properties. Electron paramagnetic resonance (EPR) spectroscopy is employed to experimentally map delocalization of the unpaired electron/electron-hole within the delocalized Ru(dπ)-CAQN(π) singly occupied valence molecular orbital of the one-electron oxidized complexes. EPR data is complemented experimentally by UV-vis-NIR spectroelectrochemistry, and computationally by molecular orbital Mulliken contributions and spin-density analysis. It is ultimately demonstrated that the CAQN ligand framework provides a simple yet broad synthetic platform in the design of redox-active transition metal chromophores with a range of electronic and spectroscopic characteristics hinting at the diversity and potential of these complexes toward photochemical and catalytic applications.
authors.affiliation: Department of Chemistry, University of Massachusetts Boston , 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States.
authors.forename: Ken T
authors.initials: KT
authors.lastname: Ngo
authors.affiliation: Department of Chemistry, University of Massachusetts Boston , 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Lee
authors.affiliation: Department of Chemistry, University of Massachusetts Boston , 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States.
authors.forename: Sashari D
authors.initials: SD
authors.lastname: Pinnace
authors.affiliation: Chemistry Department, Baruch College , New York, New York 10010, United States.
authors.forename: David J
authors.initials: DJ
authors.lastname: Szalda
authors.affiliation: EPR Division, Bruker BioSpin Corporation , 44 Manning Road, Billerica, Massachusetts 01821, United States.
authors.forename: Ralph T
authors.initials: RT
authors.lastname: Weber
authors.affiliation: Department of Chemistry, University of Massachusetts Boston , 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Rochford