Light-Controlled Switching of Perylene Bisimide Assemblies.

Light-driven changes in supramolecular interactions in perylene bisimides (PBIs) with pendant sulfur-containing functional groups at the bay position are demonstrated. In the ground state, a noncovalent S···X interaction between the σ-hole on sulfur and a heteroatom, X (X = O, N, S), of a neighboring molecule is the main driving force for intermolecular interactions, while in the excited state it is the π-π interaction between PBI scaffolds which drives assembly. The presence of heteroatoms in the solvent results in acceleration of the π-stacking process via the formation of a PBI-solvent complex. The excited-state dynamics involved in the assembly process were revealed via time-resolved fluorescence and transient absorption spectroscopies, while steady-state spectroscopy was used to evaluate the structure of the supramolecular assembly.

Highly Stable Red-Light-Emitting Electrochemical Cells.

The synthesis and characterization of a series of new cyclometalated iridium(III) complexes [Ir(ppy)2(N∧N)][PF6] in which Hppy = 2-phenylpyridine and N∧N is (pyridin-2-yl)benzo[d]thiazole (L1), 2-(4-(tert-butyl)pyridin-2-yl)benzo[d]thiazole (L2), 2-(6-phenylpyridin-2-yl)benzo[d]thiazole (L3), 2-(4-(tert-butyl)-6-phenylpyridin-2-yl)benzo[d]thiazole (L4), 2,6-bis(benzo[d]thiazol-2-yl)pyridine (L5), 2-(pyridin-2-yl)benzo[d]oxazole (L6), or 2,2'-dibenzo[d]thiazole (L7) are reported. The single crystal structures of [Ir(ppy)2(L1)][PF6]·1.5CH2Cl2, [Ir(ppy)2(L6)][PF6]·CH2Cl2, and [Ir(ppy)2(L7)][PF6] have been determined. The new complexes are efficient red emitters and have been used in the active layers in light-emitting electrochemical cells (LECs). The effects of modifications of the 2-(pyridin-2-yl)benzo[d]thiazole ligand on the photoluminescence and LEC performance have been examined. Extremely stable red-emitting LECs are obtained, and when [Ir(ppy)2(L1)][PF6], [Ir(ppy)2(L2)][PF6], or [Ir(ppy)2(L3)][PF6] are used in the active layer, device lifetimes greater than 1000, 6000, and 4000 h, respectively, are observed.

Regioisomerism in cationic sulfonyl-substituted [Ir(C

A series of regioisomeric cationic iridium complexes of the type [Ir(C^N)2(bpy)][PF6] (bpy = 2,2'-bipyridine) is reported. The complexes contain 2-phenylpyridine-based cyclometallating ligands with a methylsulfonyl group in either the 3-, 4- or 5-position of the phenyl ring. All the complexes have been fully characterized, including their crystal structures. In acetonitrile solution, all the compounds are green emitters with emission maxima between 493 and 517 nm. Whereas substitution meta to the Ir-C bond leads to vibrationally structured emission profiles and photoluminescence quantum yields of 74 and 77%, placing a sulfone substituent in a para position results in a broad, featureless emission band, an enhanced quantum yield of 92% and a shorter excited-state lifetime. These results suggest a larger ligand-centred ((3)LC) character of the emissive triplet state in the case of meta substitution and a more pronounced charge transfer (CT) character in the case of para substitution. Going from solution to the solid state (powder samples and thin films), the emission maxima are red-shifted for all the complexes, resulting in green-yellow emission. Data obtained from electrochemical measurements and density functional theory calculations parallel the photophysical trends. Light-emitting electrochemical cells (LECs) based on the complexes were fabricated and evaluated. A maximum efficiency of 4.5 lm W(-1) at a maximum luminance of 940 cd m(-2) was observed for the LEC with the complex incorporating the sulfone substituent in the 4-position when operated under pulsed current driving conditions.

Sticking and patching: tuning and anchoring cyclometallated ruthenium(II) complexes.

A series of [Ru(bpy)2(C^N)][PF6] (HC^N = 2-phenylpyridine derivative) complexes functionalized in the cyclometallating C^N phenyl ring with F, Me, OMe, CO2Me, S(t)Bu, SO2Me (ligands H1-H6) or in the C^N pyridine ring with 4-CO2Me or 4-C6H4P(O)(OEt)2 substituents (ligands H7 or H9) have been prepared and characterized; representative crystal structures confirm the structural features of the complexes. When the C^N ligand contains a CO2H substituent (ligand H28), deprotonation in addition to cyclometallation occurs to give a neutral, zwitter-ionic complex [Ru(bpy)2(8)]. The synthesis of the cationic complexes requires addition of a silver(i) salt (AgPF6 or AgBF4) to abstract Cl(-) from cis-[Ru(bpy)2Cl2] and (1)H NMR spectroscopic data are consistent with interactions between Ag(+) and the coordinated C^N ligand in [Ru(bpy)2(C^N)](+). The absorption spectra of [Ru(bpy)2(C^N)][PF6] (C^N = 1-6) are similar, but the introduction of the anchoring domains in [Ru(bpy)2(C^N)][PF6] with C^N = 7 or 9 enhances the absorption response; the greatest influence is observed in [Ru(bpy)2(9)](+) with the introduction of the 4-C6H4P(O)(OEt)2 substituent. Trends in emission and electrochemical behaviours of the complexes are interpreted in terms of the influence of the electronic properties of the C^N ligand substituents on the energies of the HOMO which is localized on the C^N ligand and Ru centre. This study provides an optimized synthetic route to the phosphonate ester derivative [Ru(bpy)2(9)][PF6], designed to anchor to a semiconductor surface; this complex also exhibits the most favourable absorption properties among the complexes studied.

Green-emitting iridium(III) complexes containing sulfanyl- or 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-(t)butylsulfanylphenyl)pyridine (H4), 2-(4-(t)butylsulfonylphenyl)pyridine (H5), 2-(4-(n)dodecylsulfanylphenyl)pyridine (H6), 2-(4-(n)dodecylsulfonylphenyl)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 (λ(em)(max) 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 (λ(em)(max) = 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 λ(em)(max) 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.

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].