Strongly Coupled Cyclometalated Ruthenium–Triarylamine Hybrids: Tuning Electrochemical Properties, Intervalence Charge Transfer, and Spin Distribution by Substituent Effects

Abstract

Nine cyclometalated ruthenium complexes with a redox-active diphenylamine unit in the para position to the RuC bond were prepared. MeO, Me, and Cl substituents on the diphenylamine unit and three types of auxiliary ligands-bis(N-methylbenzimidazolyl)pyridine (Mebip), 2,2':6',2''-terpyridine (tpy), and trimethyl-4,4',4''-tricarboxylate-2,2':6',2''-terpyridine (Me3 tctpy)--were used to vary the electronic properties of these complexes. The derivative with an MeO-substituted amine unit and Me3 tctpy ligand was studied by single-crystal X-ray analysis. All complexes display two well-separated redox waves in the potential region of +0.1 to +1.0 V versus Ag/AgCl, and the potential splitting ranges from 360 to 510 mV. Spectroelectrochemical measurements show that these complexes display electrochromism at low potentials and intense near-infrared (NIR) absorptions. In the one-electron oxidized form, the complex with the Cl-substituted amine unit and Mebip ligand shows a moderate ligand-to-metal charge transfer at 800 nm. The other eight complexes show asymmetric, narrow, and intense intervalence charge-transfer transitions in the NIR region, which are independent of the polarity of the solvent. The Mebip-containing complexes display rhombic or broad isotropic EPR signals, whereas the other seven complexes show relatively narrow isotropic EPR signals. In addition, DFT and time-dependent DFT studies were performed to gain insights into the spin distributions and NIR absorptions.

Excited state decay of cyclometalated polypyridine ruthenium complexes: insight from theory and experiment

“…16,17,19,[107][108][109] Additionally, cyclometalated bridging ligands enhance the electronic coupling between the redox centers in mixed-valent Ru/Ru complexes [110][111][112] and Ru/organic hybrid structures. [113][114][115][116] Despite the large variety of cyclometalated polypyridine ruthenium complexes synthesized up-to-date, however, no phosphorescence comparable to [Ru(bpy) 3 ] 2+ has yet been achieved. Furthermore, a general explanation for the striking difference in the luminescence Her key research interests comprise functional complex systems based on coordination and organometallic compounds with special emphasis on molecular wires, light-harvesting systems, bistable systems, emitters, switches and sensors as well as on (biomimetic) catalysts.…”

Strongly Coupled Cyclometalated Ruthenium Triarylamine Chromophores as Sensitizers for DSSCs

“…The 5‐substituted 1,3‐di‐(2‐pyridyl)benzene ligands L a (R=N(4‐C 6 H 4 OMe) 2 ), L b (R=N(C 6 H 5 ) 2 ) and L c (R= N ‐carbazolyl) were synthesized starting from the previously reported 1‐bromo‐3,5‐di‐(2‐pyridyl)benzene under Buchwald–Hartwig cross‐coupling reaction conditions similar to a method we, as well Zhong and co‐workers employed previously . In the present study, the dimeric palladium(II) precatalyst bis(μ‐mesylate)bis[(2‐(2′‐aminophenyl‐κ N )phenyl‐κ C 1 )palladium(II)] [Pd] 2 was used along with the phosphane ligand 2‐dicyclohexylphosphano‐2′,6′‐diisopropoxybiphenyl to provide a catalytically competent catalyst that afforded the ligands in yields of 82–98 %.…”

Transition from a Metal‐Localized Mixed‐Valence Compound to a Fully Delocalized and Bridge‐Biased Electrophore in a Ruthenium–Amine–Ruthenium Tricenter System

“…Such a connection mode ensures strong electronic coupling between the ruthenium and amine components. [24,25] …”

“…The above transition from a metal-localized mixed-valence compound to a delocalized electrophore with varied spin density distribution can be understood by comparing the amine oxidation potential of the mono-substituted triarylamines 15-18 [28] and the Ru III/II potential of the monoruthenium complexes 19(PF 6 )-21(PF 6 ) [25] with a different NNN auxiliary ligand ( Figure 5). Complex 19(PF 6 ) with Mebip has a much lower Ru III/II potential with respect to the amine oxidation potential of 15-17 with NO 2 , Cl, or Me substituents.…”

“…Each ruthenium component contains a RuÀC bond, which makes the Ru III/II potential comparable to the amine oxidation potential. [24,25] The bridging amine nitrogen atom is placed on the para position of the metalating phenyl ring with respect to the RuÀC bond. Such a connection mode ensures strong electronic coupling between the ruthenium and amine components.…”