Sweetness and light: Sugar-functionalized C^N and N^N ligands in [Ir(C^N)2(N^N)]Cl complexes

Sugars represent a readily available entry into the chiral pool and possess a multivalent functionality allowing specific functionalzation for attachment to scaffolds possessing programmed properties. We report a series of cyclometallated iridium(III) complexes [Ir(C^N) 2 (N^N)][PF 6 ] in which a photo- and redox-active iridium scaffold is functionalized with ribofuranose substituents. The localization of HOMO and LUMO character in different parts of the iridium core is retained in the conjugates and proof-of-concept compounds with the ribofuranose attached to the C^N and N^N ligands confirm that the photophysical and redox properties may be refined utilizing the well-established algorithms

Regioisomerism in cationic sulfonyl-substituted [Ir(C^N)2(N^N)]+ complexes: its influence on photophysical properties and LEC performance

In a series of regioisomeric [Ir(C^N) 2 (bpy)] + complexes containing methylsulfonyl groups on the cyclometallating ligands, the influence of the substitution position on photophysical, electrochemical and LEC device properties is investigated

Modular synthesis of simple cycloruthenated complexes with state-of-the-art performance in p-type DSCs

A modular approach based on Suzuki-Miyaura cross coupling and Miyaura borylation has been used to prepare two cyclometallated [Ru(N^N) 2 (C^N)] + complexes which possess either a carboxylic or phosphonic acid group attached via a phenylene spacer to the 4-position of the pyridine ring in the C^N ligand. The key intermediate in the synthetic pathway is [Ru(bpy) 2 ( 1 )] + where bpy = 2,2'-bipyridine and H 1 is 4-chloro-2-phenylpyridine. The crystal structure of [Ru(bpy) 2 ( 1 )][PF 6 ] is presented. Reaction of [Ru(bpy) 2 ( 1 )][PF 6 ] with 4-carboxyphenylboronic acid leads to [Ru(bpy) 2 (H 6 )][PF 6 ], while the phosphonic acid analogue is isolated as the zwitterion [Ru(bpy) 2 (H 5 )]. The cyclometallated complexes have been characterized by mass spectrometry, multinuclear NMR spectroscopy, absorption spectroscopy and electrochemistry. [Ru(bpy) 2 ( 5 )] adsorbs onto NiO FTO/NiO electrodes (confirmed by solid-state absorption spectroscopy) and its performance in p-type dye-sensitized solar cells (DSCs) has been compared to that of the standard dye P1; two-screen printed layers of NiO give better DSC performances than one layer. Duplicate DSCs containing [Ru(bpy) 2 (H 5 )] achieve short-circuit current densities ( J SC ) of 3.38 and 3.34 mA cm –2 and photoconversion efficiencies ( η ) of 0.116 and 0.109%, respectively, compared to values of J SC = 1.84 and 1.96 mA cm –2 and η = 0.057 and 0.051% for P1. Despite its simple dye structure, the performance of [Ru(bpy) 2 (H 5 )] parallels the best-performing cyclometallated ruthenium(II) dye in p-type DSCs reported previously (He et al , J. Phys. Chem. C , 2014, 118 , 16518) and confirms the effectiveness of a phosphonic acid anchor in the dye and the attachment of the anchoring unit to the pyridine (rather than phenyl) ring of the cyclometallating ligan

Chloride ion impact on materials for light-emitting electrochemical cells

Small quantities of Cl(-) ions result in dramatic reductions in the performance of ionic transition metal complexes in light-emitting electrochemical cells. Strong ion-pairing between aromatic protons and chloride has been established in both the solid state and solution. X-ray structural determination of 2{[Ir(ppy)2(bpy)][Cl]}·2CH2Cl2·[H3O]·Cl reveals the unusual nature of an impurity encountered in the preparation of [Ir(ppy)2(bpy)][PF6]

Exploring the effect of the cyclometallating ligand in 2-(pyridine-2-yl)benzo[d]thiazole-containing iridium(III) complexes for stable light-emitting electrochemical cells

The preparation and characterization of a series of iridium(III) ionic transition-metal complexes for application in light-emitting electrochemical cells (LECs) are reported. The complexes are of the type [Ir(C^N) 2 (N^N)][PF 6 ] in which C^N is one of the cyclometallating ligands 2-(3-( tert -butyl)phenyl)pyridine (tppy), 2-phenylbenzo[ d ]thiazole (pbtz), 1-phenyl-1 H -pyrazole (ppz) and 1-phenylisoquninoline (piq), and N^N is 2-(pyridine-2-yl)benzo[ d ]thiazole (btzpy). The variation in the C^N ligands allows the HOMO energy level to be tuned, leading to HOMO−LUMO gaps in the range 2.76‒3.01 eV and values of of 0.81‒1.11 V. In solution, the complexes are orange to deep-red emitters ( λ max in the range 600-660 nm), with quantum yields between 2% for [Ir(tppy) 2 (btzpy)][PF 6 ] to 41% for [Ir(pbtz) 2 (btzpy)][PF 6 ]. Similar trends for the emission maxima and photoluminescence quantum yields are observed in the solid state. Density functional theory (DFT) calculations support the charge transfer nature of the emission. Very bright electroluminescence was observed for LECs containing [Ir(pbtz) 2 (btzpy)][PF 6 ], although the device was not stable under continuous operation; this is attributed to an unbalanced charge distribution and/or to a fast ionic migration. Significantly, LECs fabricated with [Ir(tppy) 2 (btzpy)][PF 6 ] in the active layer are very stable, produce pure red emission and show no signs of degradation over a period of 5 days of continuous operation

4'-Functionalized 2,2':6',2''-terpyridines as the N^N domain in [Ir(C^N)2(N^N)][PF6] complexes

The cyclometallated iridium(III) complexes [Ir(ppy)2(NˆN)][PF6] (Hppy = 2-phenylpyridine) with NˆN = 4′-chloro-2,2′:6′,2″-terpyridine (1), 4′-methoxy-2,2′:6′,2″-terpyridine (2), 4′-ethoxy-2,2′:6′,2″-terpyridine (3), 4′-methylthio-2,2′:6′,2″-terpyridine (4), 4′-phenylthio-2,2′:6′,2″-terpyridine (5) and 4′-dimethylamino-2,2′:6′,2″-terpyridine (6) are reported including the single crystal structures of 2{[Ir(ppy)2(1)][PF6]}·0.6Et2O·CH2Cl2, [Ir(ppy)2(5)][PF6]·0.5CH2Cl2 and [Ir(ppy)2(6)][PF6]. The single crystal structure of [Ir(ppy)2(3)]Cl·2H2O·MeCN is also reported. In each complex, the 2,2′:6′,2″-terpyridine (tpy) ligand binds to the metal centre in a bidentate fashion with the non-coordinated pyridine ring folded into the coordination sphere and engaging in a pyridine–phenyl π-stacking interaction. Solution NMR spectra are consistent with hindered rotation of the non-coordinated pyridine ring at 298 K, with intra-cation CH…N(pyridine) hydrogen bond formation between adjacent [ppy]– and tpy ligands. Trends in the electrochemical HOMO–LUMO gaps and emission maxima of the complexes (in CH2Cl2 solution) are consistent with the electron-withdrawing or releasing properties of the 4′-tpy substituent; in degassed solution, [Ir(ppy)2(6)][PF6] has a quantum yield of 24.8% and emission lifetime of 441 ns, while the other complexes exhibit significantly lower quantum yields and shorter lifetimes

Green-emitting iridium(III) complexes containing sulfone-functionalized cyclometallating 2-phenylpyridine ligands

A series of [Ir(C^N)2(bpy)][PF6] complexes in which the cyclometallating ligands contain fluoro, sulfane or sulfone groups is reported. The conjugate acids of the C^N ligands in the complexes are 2-(4-fluorophenyl)pyridine (H1), 2-(4-methylsulfonylphenyl)pyridine (H3), 2-(4-tbutylsulfanylphenyl)pyridine (H4), 2-(4-tbutylsulfonylphenyl)pyridine (H5), 2-(4-ndodecylsulfanylphenyl)pyridine (H6), 2-(4-ndodecylsulfonylphenyl)pyridine (H7). The single crystal structures of H3 and H5 are described. [Ir(C^N)2(bpy)][PF6] with C^N = 1, 3, 4, 5 and 7 were prepared from the appropriate [Ir2(C^N)4Cl2] dimer and bpy; the structure of [Ir2(3)4Cl2]·2CH2Cl2 was determined. [Ir(6)2(bpy)][PF6] was prepared by nucleophilic substitution starting from [Ir(1)2(bpy)][PF6]. The [Ir(C^N)2(bpy)][PF6] complexes have been characterized by NMR, IR, absorption and emission spectroscopic and mass spectrometric methods. The single crystal structures of enantiomerically pure Δ-[Ir(1)2(bpy)][PF6] and of rac-4{[Ir(1)2(bpy)][PF6]}·Et2O·2CH2Cl2 are described, and the differences in inter-cation packing in the structures compared. [Ir(1)2(bpy)][PF6], [Ir(4)2(bpy)][PF6] and [Ir(6)2(bpy)][PF6] (fluoro and sulfane substituents) are yellow emitters (λmaxem between 557 and 577 nm), and the room temperature solution emission spectra are broad. The sulfone derivatives [Ir(3)2(bpy)][PF6], [Ir(5)2(bpy)][PF6] and [Ir(7)2(bpy)][PF6] are green emitters and the emission spectra are structured (λmaxem = 493 and 523 to 525 nm). High photoluminescence quantum yields (PLQYs) of 64–74% are observed for the sulfone complexes in degassed solutions. The emission lifetimes for the three complexes containing sulfone substituents are an order of magnitude longer (2.33 to 3.36 μs) than the remaining complexes (0.224 to 0.528 μs). Emission spectra of powdered solid samples have also been recorded; the broad emission bands have values of λmaxem in the range 532 to 558 nm, and PLQYs for the powdered compounds are substantially lower (≤23%) than in solution. Trends in the redox potentials for the [Ir(C^N)2(bpy)][PF6] complexes are in accord with the observed emission behaviour