Highly Stable and Efficient Light-Emitting Electrochemical Cells Based on Cationic Iridium Complexes Bearing Arylazole Ancillary Ligands

Experimental and theoretical studies of pH-responsive iridium(III) complexes of azole and N-heterocyclic carbene ligands

A series of nine luminescent iridium(III) complexes with pH-responsive imidazole and benzimidazole ligands have been prepared and characterized. The first series of complexes were of the form [Ir(ppy)2(N^N)]+ or [Ir(ppy)2(C^N)]+ (where ppy is 2-phenylpyridine and N^N is 2-(2-pyridyl)imidazole or 2-(2-pyridyl)benzimidazole and C^N represents a pyridyl-triazolylidene-based N-heterocyclic carbene ligand). For these complexes, the benzimidazole group was either unsubstituted or substituted with electron-withdrawing (Cl) or electron-donating (Me) groups. The second series of complexes were of the form [Ir(phbim)2(N^N)]+ or [Ir(phbim)2(C^N)]+ (where phbim is 2-phenylbenzimidazole and N^N is either 2,2'-bipyridine or 1,10-phenanthroline and C^N is either a pyridyl-imidazolylidene or pyridyl-triazolylidene N-heterocyclic carbene ligand). UV-visible and photoluminescence pH titration studies showed that changing the protonation state of these complexes results in significant changes in the photoluminescence emission properties. The pKa values of prepared complexes were estimated from the spectroscopic pH titration data and these values show that the nature of the pH-sensitive ligands (either main or ancillary ligands) resulted in a significant capacity to modulate the pKa values for these compounds with values ranging from 5.19-11.22. Theoretical investigations into the nature of the electronic transitions for the different protonation states of compounds were performed and the results were consistent with the experimental results.

Neutral 2-phenylbenzimidazole-based iridium(III) complexes with picolinate ancillary ligand: tuning the emission properties by manipulating the substituent on the benzimidazole ring

We report the synthesis and characterization of ten neutral bisheteroleptic iridium(III) complexes with 2-phenylbenzimidazole cyclometallating ligand and picolinate as ancillary ligand. The 2-phenylbenzimidazole has been modified by selected substituents introduced on the cyclometallating ring and/or on the benzimidazole moiety. The integrity of the complexes has been assessed by NMR spectroscopy, by high-resolution mass spectrometry and by elemental analysis. The complexes are demonstrated to be highly phosphorescent at room temperature and a luminescence study with comprehensive ab initio calculations allow us to determine the lowest emitting excited state which depends on the substituent nature and its position on the cyclometallating ligand.

Phototoxicity of cyclometallated Ir(III) complexes bearing a thio-bis-benzimidazole ligand, and its monodentate analogue, as potential PDT photosensitisers in cancer cell killing

Two novel cyclometallated iridium(III) complexes have been prepared with one bidentate or two monodentate imidazole-based ligands, 1 and 2, respectively. The complexes showed intense emission with long lifetimes of the excited state. Femtosecond transient absorption experiments established the nature of the lowest excited state as 3IL state. Singlet oxygen generation with good yields (40% for 1 and 82% for 2) was established by detecting 1O2 directly, through its emission at 1270 nm. Photostability studies were also performed to assess the viability of the complexes as photosensitizers (PS) for photodynamic therapy (PDT). Complex 1 was selected as a good candidate to investigate light-activated killing of cells, whilst complex 2 was found to be toxic in the dark and unstable under light. Complex 1 demonstrated high phototoxicity indexes (PI) in the visible region, PI > 250 after irradiation at 405 nm and PI > 150 at 455 nm, in EJ bladder cancer cells.

Deep-blue light-emitting cationic iridium(III) complexes featuring diamine ancillary ligands: Experimental and theoretical investigations

Deep-blue emitters based on combining two approaches are reported here. In the first approach, the nitrogen content of the cyclometallated ligand is increased using 2,4'-bpy ligands, leading to a low highest occupied molecular orbital energy. In the second approach, 2,2'-bpy is replaced with a lower electron donating ligand, leading to a high lowest unoccupied molecular orbital (LUMO) energy. Thus, three new ionic transition metal complexes of [Ir(2,4'-bpy)2(NN)]PF6 [where NN is 2,2'-bpy (1), o-phenylenediamine (2), and 4-methoxy-o-phenylenediamine (3)] were synthesized, and their electronic and photophysical features were studied. In solution, [Ir(2,4'-bpy)2bpy]PF6 emits blue light centered at 396 nm, which is blue-shifted compared to [Ir(ppy)2bpy]PF6. The low electron donation of the diamine ancillary ligands introduces the contribution of the cyclometallated ligand to the LUMO, changing the nature of the emission and leading to different photophysical features. Density functional theory calculations indicate the long bond distances of Ir-Ns at the diamine ligands, suggesting weak metal-ligand interactions and low quantum yields.1.

Tunable Emissive Ir(III) Benzimidazole-quinoline Hybrids as Promising Theranostic Lead Compounds

Bioactive and luminescent cyclometallated Ir(III) complexes [Ir(ppy)₂ L1]Cl (1) and [Ir(ppy)₂ L2]Cl (2) containing a benzimidazole derivative (L1/L2) as auxiliary mimic of a nucleotide have been synthesised. The emissive properties of both complexes are conditioned by the nature of L1 and L2, rendering an orange and a green emitter respectively. Both are highly emissive with quantum yield increasing in absence of oxygen up to 0.26 (1) and 0.36 (2), suggesting their phosphorescent character. Antiproliferative activity against lung cancer A549 cells increased up to 15 times upon irradiation conditions, reaching IC₅₀ values in the nanomolar range (0.3±0.09 μM (1) and 0.26±0.14 μM (2)) and pointing them as good PSs candidates for photodynamic therapy via ¹ O₂ generation. Cellular biodistribution analysis by fluorescence microscopy suggest the lysosomes as the preferential accumulation organelle. Time-resolved studies showed a greatly increased cellular emission lifetime compared to the solution values, indicating binding to macromolecules or cellular structures and restriction of collision and vibrational quenching.

Rational Design of Mono- and Bi-Nuclear Cyclometalated Ir(III) Complexes Containing Di-Pyridylamine Motifs: Synthesis, Structure, and Luminescent Properties

Heteroleptic cyclometalated iridium (III) complexes (1–3) containing di-pyridylamine motifs were prepared in a stepwise fashion. The presence of the di-pyridylamine ligands tunes their electronic and optical properties, generating blue phosphorescent emitters at room temperature. Herein we describe the synthesis of the mononuclear iridium complexes [Ir(ppy)₂(DPA)][OTf] (1), (ppy = phenylpyridine; DPA = Dipyridylamine) and [Ir(ppy)₂(DPA-PhI)][OTf] (2), (DPA-PhI = Dipyridylamino-phenyliodide). Moreover, the dinuclear iridium complex [Ir(ppy)₂(L)Ir(ppy)₂][OTf]₂ (3) containing a rigid angular ligand “L = 3,5-bis[4-(2,2′-dipyridylamino)phenylacetylenyl]toluene” and displaying two di-pyridylamino groups was also prepared. For comparison purposes, the related dinuclear rhodium complex [Rh (ppy)₂(L)Rh(ppy)₂][OTf]₂ (4) was also synthesized. The x-ray molecular structure of complex 2 was reported and confirmed the formation of the target molecule. The rhodium complex 4 was found to be emissive only at low temperature; in contrast, all iridium complexes 1–3 were found to be phosphorescent in solution at 77 K and room temperature, displaying blue emissions in the range of 478–481 nm.

Simultaneous Probing of Metabolism and Oxygenation of Tumors In Vivo Using FLIM of NAD(P)H and PLIM of a New Polymeric Ir(III) Oxygen Sensor

Tumor cells are well adapted to grow in conditions of variable oxygen supply and hypoxia by switching between different metabolic pathways. However, the regulatory effect of oxygen on metabolism and its contribution to the metabolic heterogeneity of tumors have not been fully explored. In this study, we develop a methodology for the simultaneous analysis of cellular metabolic status, using the fluorescence lifetime imaging microscopy (FLIM) of metabolic cofactor NAD(P)H, and oxygen level, using the phosphorescence lifetime imaging (PLIM) of a new polymeric Ir(III)-based sensor (PIr3) in tumors in vivo. The sensor, derived from a polynorbornene and cyclometalated iridium(III) complex, exhibits the oxygen-dependent quenching of phosphorescence with a 40% longer lifetime in degassed compared to aerated solutions. In vitro, hypoxia resulted in a correlative increase in PIr3 phosphorescence lifetime and free (glycolytic) NAD(P)H fraction in cells. In vivo, mouse tumors demonstrated a high degree of cellular-level heterogeneity of both metabolic and oxygen states, and a lower dependence of metabolism on oxygen than cells in vitro. The small tumors were hypoxic, while the advanced tumors contained areas of normoxia and hypoxia, which was consistent with the pimonidazole assay and angiographic imaging. Dual FLIM/PLIM metabolic/oxygen imaging will be valuable in preclinical investigations into the effects of hypoxia on metabolic aspects of tumor progression and treatment response.

Crystal structure of 2-(1H-pyrazol-3-yl-κN)pyridine-κN-bis(2-(2,4-difluorophenyl)pyridinato-κ 2 C,N)iridium(III) sesquihydrate, C30H18F4IrN5·1.5[H2O]

C30H18F4IrN5·1.5[H2O], tetragonal, I41/a (no. 88), a = 37.5562(5) Å, b = 37.5562(5) Å, c = 9.2031(2) Å, V = 12980.7(4) Å3, Z = 16, R gt (F) = 0.0312, wR ref(F 2) = 0.1166, T = 300(2) K.

Theoretical Approach for the Luminescent Properties of Ir(III) Complexes to Produce Red-Green-Blue LEC Devices

With an appropriate mixture of cyclometalating and ancillary ligands, based on simple structures (commercial or easily synthesized), it has been possible to design a family of eight new Ir(III) complexes (1A, 1B, 2B, 2C, 3B, 3C, 3D and 3E) useful as luminescent materials in LEC devices. These complexes involved the use of phenylpyridines or fluorophenylpyridines as cyclometalating ligands and bipyridine or phenanthroline-type structures as ancillary ligands. The emitting properties have been evaluated from a theoretical approach through Density Functional Theory and Time-Dependent Density Functional Theory calculations, determining geometric parameters, frontier orbital energies, absorption and emission energies, injection and transport parameters of holes and electrons, and parameters associated with the radiative and non-radiative decays. With these complexes it was possible to obtain a wide range of emission colours, from deep red to blue (701-440 nm). Considering all the calculated parameters between all the complexes, it was identified that 1B was the best red, 2B was the best green, and 3D was the best blue emitter. Thus, with the mixture of these complexes, a dual host-guest system with 3D-1B and an RGB (red-green-blue) system with 3D-2B-1B are proposed, to produce white LECs.

Photocatalytic Aerobic Dehydrogenation of N-Heterocycles with Ir(III) Photosensitizers Bearing the 2(2'-Pyridyl)benzimidazole Scaffold

Photoredox catalysis constitutes a very powerful tool in organic synthesis, due to its versatility, efficiency, and the mild conditions required by photoinduced transformations. In this paper, we present an efficient and selective photocatalytic procedure for the aerobic oxidative dehydrogenation of partially saturated N-heterocycles to afford the respective N-heteroarenes (indoles, quinolines, acridines, and quinoxalines). The protocol involves the use of new Ir(III) biscyclometalated photocatalysts of the general formula [Ir(C^N)₂(N^N')]Cl, where the C^N ligand is 2-(2,4-difluorophenyl)pyridinate, and N^N' are different ligands based on the 2-(2'-pyridyl)benzimidazole scaffold. In-depth electrochemical and photophysical studies as well as DFT calculations have allowed us to establish structure-activity relationships, which provide insights for the rational design of efficient metal-based dyes in photocatalytic oxidation reactions. In addition, we have formulated a dual mechanism, mediated by the radical anion superoxide, for the above-mentioned transformations.

New Molecularly Engineered Binuclear Ruthenium (II) Complexes for Highly Efficient Near-Infrared Light-Emitting Electrochemical Cell (NIR-LEC)

Abstract: From practical point of view, the stability, response time and efficiency of near-infrared light-emitting electrochemical cell (NIR-LEC) are key factors. By using the high potential of chemical modification potential...

Photodynamic therapy with mitochondria-targeted biscyclometallated Ir(III) complexes. Multi-action mechanism and strong influence of the cyclometallating ligand

Photodynamic therapy is an alternative to classical chemotherapy due to its potential to reduce side effects by a controlled activation of a photosensitizer through local irradiation with light. The photosensitizer then interacts with oxygen and generates reactive oxygen species. Iridium biscyclometallated complexes are very promising photosensitizers due to their exceptional photophysical properties and their ability to target mitochondria. Four Ir(III) biscyclometallated complexes of formula [Ir(C^N)₂(N^N')]Cl, where N^N' is a ligand containing a benzimidazolyl fragment, have been synthesized and characterized. The C^N ligands were 2-phenylpyridinate (ppy) and 2-(2,4-difluorophenyl)pyridinate (dfppy). The complexes exhibited high photostability. The electrochemical and photophysical properties were modulated by both the cyclometallating and the ancillary ligands. The dfppy derivatives yielded the highest emission energy values, quantum yields of phosphorescence and excited state lifetimes. All complexes generated ¹O₂ in aerated solutions upon irradiation. Biological studies revealed that these complexes have a moderate cytotoxicity in the dark against different human cancer cell lines: prostate (PC-3), colon (CACO-2) and melanoma (SK-MEL-28), and against non-malignant fibroblasts (CCD-18Co). However, derivatives with ppy ligands ([1a]Cl, [2a]Cl) yielded a relevant photodynamic activity upon light irradiation (450 nm, 24.1 J cm^-2), with phototoxicity indexes (EC_50,dark/EC_50,light) of 20.8 and 17.3, respectively, achieved in PC-3 cells. Mechanistic studies showed that these complexes are taken up by the cells through endocytosis and preferentially accumulate in mitochondria. Upon photoactivation, the complexes induced mitochondrial membrane depolarization and DNA damage, thus triggering cell death, mainly by apoptosis. Complex [1a]Cl is also able to oxidize NADH. This mitochondria-targeted photodynamic mechanism greatly inhibited the reproductive capacity of cancer cells and provides a valuable alternative to traditional chemotherapy for the controlled treatment of cancer.

Study of a phosphorescent cationic iridium(III) complex displaying a blue-shift in crystals

We report the synthesis and the characterization of a new cationic iridium(III) complex featuring two 1-(p-methoxyphenyl)-5-methoxybenzimidazole cyclometallating ligands and a dimethylbipyridine ancillary ligand. The complex has been fully characterized by 1D and 2D NMR (¹H, ¹³C, ¹⁹F and ³¹P), elemental analysis and high-resolution mass spectrometry (HRMS). The photoluminescence studies performed in a solution, on amorphous powder and on crystals revealed an unexpected behavior. Indeed, the emission spectra observed in both solution (CH₂Cl₂) and amorphous powder samples are centered at around 580 nm, whereas in crystals the emission displays a large hypsochromic shift of ∼800 cm^-1 (λ_em = 558 nm). X-ray diffraction experiments, photophysical studies and DFT calculations allow for rationalizing the hypsochromic shift.

High-Efficiency Deep-Red Light-Emitting Electrochemical Cell Based on a Trinuclear Ruthenium(II)-Silver(I) Complex

Turn-on time is a key factor for lighting devices to be of practical application. To decrease the turn-on time value of a deep-red light-emitting electrochemical cells (DR-LECs), two novel approaches based on molecularly engineered ruthenium phenanthroimidazole complexes were introduced. First, we found that with the incorporation of ionic methylpyridinium group to phenanthroimidazole ligand, the turn-on time of the DR-LECs device was dramatically reduced, from 79 to 27 s. By complexation of ruthenium emitter with Ag⁺, the turn-on time was improved by 85%, and the EQE of DR-device was increased from 0.62 to 0.71%. These results open a new avenue in decreasing the turn-on time without adding ionic electrolytes, leading to an efficient LEC.

Effect of Optical and Morphological Control of Single-Structured LEC Device

We investigated the performance of single-structured light-emitting electrochemical cell (LEC) devices with Ru(bpy)₃(PF₆)₂ polymer composite as an emission layer by controlling thickness and heat treatment. When the thickness was smaller than 120–150 nm, the device performance decreased because of the low optical properties and non-dense surface properties. On the other hand, when the thickness was over than 150 nm, the device had too high surface roughness, resulting in high-efficiency roll-off and poor device stability. With 150 nm thickness, the absorbance increased, and the surface roughness was low and dense, resulting in increased device characteristics and better stability. The heat treatment effect further improved the surface properties, thus improving the device characteristics. In particular, the external quantum efficiency (EQE) reduction rate was shallow at 100 °C, which indicates that the LEC device has stable operating characteristics. The LEC device exhibited a maximum luminance of 3532 cd/m² and an EQE of 1.14% under 150 nm thickness and 100 °C heat treatment.

One-pot photocatalytic transformation of indolines into 3-thiocyanate indoles with new Ir(iii) photosensitizers bearing β-carbolines

Herein, we harness the combination of two photocatalytic reactions, promoted by new Ir(iii) photosensitizers, for the direct access to 3-thiocyanato indoles from indolines in a one-pot process.

Cationic Iridium Complexes with 3,4,5-Triphenyl-4H-1,2,4-Triazole Type Cyclometalating Ligands: Synthesis, Characterizations, and Their Use in Light-Emitting Electrochemical Cells

Cationic iridium complexes that show blue-shifted emission and high phosphorescent efficiency have been pursued for their optoelectronic applications. Five cationic iridium complexes with 3,4,5-triphenyl-4H-1,2,4-triazole (tPhTAZ) type cyclometalating ligands (C^N) and 2,2'-bipyridine or 2-(pyridin-2-yl)-1H-benzo[d]imidazole type ancillary ligands (N^N) have been designed and synthesized. Their structures have been confirmed by X-ray crystallography, and their photophysical and electrochemical properties have been comprehensively characterized. In solution and thin films, the complexes afford efficient yellow to blue-green emission. The highest occupied molecular orbitals (HOMOs) of these complexes are delocalized over the C^N ligand and the iridium ion, and compared with the conventional 2-phenylpyridine (Hppy) ligand, the tPhTAZ ligand largely shifts the emission of the complex toward blue by over 40 nm through stabilizing the HOMO. Moreover, the peripheral phenyl rings in tPhTAZ provide steric hindrance to the complexes, which suppresses phosphorescence concentration-quenching of the complexes, leading to high luminescent efficiencies in neat films. Theoretical calculations have shown that the emission of the complexes originates from either the charge-transfer state (Ir/C^N → N^N) or the C^N/N^N-centered ³π-π* state, depending on the local surrounding of the complex. The complexes exhibit good electrochemical stability with reversible oxidation and reduction processes in solution. Solid-state light emitting electrochemical cells (LECs) using the complexes afford yellow to blue-green emission, with peak current efficiencies of up to 34.7 cd A^-1 and maximum brightness of up to 256 cd m^-2 at 3.0 V, which are among the highest for LECs based on cationic iridium complexes reported so far, indicating the great potential for the use of tPhTAZ-type C^N ligands in construction of cationic iridium complexes for LEC applications.

Synthesis, Photophysics, and Reverse Saturable Absorption of trans-Bis-cyclometalated Iridium(III) Complexes (C^N^C)Ir(R-tpy)+ (tpy = 2,2':6',2″-Terpyridine) with Broadband Excited-State Absorption

Extending the bandwidth of triplet excited-state absorption in transition-metal complexes is appealing for developing broadband reverse saturable absorbers. Targeting this goal, five bis-terdentate iridium(III) complexes (Ir1-Ir5) bearing trans-bis-cyclometalating (C^N^C) and 4'-R-2,2':6',2″-terpyridine (4'-R-tpy) ligands were synthesized. The effects of the structural variation in cyclometalating ligands and substituents at the tpy ligand on the photophysics of these complexes have been systematically explored using spectroscopic methods (i.e., UV-vis absorption, emission, and transient absorption spectroscopy) and time-dependent density functional theory (TDDFT) calculations. All complexes exhibited intensely structured ¹π,π* absorption bands at <400 nm and broad charge transfer (¹CT)/¹π,π* transitions at 400-600 nm. Ligand structural variations exerted a very small effect on the energies of the ¹CT/¹π,π* transitions; however, they had a significant effect on the molar extinction coefficients of these absorption bands. All complexes emitted featureless deep red phosphorescence in solutions at room temperature and gave broad-band and strong triplet excited-state absorption ranging from the visible to the near-infrared (NIR) spectral regions, with both originating from the ³π,π*/³CT states. Although alteration of the ligand structures influenced the emission energies slightly, these changes significantly affected the emission lifetimes and quantum yields, transient absorption spectral features, and the triplet excited-state quantum yields of the complexes. Except for Ir3, the other four complexes all manifested reverse saturable absorption (RSA) upon nanosecond laser pulse excitation at 532 nm, with the decreasing trend of RSA following Ir2 ≈ Ir4 > Ir1 > Ir5 > Ir3. The RSA trend corresponded well with the strength of the excited-state and ground-state absorption differences (ΔOD) at 532 nm for these complexes.

Rational Design of Efficient Organometallic Ir(III) Complexes for High-Performance, Flexible, Monochromatic, and White Light-Emitting Electrochemical Cells

Highly efficient light-emitting electrochemical cells (LECs) have attracted tremendous interest because of their simple structures and low-cost fabrication processing, showing great potential for full-color displays and solid-state lighting. In this work, we rationally designed and synthesized two red-emitting cationic Ir(III) complexes, [Ir(tBuPBI)₂(biq)]PF₆ (R1) and [Ir(tBuPBI)₂(qibi)]PF₆ (R2), in which a tert-butyl-functionalized 1,2-diphenyl-1H-benzo[d]imidazole (PBI) unit and conjugated 2,2'-biquinoline (biq) and 2-(1-phenyl-1H-benzo[d]imidazol-2-yl)quinolone (qibi) were employed as cyclometalated and ancillary ligands, respectively. The introduced tert-butyl group led to homogeneous and highly emissive thin films by increasing the solubility and suppressing the strong intermolecular interactions due to steric hindrance. Based on the abovementioned high-quality emissive layer, high-efficiency LECs were achieved. An efficient red-emitting LEC fabricated on a glass substrate achieved a current efficiency (η_C) of 7.18 cd/A and an external quantum efficiency (η_ext) of 9.32%. By doping both complexes into a blue-green-emitting cationic Ir(III) complex, high-performance white LECs were also successfully fabricated with Commission International de L'Eclairage (CIE) coordinates of (0.39,0.39), a η_C of 17.43 cd/A, and a η_ext of 8.92%. In addition, we also fabricated flexible red and white LECs with outstanding efficiencies and mechanical flexibilities. The η_C and η_ext values of a flexible white LEC could be as high as 13.50 cd/A and 6.86%, respectively. The efficiency of the flexible device remained at approximately 95% of the initial value after 500 bends with a radius of curvature of 5 mm, demonstrating the great potential of these complexes for full-color displays and flexible optoelectronics.

Synthesis of α-amino nitriles through one-pot selective Ru-photocatalyzed oxidative cyanation of amines

A new family of Ru(ii) photocatalysts exhibits excellent performance in the efficient and eco-friendly one-pot preparation of α-amino nitriles from primary and secondary amines.

Azole-containing cationic bis-cyclometallated iridium(iii) isocyanide complexes: a theoretical insight into the emission energy and emission efficiency

Using a density functional theory approach, we explore the emission properties of a family of bis-cyclometallated cationic iridium(iii) complexes of general formula [Ir(C^N)2(CN-tert-Bu)2]+ that have tert-butyl isocyanides as neutral auxiliary ligands. Taking the [Ir(ppy)2(CN-tert-Bu)2]+ complex (Hppy = 2-phenylpyridine) as a reference, the effect of replacing the pyridine ring in the cyclometallating ppy ligand by a five-membered azole ring has been examined. To this end, two series of complexes differing by the nature of the atom (either nitrogen or carbon) linking the azole to the phenyl ring of the cyclometallating ligand have been designed. Each series is composed of three molecules having an increasing number of nitrogen atoms (2 to 4) in the azole ring. The emission energies computed for the azole-containing [Ir(C^N)2(CN-tert-Bu)2]+ complexes show a generalized blue-shift compared to [Ir(ppy)2(CN-tert-Bu)2]+, in agreement with the experimental data available for two of the six complexes designed here. The electronic nature of the lowest-lying triplet (T1) is clearly established as a ligand-centred (3LC) state associated with the cyclometallating ligands, and cannot be described as a simple HOMO → LUMO promotion. Therefore, no clear trend based on the sole use of molecular orbital energies can be inferred to predict the emission properties. The significant oscillation in the emission quantum yield (ranging from 0.1% to 52%) experimentally reported is rationalized by the energy gap between the emitting T1 state and a non-radiative triplet state having metal-centred (3MC) d-d* nature. On the basis of such a model, two of the here proposed systems are expected to display significant emission quantum yields in the blue region of the visible spectra, which make them good candidates for electroluminescent applications.

A novel coordination mode of κ1-N-Br-pyridylbenz-(imida, oxa or othia)-zole to Pt(ii): synthesis, characterization, electrochemical and structural analysis

Three novel platinum(ii) complexes with the general formula [trans-Pt(Br-PyBenz-X)(Cl)₂(DMSO)] containing Br-pyridylbenz(imida, oxa or othia)zole derivatives, under an unusual N-κ¹-coordination mode were synthesized.

Retracted Article: Facile preparation of bithiazole-based material for inkjet printed light-emitting electrochemical cell

Light-emitting electrochemical cell of bithiazole-based material was fabricated by solution processing rendered high external quantum efficiency over 12.8% and luminance of 1.8 10⁴ cd m⁻².

Light-emitting electrochemical cell of bithiazole-based material was fabricated by solution processing rendered high external quantum efficiency over 12.8% and luminance of 1.8 10⁴ cd m^−2.

Strong Influence of the Ancillary Ligand over the Photodynamic Anticancer Properties of Neutral Biscyclometalated IrIII Complexes Bearing 2-Benzoazole-Phenolates

In this paper, the synthesis, comprehensive characterization and biological and photocatalytic properties of two series of neutral Ir^III biscyclometalated complexes of general formula [Ir(C^N)₂ (N^O)], where the N^O ligands are 2-(benzimidazolyl)phenolate-N,O (L1, series a) and 2-(benzothiazolyl)phenolate-N,O (L2, series b), and the C^N ligands are 2-(phenyl)pyridinate or its derivatives, are described,. Complexes of types a and b exhibit dissimilar photophysical and biological properties. In vitro cytotoxicity tests conclusively prove that derivatives of series a are harmless in the dark against SW480 cancer cells (colon adenocarcinoma), but express enhanced cytotoxicity versus the same cells after stimulation with UV or blue light. In contrast, complexes of type b show a very high cytotoxic activity in the dark, but low photosensitizing ability. Thus, the ancillary N^O ligand is the main factor in terms of cytotoxic activity both in the dark and upon irradiation. However, the C^N ligands play a key role regarding cellular uptake. In particular, the complex of formula [Ir(dfppy)₂ (L1)] (dfppy=2-(4,6-difluorophenyl)pyridinate) [3 a] has been identified as both an efficient photosensitizer for ¹ O₂ generation and a potential agent for photodynamic therapy. These capabilities are probably related to a combination of its notable cellular internalization, remarkable photostability, high photoluminescence quantum yield, and long triplet excited-state lifetime. Both types of complexes exhibit notable catalytic activity in the photooxidation of thioanisole and S-containing aminoacids with full selectivity.

Challenging Conventional Wisdom: Finding High-Performance Electrodes for Light-Emitting Electrochemical Cells

The light-emitting electrochemical cell (LEC) exhibits capacity for efficient charge injection from two air-stable electrodes into a single-layer active material, which is commonly interpreted as implying that the LEC operation is independent of the electrode selection. Here, we demonstrate that this is far from the truth and that the electrode selection instead has a strong influence on the LEC performance. We systematically investigate 13 different materials for the positive anode and negative cathode in a common LEC configuration with the conjugated polymer Super Yellow as the electroactive emitter and find that Ca, Mn, Ag, Al, Cu, indium tin oxide (ITO), and Au function as the LEC cathode, whereas ITO and Ni can operate as the LEC anode. Importantly, we demonstrate that the electrochemical stability of the electrode is paramount and that particularly electrochemical oxidation of the anode can prohibit the functional LEC operation. We finally report that it appears preferable to design the device so that the heights of the injection barriers at the two electrode/active material interfaces are balanced in order to mitigate electrode-induced quenching of the light emission. As such, this study has expanded the set of air-stable electrode materials available for functional LEC operation and also established a procedure for the evaluation and design of future efficient electrode materials.

Recent Progress in Sublimable Cationic Iridium(III) Complexes for Organic Light-Emitting Diodes

Sublimable cationic iridium(III) complexes consisting of light-emitting coordinated iridium(III) cations and nonluminous negative counter-ions, show excellent photophysical properties, superior electrochemical behaviors and high thermal stabilities, therefore have emerged as a new library of phosphorescent materials for various organic optoelectronic devices. Here we summarize and highlight the recent progress in sublimable cationic iridium(III) complexes, regarding the material design strategies, synthetic routes, photoluminescent characteristics in both solutions and neat films, together with the current utilization in organic light-emitting diodes based on the emissive material layers fabricated by vacuum evaporation deposition. Finally, we present a brief outlook thereon, indicating the great promise and brilliant application prospect of sublimable cationic iridium(III) complexes in future flat-panel display and solid-state lighting technology.

Controlling Ion Distribution for High-Performance Organic Light-Emitting Diodes Based on Sublimable Cationic Iridium(III) Complexes

Sublimable charged iridium(III) complexes are becoming an attractive family of new phosphors and making their way into vacuum-evaporated-deposited organic light-emitting diodes, while it remains challenging to achieve high device performance. Here, we demonstrate a substantial mitigation of exciton quenching not only by reducing the dopant concentration, but also by controlling the ion distribution in the emissive material layers. We, therefore, achieved green luminescence with high brightness, superior efficiencies, and low driving voltages. Following this strategy, we further developed another six sublimable charged iridium(III) complexes and attained blue-green, yellow, and red-emitting devices with record-high performance. This study represents an important advance in the construction of bright electroluminescence from ionic transition metal complexes and shows their great promise in various optoelectronic applications.

Visible-Light-Driven Hydrogen Production and Polymerization using Triarylboron-Functionalized Iridium(III) Complexes

The development of novel iridium(III) complexes has continued as an important area of research owing to their highly tunable photophysical properties and versatile applications. In this report, three heteroleptic dimesitylboron-containing iridium(III) complexes, [Ir(p-B-ppy)₂ (N^N)]⁺ {p-B-ppy=2-(4-dimesitylborylphenyl)pyridine; N^N=dipyrido[3,2-a:2',3'-c]phenazine (dppz) (1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (2), and 1,10-phenanthroline (phen) (3)}, were prepared and fully characterized electrochemically, photophysically, and computationally. Altering the conjugated length of the N^N ligands allowed us to tailor the photophysical properties of these complexes, especially their luminescence wavelength, which could be adjusted from λ=583 to 631 nm in CH₂ Cl₂ . All three complexes were evaluated as visible-light-absorbing sensitizers for the photogeneration of hydrogen from water and as photocatalysts for the photopolymerization of methyl methacrylate. The results showed that all of them were active in both photochemical reactions. High activity for the photosensitizer (over 1158 turnover numbers with 1) was observed, and the system generated hydrogen even after 20 h. Additionally, poly(methyl methacrylate) with a relatively narrow molecular-weight distribution was obtained if an initiator (i.e., ethyl α-bromophenylacetate) was used. The living character of the photoinduced polymerization was confirmed on the basis of successful chain-extension experiments.

Synthesis and characterization of mixed-ligand silver(I) saccharinate complex containing (2-(2-pyridyl)benzimidazole

Se sintetizó un nuevo compuesto de coordinación de plata, [Ag(sac)(pbi)], por reacción de sacarinato de plata(I) con 2-(2-piridil)bencimidazol (pbi) con un rendimiento de 64%. La caracterización se realizó por análisis elemental, espectroscopia IR, UV-Visible, XPS, 1H-RMN y 13C-RMN. De acuerdo con los resultados obtenidos la plata está coordinada a través de tres átomos de nitrógeno, uno del sacarinato y los dos restantes del 2-(2-piridil)-bencimidazol formando con este ligando un anillo quelato de cinco miembros.

Enhancing the Overall Performances of Blue Light-Emitting Electrochemical Cells by Using an Electron-Injecting/Transporting Ionic Additive

Light-emitting electrochemical cells (LECs) have emerged as a promising emissive thin-film technology for next-generation solid-state lighting. However, blue LECs show low performances, which has remained a bottleneck for the fabrication of white LECs for lighting applications. Here, we demonstrate a remarkable enhancement of overall device performance for blue LECs by using an electron-injecting/transporting ionic additive, that is, [Zn(bpy)₃](PF₆)₂ (bpy is 2.2'-bipyridine, PF₆^- is hexafluorophosphate). It is revealed that adding [Zn(bpy)₃](PF₆)₂ into the active layers of blue LECs accelerates the device response, simultaneously enhances the brightness and efficiency, reduces the efficiency roll-offs, significantly improves the blue color stability upon the continuous electrical operation, and enhances the device operational stability at optimized conditions. The remarkable enhancement of the overall device performance upon adding [Zn(bpy)₃](PF₆)₂ results from facilitated electron injection/transport and thus more balanced electron-hole recombination and more centered recombination zone, as well as the reduction of phosphorescence concentration quenching in the LECs. The work demonstrates for the first time that the use of electron-injecting/transporting ionic additives such as [Zn(bpy)₃](PF₆)₂ is a facile yet effective strategy to remarkably boost the overall performances of blue LECs.