Intense Red-Blue Luminescence Based on Superfine Control of Metal–Metal Interactions for Self-Assembled Platinum(II) Complexes

A series of assembled Pt^II complexes comprising N-heterocyclic carbene and cyanide ligands was constructed using different substituent groups, [Pt(CN)₂(R-impy)] (R-impyH⁺=1-alkyl-3-(2-pyridyl)-1H-imidazolium, R=Me ( Pt-Me ), Et ( Pt-Et ), ⁱPr ( Pt- ⁱ Pr ), and ^tBu ( Pt- ^t Bu )). All the complexes exhibited highly efficient photoluminescence with an emission quantum yield of 0.51–0.81 in the solid state at room temperature, originating from the triplet metal-metal-to-ligand charge transfer (³MMLCT) state. Their emission colors cover the entire visible region from red for Pt-Me to blue for Pt- ^t Bu . Importantly, Pt- ^t Bu is the first example that exhibits blue ³MMLCT emission. The ³MMLCT emission was proved and characterized based on the temperature dependences of the crystal structures and emission properties. The wide-range color tuning of luminescence using the ³MMLCT emission presents a new strategy of superfine control of the emission color.     

Coherent Vibration and Femtosecond Dynamics of the Platinum Complex Oligomers upon Intermolecular Bond Formation in the Excited State

Femtosecond time-resolved absorption and picosecond time-resolved emission measurements were carried out for highly concentrated aqueous solutions of K₂[Pt(CN)₄] to investigate excited-state dynamics of the [Pt(CN)₄²⁻] oligomers formed with metallophilic interactions. Time-resolved absorption spectra exhibit complicated dynamics that are represented with five time constants. Among them, the 90-ps and 400-ps dynamics were assigned to the S₁ → T₁ intersystem crossing of the trimer and tetramer coexisting in the solution by comparison with the fluorescence decays. Clear oscillations of transient absorption were observed in the first few picoseconds, and the frequency-detected-wavelength 2D analysis revealed that the 135-cm⁻¹ and 65-cm⁻¹ oscillations arise from the Pt–Pt stretch motions of the S₁ trimer and S₁ tetramer, respectively. The obtained time-resolved spectroscopic data provide a clear view of the excited-state dynamics of the [Pt(CN)₄²⁻] oligomers in the femto-/picosecond time region.     

Solvent-Vapor-Induced Reversible Single-Crystal-to-Single-Crystal Transformation of a Triphosphaazatriangulene-Based Metal–Organic Framework

A triphosphaazatriangulene (H₃L) was synthesized through an intramolecular triple phospha-Friedel–Crafts reaction. The H₃L triangulene contains three phosphinate groups and an extended π-conjugated framework, which enables the stimuli-responsive reversible transformation of [Cu(HL)(DMSO)⋅(MeOH)]_n, a 3D-MOF that exhibits reversible sorption characteristics, into (H₃L⋅0.5 [Cu₂(OH)₄⋅6 H₂O] ⋅4 H₂O), a 1D-columnar assembled proton-conducting material. The hydrophilic nature of the latter resulted in a proton conductivity of 5.5×10⁻³ S cm⁻¹ at 95 % relative humidity and 60 °C.     

A Dual-Ligand Porous Coordination Polymer Chemiresistor with Modulated Conductivity and Porosity

Single-ligand-based electronically conductive porous coordination polymers/metal–organic frameworks (EC-PCPs/MOFs) fail to meet the requirements of numerous electronic applications owing to their limited tunability in terms of both conductivity and topology. In this study, a new 2D π-conjugated EC-MOF containing copper units with mixed trigonal ligands was developed: Cu₃(HHTP)(THQ) (HHTP=2,3,6,7,10,11-hexahydrotriphenylene, THQ=tetrahydroxy-1,4-quinone). The modulated conductivity (σ≈2.53×10⁻⁵ S cm⁻¹ with an activation energy of 0.30 eV) and high porosity (ca. 441.2 m² g⁻¹) of the Cu₃(HHTP)(THQ) semiconductive nanowires provided an appropriate resistance baseline and highly accessible areas for the development of an excellent chemiresistive gas sensor.     

A Dual‐Ligand Porous Coordination Polymer Chemiresistor with Modulated Conductivity and Porosity

Single‐ligand‐based electronically conductive porous coordination polymers/metal–organic frameworks (EC‐PCPs/MOFs) fail to meet the requirements of numerous electronic applications owing to their limited tunability in terms of both conductivity and topology. In this study, a new 2D π‐conjugated EC‐MOF containing copper units with mixed trigonal ligands was developed: Cu₃(HHTP)(THQ) (HHTP=2,3,6,7,10,11‐hexahydrotriphenylene, THQ=tetrahydroxy‐1,4‐quinone). The modulated conductivity (σ≈2.53×10^?5 S cm^?1 with an activation energy of 0.30 eV) and high porosity (ca. 441.2 m² g^?1) of the Cu₃(HHTP)(THQ) semiconductive nanowires provided an appropriate resistance baseline and highly accessible areas for the development of an excellent chemiresistive gas sensor.     

Photoluminescent Ferroelastic Molecular Crystals

Ferroelasticity has been reported for several types of molecular crystals, which show mechanical‐stress‐induced shape change under twinning and/or spontaneous formation of strain. Aiming to create materials that exhibit both ferroelasticity and light‐emission characteristics, we discovered the first examples of ferroelastic luminescent organometallic crystals. Crystals of arylgold(I)(N‐heterocyclic carbene)(NHC) complexes bend upon exposure to anisotropic mechanical stress. X‐ray diffraction analyses and stress‐strain measurements on these ferroelastic crystals confirmed typical ferroelastic behavior, mechanical twinning, and the spontaneous build‐up of strain. A comparison with single‐crystal structures of related gold‐NHC complexes that do not show ferroelasticity shed light on the structural origins of the ferroelastic behavior.     

Structure and Electron Transport at Metal Atomic Junctions Doped with Dichloroethylene

The front cover artwork was provided by the group of Prof. Nishino, Tokyo Institute of Technology. The image depicts the investigation of the structure and electron transport of the Au, Ag, Cu, Ni, Fe, and Pd atomic junctions doped with dichloroethylene. Read the full text of the Article at 10.1002/cphc.201900988 .     

Thermodynamic Control of Domain Swapping by Modulating the Helical Propensity in the Hinge Region of Myoglobin

Domain swapping is an exception to Anfinsen's dogma, and more than one structure can be produced from the same amino acid sequence by domain swapping. We have previously shown that myoglobin (Mb) can form a domain‐swapped dimer in which the hinge region is converted to a helical structure. In this study, we showed that domain‐swapped dimerization of Mb was achieved by a single Ala mutation of Gly at position 80. Multiple Ala mutations at positions 81 and 82 in addition to position 80 facilitated dimerization of Mb by stabilization of the dimeric states. Domain swapping tendencies correlated well with the helical propensity of the mutated residue in a series of Mb mutants with amino acids introduced to the hinge region. These findings demonstrate that a single mutation in the hinge loop to modify helical propensity can control oligomer formation, providing new ideas to create high‐order protein oligomers using domain swapping.     

Palladium‐Catalyzed C−H Iodination of Arenes by Means of Sulfinyl Directing Groups

C?H iodination of aromatic compounds has been accomplished with the aid of sulfinyl directing groups under palladium catalysis. The reaction proceeds selectively at the peri‐position of polycyclic aryl sulfoxides or at the ortho‐position of phenyl sulfoxides. The iodination products can be further converted via iterative catalytic cross‐coupling at the expense of the C?I and C?S bonds. Computational studies suggest that peri‐C?H palladation would proceed via a non‐directed pathway, wherein neither of the sulfur nor oxygen atom of the sulfinyl group coordinates to the palladium before and at the transition state.