title: Effect of ligands with extended π-system on the photophysical properties of Ru(II) complexes.
abstract: Density functional theory calculations were performed on a series of six ruthenium complexes possessing tridentate ligands: [Ru(tpy)(2)](2+) (1; tpy = [2,2';6',2'']-terpyridine), [Ru(tpy)(pydppx)](2+) (2; pydppx = 3-(pyrid-2'-yl)-11,12-dimethyldipyrido[3,2-a: 2',3'-c]phenazine), [Ru(pydppx)(2)](2+) (3), [Ru(tpy)(pydppn)](2+) (4; pydppn = 3-(pyrid-2'-yl)-4,5,9,16-tetraazadibenzo[a,c]naphthacene), [Ru(pydppn)(2)](2+) (5), and [Ru(tpy)(pydbn)](+) (6; pyHdbn = 3-pyrid-2'-yl-4,9,16-triazadibenzo[a,c]naphthacene). The calculations were compared to experimental data, including electrochemistry and electronic absorption spectra. The theoretical results reveal that the lowest-lying singlet and triplet states in 4 and 5 are pydppn-based ππ* in character, which are remarkably different from the lowest-lying metal-to-ligand charge transfer (MLCT) states in 1-3. The calculated lowest triplet states in 4 and 5 are consistent with the (3)ππ* states observed experimentally. However, although the extended π-system of pydbn(-) is similar to that of pydppn, the HOMO of 6 lies above those of 4 and 5, resulting in strikingly different spectroscopic properties. Calculations show that the lowest triplet excited state of 6 is a combination of (3)MLCT and (3)ππ*. This work demonstrates that the electronic structure of the tridentate ligand has a pronounced effect on the photophysical properties of ruthenium(II) complexes and that DFT and TD-DFT methods are a useful tool that can be used to predict photophysical and redox properties of transition metal complexes.
authors.affiliation: Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Yujie
authors.initials: Y
authors.lastname: Sun
authors.forename: Maya
authors.initials: M
authors.lastname: El Ojaimi
authors.forename: Richard
authors.initials: R
authors.lastname: Hammitt
authors.forename: Randolph P
authors.initials: RP
authors.lastname: Thummel
authors.forename: Claudia
authors.initials: C
authors.lastname: Turro
mesh_terms: D000042:Absorption; D004563:Electrochemistry; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory; D012428:Ruthenium / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D012428:Ruthenium