"Point-Line-Plane-Helix" Binuclear Platinum(II) Complexes: Metal-Induced Chirality, Chirality Self-Sorting, and Chiroptical Properties.

Chirality is a fundamental property of nature, and thus, building novel chiral molecules plays a crucial role in multidisciplinary fields. Herein, we have developed a straightforward approach to effectively incorporate all four types of point, axial, planar, and helical chiralities into a single molecule for the first time. The resultant "point-line-plane-helix" binuclear Pt(II) complexes exhibit multiple chiralities, including not only point and axial chiralities from the bridging ligands but also planar and helical chiralities from metal coordination. The intramolecular π-π and Pt-Pt interactions will restrict intramolecular rotations, thereby stabilizing the metal-induced planar and helical chiralities. Furthermore, enantiopure (R,R,R,Rp,M) or (S,S,S,Sp,P) molecules could be obtained by chirality self-sorting without the use of chiral high-performance liquid chromatography. Their single-crystal, circular dichroism, and circularly polarized luminescence properties are comprehensively investigated, providing unequivocal insights into the design of multiple-chirality materials for related applications.

Metal-Induced Planar Chirality of Soft-Bridged Binuclear Platinum(II) Complexes: 100 % Phosphorescence Quantum Yields, Chiral Self-Sorting, and Circularly Polarized Luminescence.

PtII complexes have attracted a great deal of interest due to their rich phosphorescent properties. However, these square-planar PtII complexes are far more likely to encounter the problems of lack of metal-induced chirality and emission "aggregation-caused quenching". Herein, soft-bridged binuclear PtII complexes bearing metal-induced planar chirality were synthesized and characterized. These soft bridging ligands with smaller conjugated system would help to not only improve solubility for synthesis and enantioseparation but also introduce point chirality from amino acid for highly efficient diastereoselectivity. Furthermore, the intramolecular Pt-Pt distances could be well regulated by soft bridging ligands, and consequently the phosphorescence quantum yield up to 100 % could be achieved by shortening intramolecular Pt-Pt distance for first time. These complexes can be used as emitters in highly efficient solution-processed organic light-emitting diodes.

Iron-Catalyzed C-C Bond Cleavage of Oximes for Direct Coupling of Benzothiazole in Water.

An Fe-catalyzed coupling reaction between oxime ester and benzothiazole is described, which involves C-C bond cleavage of oxime ester via a single-electron transfer process. This iron catalytic system performed in water under mild reaction conditions offers a streamlined strategy to the construction of alkyl nitrile substituted benzothiazole derivatives. Application of this strategy for the synthesis of some key important compounds including 4-heterocyclic-3-arylbutanoic acid is also reported.

Room-Temperature Phosphorescence of Pure Axially Chiral Bicarbazoles.

Ultralong room-temperature phosphorescence (RTP) is greatly important in a series of applications, but obtaining RTP from metal-free organic materials is still an enormous challenge due to the spin-forbidden nature of triplet excitons. Because of its electron-rich nature and easy derivatization, carbazole (Cz) is widely used to build organic RTP and thermally activated delayed fluorescence (TADF) materials. However, Liu et al. (Nat. Mater. 2021, 20, 175) recently demonstrated that the RTP of Cz is induced by charge traps of its isomeric impurity in commercial sources. Here, on the basis of the classical El-Sayed rule and the recently discovered intersystem crossing promotion principles (twisted structure and charge transfer), we designed and prepared highly pure (>99.9%) (R/S)-octahydro-binaphthyl-based bicarbazoles (BiCz) for high-performance RTP (ΦP = 23%; τp = 1.09 s). Interestingly, BiCz exhibited photoactivated TADF and RTP in isolated and aggregated states, respectively, and thus would be an efficient tool for rejuvenating Cz-based RTP.

Selective Activation of Unstrained C(O)-C Bond in Ketone Suzuki-Miyaura Coupling Reaction Enabled by Hydride-Transfer Strategy.

A Rh(I)-catalyzed ketone Suzuki-Miyaura coupling reaction of benzylacetone with arylboronic acid is developed. Selective C(O)-C bond activation, which employs aminopyridine as a temporary directing group and ethyl vinyl ketone as a hydride acceptor, occurs on the alkyl chain containing a ß-position hydrogen. A series of acetophenone products were obtained in yields up to 75%.

Highly Phosphorescent Planar Chirality by Bridging Two Square-Planar Platinum(II) Complexes: Chirality Induction and Circularly Polarized Luminescence.

Chiral organometallic complexes have demonstrated many potential and practical applications. However, building metal-induced chirality for square-planar complexes still remains a big challenge, because their 2D planar molecular structures are usually superimposable on their mirror images. Herein, we report a straightforward and efficient way to achieve a novel kind of planar chirality by constructing 3D double-layer molecular structures. When the achiral ligand 1,3,4-oxadiazole-2-thiol (OXT) was used to bridge two square-planar complexes, a pair of racemic R/S planar-chiral binuclear Pt(II) complexes was obtained, which could be separated by chiral high-performance liquid chromatography (HPLC). Moreover, enantiopure R,R,R or S,S,S complexes could be prepared by the use of chiral (R)-/(S)-binaphthalene-derived OXT ligands in 99% diastereoselectivity without the use of chiral HPLC. The binaphthalene groups help to ensure good solubility and a smooth amorphous thin film morphology but have little effect on the photophysical properties. The resultant complexes display strong orange-red and near-infrared phosphorescence with quantum yields of up to 83.4% and can be applied as emitters in highly efficient solution-processed organic light-emitting diodes to achieve luminance, luminance efficiency, external quantum efficiency, and an asymmetry factor of up to 3.22 × 104 cd m-2, 28.7 cd A-1, 14.3%, and 2.0 × 10-3, respectively. With a comprehensive consideration of EL efficiency and the asymmetry factor, this is the best performance among Pt(II) complex based circularly polarized OLEDs. Therefore, this work provides a new and simple strategy to build planar chirality for chiroptical and circularly polarized luminescence applications.

Axially Chiral Bis-Cycloplatinated Binaphthalenes and Octahydro-Binaphthalenes for Efficient Circularly Polarized Phosphorescence in Solution-Processed Organic Light-Emitting Diodes.

A new series of axially chiral binuclear Pt(II) complexes with bridging ligands of binaphthalenes and octahydro-binaphthalenes and auxiliary ligands of ß-diketones were designed and prepared. These complexes, identified by spectral and electrochemical methods and single-crystal X-ray diffraction, emit an orange-red phosphorescence with a quantum yield up to 21% and 70% in solution and solid, respectively, due to the effect of steric hindrance from bridging ligands and the 2,3-position extension of chiral axis planes. They can be used as emitters in solution-processed organic light-emitting diodes to achieve luminance efficiency, asymmetry factor, and external quantum efficiency up to 5.4 cd A-1, 3.0 × 10-3, and 3.1%, respectively. Moreover, the essential relationships between their chemical structures and luminescence quantum efficiency and asymmetry factor are discussed, which affords explicit insights for designing circularly polarized luminescent materials and devices.

Ultralow-Molecular-Weight Stimuli-Responsive and Multifunctional Supramolecular Gels Based on Monomers and Trimers of Hydrazides.

The simpler, the better. A series of simple, neutral and ultralow-molecular-weight (MW: 140-200) hydrazide-derived supramolecular gelators have been designed and synthesized in two straightforward steps. For non-conjugated cyclohexane-derived hydrazides, their monomers can self-assemble to form gels through intermolecular hydrogen bonds and dipole-dipole interactions. Significantly, conjugated phthalhydrazide can self-aggregate into planar and circular trimers through intermolecular hydrogen bonds and then self-assemble to form gels through intermolecular π-π stacking interactions. It is interesting that these simple gelators exhibit unusual properties, such as self-healing, multi-response fluorescence, and visual and selective recognition of chiral (R)/(S)-1,1'-binaphthalene-2,2'-diamine and S2- through much different times of gel re-formation and blue-green color change, respectively. These results underline the importance of supramolecular gels and extend the scope of supramolecular gelators.

Rhodium-catalyzed annulative coupling of N-aryl-2-aminopyridine and propargylic amine via selective C-C and C-H bond activation.

A Rh(iii)-catalyzed/Cu(ii)-mediated cascade reaction between N-aryl-2-aminopyridine and propargylic amine has been developed. Selective C(sp2)-H bond activation and C(sp)-C(sp3) cleavage occurred during the reaction, which was followed by a cyclization reaction to provide an unprecedented synthetic route to form 1,2-disubstituted indoles in yields up to 85%.

Reversible Chromatic Change of Supramolecular Gels for Visual and Selective Chiral Recognition of Histidine.

In the present work, a chemical reaction has been performed for supramolecular gels to achieve multiple-stimuli-responsive smart soft materials. Simple chiral binaphthalene-based receptors can condense with histidine (His) to yield a Schiff base, which would help to achieve visual chiral recognition of unprotected l/d-His through gel formation along with specific selectivity toward 20 amino acids. Through intermolecular hydrogen bonds, the resultant Schiff base molecules assemble with excess His molecules to form three-dimensional (3D) networks of metastable cross-linked nanospheres and stable nanofibers in EtOH/water and MeOH/water, respectively. Significantly, this condensation reaction exhibits unique reversible and chromatic phenomena between sol-gel phase transitions in EtOH/water, which provide a way to design chemical reaction-based multivisual-change supramolecular gels for sensing and switching applications.

Rhodium-Catalyzed Pyridine N-Oxide Assisted Suzuki-Miyaura Coupling Reaction via C(O)-C Bond Activation.

A rhodium-catalyzed Suzuki-Miyaura coupling reaction via C(O)-C bond activation to form 2-benzoylpyridine N-oxide derivatives is reported. Both the C(O)-C(sp2) and C(O)-C(sp3) bond could be activated during the reaction with yields up to 92%. The N-oxide moiety could be employed as a traceless directing group, leading to free pyridine ketones.

Synthesis of 2-Arylindoles by Rhodium-Catalyzed/Copper-Mediated Annulative Coupling of N-Aryl-2-aminopyridines and Propargyl Alcohols via Selective C-H/C-C Activation.

A versatile rhodium-catalyzed/copper-mediated C-H/C-C activation and cascade annulation reaction was described to form 2-arylindole derivatives. Highly selective C-C bond cleavage of γ-substituted tert-propargyl alcohols occurred, together with pyridine-directed ortho C(sp2)-H bond activation, affording a series of 2-arylindoles with yields up to 90%. Subsequent derivations were smoothly conducted to access polyfunctionalized 2-arylindoles, illustrating the potential applications of this method.

A simple and visual approach for enantioselective recognition through supramolecular gels with specific selectivity.

Simple (S)- or (R)-1,1'-binaphthalene-2,2'-diol-3-carbaldehyde was found to enantioselectively self-assemble to form a gel or solution with one enantiomer of chiral amines, 1,1'-binaphthalene-2,2'-diamine, through intermolecular hydrogen bond, HH, π-π stacking, and chirality-induced interactions. The enantioselective recognition is visual and highly selective with little interference from similar organic compounds and common cations and anions.

1D-helical platinum(ii) complexes bearing metal-induced chirality, aggregation-induced red phosphorescence, and circularly polarized luminescence.

A series of binuclear cyclometalated Pt(ii) complexes with the bridge ligand of binaphthyl quinoline were synthesized and characterized. Owing to the restriction of intramolecular motions in chiral binaphthyl linkers, the complexes exhibited two unusual metal-induced chiral components and aggregation-induced red phosphorescence. The (R,R,R)/(S,S,S) enantiopure complexes that were confirmed by X-ray diffraction, circular dichroism spectra, time-dependent density functional theory calculations, and circularly polarized luminescence did not require purification by chiral high-performance liquid chromatography and could yield unique 1D M or P hierarchical helices of helices via intermolecular noncovalent interactions. Moreover, it is the first time that racemization-induced phosphorescence enhancement has been observed.

Fluorescent ZnII Chemosensor Mediated by a 1,8-Naphthyridine Derivative and It's Photophysical Properties.

One of the greatest challenges in using fluorescent chemosensors for highly selective and sensitive transition-metal ions is finding an efficient and simple method for its synthesis. In this study, a highly efficient fluorescence chemosensor for ZnII was developed from N-Boc-L-proline modified 1,8-naphthyridine. The fluorescence intensity of the chemosensor was increased significantly only in the presence of ZnII ion which provided a perceived color change for rapid visual sensing, while other metal ions showed fluorescence quenching or little changes. It was worth noting that the chemosensor L distinguished ZnII from CdII commonly having similar properties. The solvent effect and possible bonding mode for fluorescence enhancement have been also discussed. Results of this study indicated that the Boc-group in l-proline significantly improved the sensitivity and selectivity for ZnII detection performance, as confirmed by comparison experiments and time dependent-density functional theory (TD-DFT) calculations.

Palladium-catalyzed C(carbonyl)-C bond cleavage of amides: a facile access to phenylcarbamate derivatives with alcohols.

A sulfur-containing auxiliary enabled palladium-catalyzed C(carbonyl)-C bond activation of amides was reported to form phenylcarbamate derivatives with alcohols. Both alkyl and benzyl alcohols could be employed well with yields up to 85%. Derivations from phenylcarbamates to ureas and thiocarbamates illustrated the potential applications of this sequential C-C cleavage/C-O coupling reaction.

Unusual Circularly Polarized and Aggregation-Induced Near-Infrared Phosphorescence of Helical Platinum(II) Complexes with Tetradentate Salen Ligands.

A series of chiral and helical PtII -Salen complexes with 1,1'-binaphthyl linkers were synthesized and characterized. Owing to the restriction of intramolecular motions of central 1,1'-binaphthyls, the complexes exhibit unusual near-infrared aggregation-induced phosphorescence (AIP). The (R)/(S) enantiopure complexes were characterized by X-ray diffraction, circular dichroism spectra, time-dependent density functional theory calculations, and circularly polarized luminescence (CPL). The present work explores the use of tetradentate ligands that can be easily prepared from commercially available enantiopure compounds, and the subsequent preparation of stable CPL-active square planar PtII complexes with AIP effect that may have interest in many applications.

Nonconjugated Fluorescent Molecular Cages of Trinuclear Fluoroborate Complexes with Salicylaldehyde-Based Schiff Base Ligands.

Fluorescent organic materials are commonly π-conjugated planar molecules. In the present work, however, we report a novel class of nonconjugated fluorescent molecular cages of trinuclear fluoroborate complexes (nine samples) with salicylaldehyde-based Schiff base ligands. Owing to the stress from lone pair electrons of N atom in the triethylamine bridge, these B(III) complexes exhibit unusual enantiomers with a tripodlike side-single-opening structure. They emit blue, green, and red emission with large Stokes shifts (up to 159 nm) and high fluorescence quantum yields in both solution (up to 0.24) and solid state (up to 0.25), which might contribute to their strong intramolecular hydrogen bonds and weak intermolecular and intramolecular π-π interactions. Combining their advantages of nonconjugation and biocompatibility, these flexible complexes have potential applications in living cell imaging and anion hosts. We have examined the inherent relationships between their chemical structures and emission properties and afforded a new stage for the design of nonconjugated fluorescent fluoroborate complexes.

A Class of Multiresponsive Colorimetric and Fluorescent pH Probes via Three Different Reaction Mechanisms of Salen Complexes: A Selective and Accurate pH Measurement.

We report a class of multiresponsive colorimetric and fluorescent pH probes based on three different reaction mechanisms including cation exchange, protonation, and hydrolysis reaction of K(I), Ca(II), Zn(II), Cu(II), Al(III), and Pd(II) Salen complexes. Compared with traditional pure organic pH probes, these complex-based pH probes exhibited a much better selectivity due to the shielding function of the filled-in metal ion in the complex. Their pH sensing performances were affected by the ligand structure and the central metal ion. This work is the first report of "off-on-on'-off" colorimetric and fluorescent pH probes that possess three different reaction mechanisms and should inspire the design of multiple-responsive probes for important analytes in biological systems.

Correction: Fluorescent metal ion chemosensors via cation exchange reactions of complexes, quantum dots, and metal-organic frameworks.

Correction for 'Fluorescent metal ion chemosensors via cation exchange reactions of complexes, quantum dots, and metal-organic frameworks' by Jinghui Cheng, et al., Analyst, 2015, DOI: 10.1039/c5an01398d.