Enantioselective sensing by collective circular dichroism.

Quantitative determination and in situ monitoring of molecular chirality at extremely low concentrations is still challenging with simple optics because of the molecular-scale mismatch with the incident light wavelength. Advances in spectroscopy1-4 and nanophotonics have successfully lowered the detection limit in enantioselective sensing, as it can bring the microscopic chiral characteristics of molecules into the macroscopic scale5-7 or squeeze the chiral light into the subwavelength scale8-17. Conventional nanophotonic approaches depend mainly on the optical helicity density8,9 by localized resonances within an individual structure, such as localized surface plasmon resonances (LSPRs)10-16 or dielectric Mie resonances17. These approaches use the local chiral hotspots in the immediate vicinity of the structure, whereas the handedness of these hotspots varies spatially. As such, these localized resonance modes tend to be error-prone to the stochasticity of the target molecular orientations, vibrations and local concentrations18,19. Here we identified enantioselective characteristics of collective resonances (CRs)20 arising from assembled 2D crystals of isotropic, 432-symmetric chiral gold nanoparticles (helicoids)21,22. The CRs exhibit a strong and uniform chiral near field over a large volume above the 2D crystal plane, resulting from the collectively spinning, optically induced dipoles at each helicoid. Thus, energy redistribution by molecular back action on the chiral near field shifts the CRs in opposite directions, depending on the handedness of the analyte, maximizing the modulation of the collective circular dichroism (CD).

Synthesis of Thermally Stable and Highly Luminescent Cs5 Cu3 Cl6 I2 Nanocrystals with Nonlinear Optical Response.

Low-dimensional Cu(I)-based metal halide materials are gaining attention due to their low toxicity, high stability and unique luminescence mechanism, which is mediated by self-trapped excitons (STEs). Among them, Cs5 Cu3 Cl6 I2 , which emits blue light, is a promising candidate for applications as a next-generation blue-emitting material. In this article, an optimized colloidal process to synthesize uniform Cs5 Cu3 Cl6 I2 nanocrystals (NCs) with a superior quantum yield (QY) is proposed. In addition, precise control of the synthesis parameters, enabling anisotropic growth and emission wavelength shifting is demonstrated. The synthesized Cs5 Cu3 Cl6 I2 NCs have an excellent photoluminescence (PL) retention rate, even at high temperature, and exhibit high stability over multiple heating-cooling cycles under ambient conditions. Moreover, under 850-nm femtosecond laser irradiation, the NCs exhibit three-photon absorption (3PA)-induced PL, highlighting the possibility of utilizing their nonlinear optical properties. Such thermally stable and highly luminescent Cs5 Cu3 Cl6 I2 NCs with nonlinear optical properties overcome the limitations of conventional blue-emitting nanomaterials. These findings provide insights into the mechanism of the colloidal synthesis of Cs5 Cu3 Cl6 I2 NCs and a foundation for further research.

Triptycene-Fused Sterically Shielded Multi-Resonance TADF Emitter Enables High-Efficiency Deep Blue OLEDs with Reduced Dexter Energy Transfer.

Designing multi-resonance (MR) emitters that can simultaneously achieve narrowband emission and suppressed intermolecular interactions is challenging for realizing high color purity and stable blue organic light-emitting diodes (OLEDs). Herein, a sterically shielded yet extremely rigid emitter based on a triptycene-fused B,N core (Tp-DABNA) is proposed to address the issue. Tp-DABNA exhibits intense deep blue emissions with a narrow full width at half maximum (FWHM) and a high horizontal transition dipole ratio, superior to the well-known bulky emitter, t-DABNA. The rigid MR skeleton of Tp-DABNA suppresses structural relaxation in the excited state, with reduced contributions from the medium- and high-frequency vibrational modes to spectral broadening. The hyperfluorescence (HF) film composed of a sensitizer and Tp-DABNA shows reduced Dexter energy transfer compared to those of t-DABNA and DABNA-1. Notably, deep blue TADF-OLEDs with the Tp-DABNA emitter display higher external quantum efficiencies (EQEmax =24.8 %) and narrower FWHMs (≤26 nm) than t-DABNA-based OLEDs (EQEmax =19.8 %). The HF-OLEDs based on the Tp-DABNA emitter further demonstrate improved performance with an EQEmax of 28.7 % and mitigated efficiency roll-offs.

Doubly Boron-Doped TADF Emitters Decorated with ortho-Donor Groups for Highly Efficient Green to Red OLEDs.

Doubly boron-doped thermally activated delayed fluorescence (TADF) emitters based on a 9,10-diboraanthracene (DBA) acceptor decorated with ortho-donor groups (Cz2oDBA, 2; BuCz2oDBA, 3; DMAC2oDBA, 4) are prepared to realize high-efficiency green-to-red organic light-emitting diodes (OLEDs). X-ray diffraction analyses of 2 and 4 reveal the symmetrical and highly twisted ortho-donor-acceptor-donor (D-A-D) structure of the emitters. The twisted conformation leads to a very small energy splitting (ΔEST <0.08 eV) between the excited singlet and triplet states that gives rise to strong TADF, as supported by theoretical studies. Depending on the strength of the donor moieties, the emission color is fine-tuned in the visible region from green (2) to yellow (3) to red (4). Carbazole-containing 2 and 3 exhibit high photoluminescence quantum yields (PLQYs) approaching 100 %, whereas DMAC-substituted 4 is moderately emissive (PLQY=44 %) in a doped host film. Highly efficient green-to-red TADF-OLEDs are realized with the proposed ortho-D-A-D compounds as emitters. The green and yellow OLEDs incorporating Cz2oDBA (2) and BuCz2oDBA (3) emitters exhibit high external quantum efficiencies (EQEs) of 26.6 % and 21.6 %, respectively. In particular, the green device shows an excellent power efficiency above 100 lm W-1 . A red OLED fabricated with a DMAC2oDBA (4) emitter exhibits a maximum EQE of 10.1 % with an electroluminescence peak at 615 nm.

Donor-Acceptor-Appended Triarylboron Lewis Acids: Ratiometric or Time-Resolved Turn-On Fluorescence Response toward Fluoride Binding.

Triarylboron Lewis acid compounds (CzmBoT (1c) and DPAmBoT (2c)), in which carbazole (Cz) or diphenylamine (DPA) donors are linked with a triazine acceptor in the ortho position of the phenylene ring are prepared and characterized. The treatment of 1c and 2c with the fluoride anion produces the corresponding fluoride adducts [1cF]- and [2cF]- as a tetraethylammonium salt. An X-ray diffraction study of [1cF]- reveals a twisted conformation between the Cz and phenylene rings. The Cz-containing 1c shows a ratiometric fluorescence change upon fluoride binding, while the DPA-containing 2c exhibits a turn-on fluorescence response in tetrahydrofuran. In particular, both fluoride adducts exhibit thermally activated delayed fluorescence (TADF) properties with microsecond-range lifetimes. Electrochemical and theoretical analysis suggests that the intramolecular charge-transfer transition from the donor to a conjugated acceptor fragment is switched to the donor to a triazine transition after fluoride binding. Theoretical analysis further demonstrates the twisted structure, effective highest occupied molecular orbital-lowest unoccupied molecular orbital separation, and the small energy splitting between the excited singlet and triplet states for the fluoride adducts, with all supporting the observed TADF. The time-resolved fluorescence measurements of 2c in the presence of both fluoride and a competitive fluorescent dye (Coumarin 6) effectively eliminate the short-lived fluorescence of a dye, retaining long-lived fluorescence signals originating only from [2cF]-.

Naphthalene Benzimidazole Based Neutral Ir(III) Emitters for Deep Red Organic Light-Emitting Diodes.

Rigid naphthalene benzimidazole (NBI) based ligands (L1 and L2) are synthesized and utilized to make deep red phosphorescent cyclometalated iridium(III) complexes ([Ir(NBI)2(PyPzCF3)] (1) and [Ir(DPANBI)2(PyPzCF3)] (2)). Complexes 1 and 2 are prepared from the reaction of L1/L2 with the aid of ancillary ligands (PyPzCF3, 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridine) in a two step method. The complexes are characterized by analytical and spectroscopic methods, as well as X-ray diffraction for 1. These complexes show a strong emission in the range of 635-700 nm that extends up to the near-infrared region (800 nm). The introduction of the diphenylamino (DPA) donor group on the naphthalene unit leads to a further red-shift in the emission. The complexes exhibit radiative quantum efficiency (ΦPL) of 0.27-0.29 in poly(methylmethacrylate) film and relatively short phosphorescence decay lifetimes (τ = 1.1-3.5 µs). The structural, electronic, and optical properties are investigated with the support of density functional theory (DFT) and time-dependent-DFT calculations. The calculation results indicate that the lowest-lying triplet (T1) excited state of 1 has a mixed metal-to-ligand charge transfer (3MLCT) and ligand-centered (3LC) character, while 2 shows a dominant 3LC character. Deep red-emitting organic light-emitting diodes fabricated using 1 as a dopant display a maximum external quantum efficiency of 10.9% with the CIE color coordinates of (0.690, 0.294), with an emission centered at 644 and 700 nm. Similarly, the emitter 2 also shows a maximum external quantum efficiency of 6.9% with emissions at 657 and 722 nm.

Severe late dysphagia after multimodal treatment of stage III/IV laryngeal and hypopharyngeal cancer.

BACKGROUND: Long-term side effects after radiotherapy for organ preservation 'could deteriorate' the laryngeal function. This study intended to identify the incidence of severe late dysphagia following the multimodal treatment for stage III/IV laryngeal and hypopharyngeal cancer 'to evaluate the function of larynx'. METHODS: The medical records of patients successfully treated for laryngeal and hypopharyngeal cancer with a multimodal approach, including radiotherapy, were retrospectively analyzed. 'Functional larynx was defined as tolerable oral diet without severe late dysphagia or tracheostoma'. RESULTS: The study included 99 patients with a median follow-up period of 72 months. 'Tracheostomy during the follow-up period was required in only one patient due to aspiration pneumonia, and dysphagia is the main determinant for functional larynx'. The probability of maintaining functional larynx was 63% for 10 years, when the treatment was started with radiotherapy or concurrent chemoradiotherapy. In upfront surgery (operation first and adjuvant radiotherapy/concurrent chemoradiotherapy) group, 37% of patients required total laryngectomy as primary treatment and 43% of patients could maintain laryngeal function for 10 years. And severe late dysphagia in the latter group developed mainly after laryngeal preservation surgery. The patients aged ≥65 years showed significantly higher incidence of dysphagia. Severe late dysphagia was very rare in laryngeal cancer successfully cured with radiotherapy/concurrent chemoradiotherapy (1/25, 4%); however, it gradually increased over time in hypopharyngeal cancer patients showing a statistically significant difference from laryngeal cancer patients (P = 0.040). CONCLUSION: Severe late dysphagia occurred in 19.2% of patients treated for laryngeal and hypopharyngeal cancers, regardless of whether treatment started with radiotherapy/concurrent chemoradiotherapy or surgery.

Neurite Guidance on Laser-Scribed Reduced Graphene Oxide.

This paper describes a one-step, chemical-free method to generate micropatterned in vitro neuronal networks on chemically unmodified reduced graphene oxide. The suggested method relies on infrared-based photothermal reduction of graphene oxide, which concurrently leads to the formation of submicrometer-scale surface roughness that promotes neuronal adhesion and guides neurite outgrowth. A commercially available laser source (LightScribe DVD drive) controlled by a computer software can be used to reduce graphene oxide (GO), and its repetitive scribing to a GO film brings about gradual increase and decrease in electrical conductivity and neurite guiding ability of the scribed regions, respectively. Our results also indicate that the observed adhesion-promoting and neurite guiding effect originate from the contrast in surface nanotopography, but not that in conductivity. This method is readily applicable to diverse graphene-based biomedical devices.

Supramolecular Pt(II) and Ru(II) Trigonal Prismatic Cages Constructed with a Tris(pyridyl)borane Donor.

We report a novel example of supramolecular cages containing a Lewis acidic trigonal boron center. Self-assembly of the tris(pyridyl)borane donor 1 with diruthenium (2) or platinum (3), as an electron acceptor, furnished boron-containing trigonal prismatic supramolecular cages 5 and 6, which were characterized by 1H NMR and electrospray ionization time-of-flight mass spectroscopy and X-ray crystallography. The molecular structure of cage 5 was confirmed as a trigonal prismatic cage with an inner dimension of about 400 Å3. The fluoride binding properties of borane ligand 1 and Pt cage 6 were studied. UV/vis absorption titration studies demonstrated that the boron center of cage 6 undergoes strong binding interaction with the fluoride ion, with an estimated binding constant of 1.3 × 1010 M-2 in acetone based on the 1:2 binding isotherm. The binding was also confirmed by 1H NMR titration. Photoluminescence titration studies showed that cage 6 emitted borane-centered fluorescence (τ = 2.21 ns), which was gradually quenched upon addition of fluoride. When excess fluoride was added to a solution of 6, however, dissociation of the pyridyl ligand from the Pt(II) center was observed.

Nido-Carboranes: Donors for Thermally Activated Delayed Fluorescence.

An approach to the design of nido-carborane-based luminescent compounds that can exhibit thermally activated delayed fluorescence (TADF) is proposed. 7,8-Dicarba-nido-undecaboranes (nido-carboranes) having various 8-R groups (R=H, Me, i-Pr, Ph) are appended to the meta or para position of the phenyl ring of the dimesitylphenylborane (PhBMes2 ) acceptor, forming donor-acceptor compounds (nido-m1-m4 and nido-p1-p4). The bulky 8-R group and meta substitution of the nido-carborane are essential to attain a highly twisted arrangement between the donor and acceptor moieties, leading to a very small energy splitting between the singlet and triplet excited states (ΔEST <0.05 eV for nido-m2, -m3, and -p3). These compounds exhibit efficient TADF with microsecond-range lifetimes. In particular, nido-m2 and -m3 display aggregation-induced emission (AIE) with TADF properties.

Induced dipole in vanadium-doped zinc oxide nanosheets and its effects on photoelectrochemical water splitting.

Appropriate control of energy band bending at the interface between semiconductors and electrolytes are closely related to performance of photoelectrochemical (PEC) water splitting. Dipoles formed near the surface of semiconductors induces energy band bending at the interface. Energy band bending control has been demonstrated by employing charged molecules and piezoelectric materials. However, chemical and piezoelectric approaches have demerit of chemical instability and inducement of instantaneous dipole, respectively. To overcome these problems, we adopted the ferroelectric material for PEC water splitting, where spontaneous dipoles in the material can be oriented by applying external electric field. In this work, we hydrothermally synthesized vanadium (V)-doped ferroelectric ZnO nanosheets and employed to systematically investigate the dipole effect on performance of V-doped ZnO PEC for water oxidation. Consequently, positively polarized V-doped ZnO photoanode exhibits 125% enhanced water splitting efficiency compared to negatively polarized ones due to favorable band bending for carrier transport from semiconductor to water.

Morphology-Directed Selective Production of Ethylene or Ethane from CO2 on a Cu Mesopore Electrode.

The electrocatalytic conversion of CO2 to value-added hydrocarbons is receiving significant attention as a promising way to close the broken carbon-cycle. While most metal catalysts produce C1 species, such as carbon monoxide and formate, the production of various hydrocarbons and alcohols comprising more than two carbons has been achieved using copper (Cu)-based catalysts only. Methods for producing specific C2 reduction outcomes with high selectivity, however, are not available thus far. Herein, the morphological effect of a Cu mesopore electrode on the selective production of C2 products, ethylene or ethane, is presented. Cu mesopore electrodes with precisely controlled pore widths and depths were prepared by using a thermal deposition process on anodized aluminum oxide. With this simple synthesis method, we demonstrated that C2 chemical selectivity can be tuned by systematically altering the morphology. Supported by computational simulations, we proved that nanomorphology can change the local pH and, additionally, retention time of key intermediates by confining the chemicals inside the pores.

Homoleptic Tris-Cyclometalated Iridium Complexes with Substituted o-Carboranes: Green Phosphorescent Emitters for Highly Efficient Solution-Processed Organic Light-Emitting Diodes.

Homoleptic tris-cyclometalated iridium complexes, fac-Ir[5-(2-RCB)ppy]3 (3a-3c; CB = o-carboran-1-yl; ppy = 2-phenylpyridinato-C(2),N; R = H (3a), Me (3b), (i)Bu (3c)) with 2-R-substituted o-carboranes at the 5-position of the ppy ligand, were prepared and characterized. X-ray diffraction analysis of 3a and 3c revealed that the three C^N ligands adopt a fac-arrangement around the Ir atom and that the carboranyl C-C bond distance increases with increasing steric effects of the 2-R substituent. The phosphorescence wavelengths of the complexes were apparently blue-shifted by ca. 20 nm (λem = 487-493 nm) compared to that of the parent fac-Ir(ppy)3 (4; λem = 508 nm). In particular, 3a-3c were highly emissive in toluene, and the phosphorescence quantum efficiencies of 3a and 3b (ΦPL = 0.95-0.98) were comparable to that of 4. Solution-processed electroluminescent devices incorporating 3a-3c as emitters displayed green light with high performance, and devices based on the 3c dopant showed the highest performance. In particular, the devices based on 3c exhibited performance more than double of that of the device based on 4 in terms of current efficiency (29.6 cd/A for 3c vs 15.8 cd/A for 4 at 4 wt % Ir and 1000 cd/m(2)), power efficiency (11.0 lm/W for 3c vs 6.3 lm/W for 4), and external quantum efficiency (10.2% for 3c vs 4.7% for 4) over a wide range of luminance. The higher PL quantum yields of doped host films with 3c than those with 4 at high dopant concentrations above 8 wt % suggested that along with high phosphorescence quantum efficiency, the steric bulkiness of the 2-(i)Bu-substituted o-carborane in 3c plays a crucial role in improving device performance.

Iridium Cyclometalates with Tethered o-Carboranes: Impact of Restricted Rotation of o-Carborane on Phosphorescence Efficiency.

Iridium(III) cyclometalates (1c and 2c) in which the two carborane units on the 4- or 5-positions of 2-phenylpyridine (ppy) ligands were tethered by an alkylene linker were prepared to investigate the effect of free rotation of o-carborane on phosphorescence efficiency. In comparison with the unlinked complex, tethering the o-carboranes to the 5-positions of ppy ligands (2c) enhanced phosphorescence efficiency by over 30-fold in polar medium (Φ(PL) = 0.37 vs 0.011 in THF), while restricting the rotation of o-carborane at the 4-positions (1c) negatively affected the phosphorescence efficiency. The different effects of restricted rotation of o-carborane on phosphorescence efficiency were likely a result of the different variations of the carboranyl C-C bond distances in the excited state.

Selective Formation of Heterometallic Ru-Ag Supramolecules via Stoichiometric Control of Multiple Different Tectons.

Stoichiometric control of Ru, Ag, and tetrazolyl ligands resulted in the formation of different heterometallic Ru-Ag supramolecular architectures. Although the reaction of Ru and 5-(2-hydroxyphenyl)-1H-tetrazolyl (LH2) in a molar ratio of 2:1 or 6:4 resulted in the formation of dimeric or hexameric Ru complexes, Ag metal ions caused the Ru complexes to form three-dimensional cylindrical Ru6Ag6L6 and double-cone-shaped Ru6Ag8L6 complexes by occupying vacant coordination sites.

Manipulation of phosphorescence efficiency of cyclometalated iridium complexes by substituted o-carboranes.

A series of [(C^N)2 Ir(acac)] complexes [{5-(2-R-CB)ppy}2 Ir(acac)] (3 a-3 g; acac=acetylacetonate, CB=o-carboran-1-yl, ppy=2-phenylpyridine; R=H (3 a), Me (3 b), iPr (3 c), iBu (3 d), Ph (3 e), CF3 C6 H4 (3 f), C6 F5 (3 g)) with various 2-R-substituted o-carboranes at the 5-position in the phenyl ring of the ppy ligand were prepared. X-ray diffraction studies revealed that the carboranyl CC bond length increases with increasing steric and electron-withdrawing effects from the 2-R substituents. Although the absorption and emission wavelengths of the complexes are almost invariant to the change of 2-R group, the phosphorescence quantum efficiency varies from highly emissive (ΦPL ≈0.80 for R=H, alkyl) to poorly emissive (R=aryl) depending on the 2-R group and the polarity of the medium. Theoretical studies suggest that 1) the almost nonemissive nature of the 2-aryl-substituted complexes is mainly attributable to the large contribution to the LUMO in the S1 excited state from an o-carborane unit and 2) the variation in the CC bond length between the S0 and T1 state structures increases with increasing steric (2-alkyl) and electronic effects (2-aryl) of the 2-R substituent and the polarity of the solvent. The solution-processed electroluminescence (EL) devices that incorporated 3 b and 3 d as emitters displayed higher performance than the device based on the parent [(ppy)2 Ir(acac)] complex. Along with the high phosphorescence efficiency, the bulkiness of the 2-R-o-carborane unit is shown to play an important role in improving device performance.

Transition-Metal-Free Synthesis of 2-Substituted Methyl Benzo[b]furan-3-carboxylates.

A concise and highly efficient synthetic pathway was developed for 2-substituted methyl benzo[b]furan-3-carboxylates. This method provides convenient and cost-effective access for 2-substituted methyl benzo[b]furan-3-carboxylates without the use of a transition metal catalyst for synthesis. Furthermore, in most cases, this method gives excellent yields and conventional flash column chromatography is not needed for purification.

Biomedical and biochemical applications of self-assembled metallacycles and metallacages.

Metal ions and metal complexes with organic molecules are ubiquitous in nature. Bulk metal ions of Na, K, Mg, and Ca constitute as much as 1% of human body weight. The remaining trace ions, most commonly of Fe, Ni, Cu, Mn, Zn, Co, Mo, and V, make up ∼0.01% by weight, but their importance in biological processes cannot be overstated. Although nature is limited to the use of bioavailable metal ions, many rarer transition metals can elicit novel biological responses when they interact with biomolecules. For this reason, metal-biomolecule complexes are of interest in medicinal applications. A well-known example is cisplatin, which contains Pt, rare in nature, but highly effective in this context as an anticancer drug in the form of cis-Pt(NH3)2Cl2 and analogous Pt(II) complexes. This and other examples have led to strong interest in discovering new metalloanticancer drugs. In this Account, we describe recent developments in this area, particularly, using coordination-driven self-assembly to form tunable supramolecular coordination complexes (SCCs) with biomedical applications. Coordination-driven self-assembly describes the spontaneous formation of metal-ligand bonds in solution, transforming molecular building blocks into single, 2D metallacycles, or 3D metallacages depending on the directionality of the precursors used. Such SCCs have well-defined internal cavities and simple pre- or post-self-assembly functionalizations. They are highly tunable both spatially and electronically. Metal ions are necessary structural elements for the directional bonding approach, which can be exploited to provide biological activity to an SCC, particularly for Pt- and Ru-based structures. Since these two metals are not only among the most commonly used for coordination-driven self-assembly but are also the basis for a number of small molecule anticancer agents, researchers have evaluated a growing number of SCCs for their antitumor properties. The biological application of SCCs is still an emergent field of study, but the examples discussed in this Account confirm that supramolecular scaffolds have relevance to a wide variety of biochemical and biomedical targets. SCCs can serve as anticancer agents, act as selective sensors for biologically important analytes, or interact with DNA and proteins. The myriad of possible SCCs and their almost limitless modularity and tunability without significant synthetic penalty suggests that the biological applications of such species will continue along this already promising path.

Heteroleptic cyclometalated iridium(III) complexes supported by triarylborylpicolinate ligand: ratiometric turn-on phosphorescence response upon fluoride binding.

Heteroleptic cyclometalated iridium(III) complexes (C^N)2Ir(Bpic) (4-6) (C^N = dfppy (4), ppy (5), btp (6)) supported by triarylborylpicolinate (Bpic) ancillary ligand were synthesized and characterized. X-ray diffraction study of 5 confirmed N^O chelation of the Bpic ligand to the iridium center forming an (C^N)2Ir-borane conjugate. While the UV/vis absorption bands of 4-6 remained almost unchanged in the low-energy region upon fluoride addition, a ratiometric turn-on phosphorescence response was observed for 4 and 5. In contrast, the phosphorescence of 6 was little affected by fluoride binding. Experimental and theoretical studies suggest that the LUMO in neutral 4 and 5 is dominated by the Bpic ligand, which makes the weakly emissive (3)ML'CT/(3)LL'CT (L = C^N; L' = Bpic) states as the lowest-energy triplet excited state, while the fluoride binding to 4 and 5 induces the highly emissive (3)MLCT/(3)ππ* states centered on the (C^N)2Ir moiety. Thermally induced conversion from the (3)MLCT/(3)ππ* to the (3)ML'CT/(3)LL'CT states is suggested to be responsible for the low-energy weak phosphorescence in 4 and 5.

Deep red phosphorescence of cyclometalated iridium complexes by o-carborane substitution.

Heteroleptic (C(∧)N)2Ir(acac) (C(∧)N = 5-MeCBbtp (5a); 4-BuCBbtp (5b); 5-BuCBbtp (5c); 5-(R)CBbtp = 2-(2'-benzothienyl)-5-(2-R-ortho-carboran-1-yl)-pyridinato-C(2),N, R = Me and n-Bu; 4-BuCBbtp = 2-(2'-benzothienyl)-4-(2-n-Bu-ortho-carboran-1-yl)-pyridinato-C(2),N, acac = acetylacetonate) complexes supported by o-carborane substituted C(∧)N-chelating ligand were prepared, and the crystal structures of 5a and 5b were determined by X-ray diffraction. While 5a and 5c exhibit a deep red phosphorescence band centered at 644 nm, which is substantially red-shifted compared to that of unsubstituted (btp)2Ir(acac) (6) (λem = 612 nm), 5b is nonemissive in THF solution at room temperature. In contrast, all complexes are emissive at 77 K and in the solid state. Electrochemical and theoretical studies suggest that the carborane substitution leads to the lowering of both the HOMO and LUMO levels, but has higher impact on the LUMO stabilization than the HOMO, resulting in the reduction of the triplet excited state energy. In particular, the LUMO stabilization in the 4-substituted 5b is more contributed by carborane than that in the 5-substituted 5a. The solution-processed electroluminescent device incorporating 5a as an emitter displayed deep red phosphorescence (CIE coordinate: 0.693, 0.290) with moderate performance (max ηEQE = 3.8%) whereas the device incorporating 5b showed poor performance, as well as weak luminance.