Stable room-temperature continuous-wave lasing in quasi-2D perovskite films.

Organic-inorganic lead halide quasi-two-dimensional (2D) perovskites are promising gain media for lasing applications because of their low cost, tunable colour, excellent stability and solution processability1-3. Optically pumped continuous-wave (CW) lasing is highly desired for practical applications in high-density integrated optoelectronics devices and constitutes a key step towards electrically pumped lasers4-6. However, CW lasing has not yet been realized at room temperature because of the 'lasing death' phenomenon (the abrupt termination of lasing under CW optical pumping), the cause of which remains unknown. Here we study lead halide-based quasi-2D perovskite films with different organic cations and observe that long-lived triplet excitons considerably impede population inversion during amplified spontaneous emission and optically pumped pulsed and CW lasing. Our results indicate that singlet-triplet exciton annihilation is a possible intrinsic mechanism causing lasing death. By using a distributed-feedback cavity with a high quality factor and applying triplet management strategies, we achieve stable green quasi-2D perovskite lasers under CW optical pumping in air at room temperature. We expect that our findings will pave the way to the realization of future current-injection perovskite lasers.

High Myristic Acid in Glycerolipids Enhances the Repair of Photodamaged Photosystem II under Strong Light.

Cyanobacteria inhabit areas with a broad range of light, temperature and nutrient conditions. The robustness of cyanobacterial cells, which can survive under different conditions, may depend on the resilience of photosynthetic activity. Cyanothece sp. PCC 8801 (Cyanothece), a freshwater cyanobacterium isolated from a Taiwanese rice field, had a higher repair activity of photodamaged photosystem II (PSII) under intense light than Synechocystis sp. PCC 6803 (Synechocystis), another freshwater cyanobacterium. Cyanothece contains myristic acid (14:0) as the major fatty acid at the sn-2 position of the glycerolipids. To investigate the role of 14:0 in the repair of photodamaged PSII, we used a Synechocystis transformant expressing a T-1274 encoding a lysophosphatidic acid acyltransferase (LPAAT) from Cyanothece. The wild-type and transformant cells contained 0.2 and 20.1 mol% of 14:0 in glycerolipids, respectively. The higher content of 14:0 in the transformants increased the fluidity of the thylakoid membrane. In the transformants, PSII repair was accelerated due to an enhancement in the de novo synthesis of D1 protein, and the production of singlet oxygen (1O2), which inhibited protein synthesis, was suppressed. The high content of 14:0 increased transfer of light energy received by phycobilisomes to PSI and CP47 in PSII and the content of carotenoids. These results indicated that an increase in 14:0 reduced 1O2 formation and enhanced PSII repair. The higher content of 14:0 in the glycerolipids may be required as a survival strategy for Cyanothece inhabiting a rice field under direct sunlight.

Possible Roles of Transition Metal Cations in the Formation of Interstellar Benzene via Catalytic Acetylene Cyclotrimerization.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous interstellar molecules. However, the formation mechanisms of PAHs and even the simplest cyclic aromatic hydrocarbon, benzene, are not yet fully understood. Recently, we reported the statistical and dynamical properties in the reaction mechanism of Fe+-catalyzed acetylene cyclotrimerization, whereby three acetylene molecules are directly converted to benzene. In this study, we extended our previous work and explored the possible role of the complex of other 3d transition metal cations, TM+ (TM = Sc, Ti, Mn, Co, and Ni), as a catalyst in acetylene cyclotrimerization. Potential energy profiles for bare TM+-catalyst (TM = Sc and Ti), for TM+NC--catalyst (TM = Sc, Ti, Mn, Co, and Ni), and for TM+-(H2O)8-catalyst (TM = Sc and Ti) systems were obtained using quantum chemistry calculations, including the density functional theory levels. The calculation results show that the scandium and titanium cations act as efficient catalysts in acetylene cyclotrimerization and that reactants, which contain an isolated acetylene and (C2H2)2 bound to a bare (ligated) TM cation (TM = Sc and Ti), can be converted into a benzene-metal-cation product complex without an entrance barrier. We found that the number of electrons in the 3d orbitals of the transition metal cation significantly contributes to the catalytic efficiency in the acetylene cyclotrimerization process. On-the-fly Born-Oppenheimer molecular dynamics (BOMD) simulations of the Ti+-NC- and Ti+-(H2O)8 complexes were also performed to comprehensively understand the nuclear dynamics of the reactions. The computational results suggest that interstellar benzene can be produced via acetylene cyclotrimerization reactions catalyzed by transition metal cation complexes.

Cyclometalated Platinum(II) Complexes in a Cis-N,N Configuration: Photophysical Properties and Isomerization to Trans Isomers.

Synthesis, isomerization, and photophysical properties of novel cis-N,N-cyclometalated complexes [Pt(C∧N)(l-Phe)] (C∧N = benzoquinolinate (1), phenylpyridinate (2), 2-(p-tolyl)pyridinate (3), and 1-phenylpyrazolate (4); l-Phe- = l-phenylalaninate) are reported herein. In solution, the cis forms of the complexes isomerize to their trans forms via an associative mechanism. This cis/trans isomerism barely influences the absorption and luminescence properties of the complexes in solution, except for a characteristic absorption at approximately 340 nm in the absorption spectra of the cis complexes that is not observed for the trans complexes. Interestingly, the cis complexes are spontaneously assembled in a crystalline phase and show bathochromic absorption and emission colors compared with those of the corresponding trans isomers, which are aggregated in an amorphous phase. cis-1 and cis-2 demonstrate hypsochromic luminescence mechanochromism. The influence of the geometrical isomerism on the photophysical properties and the isomerization mechanism are supported by density functional theory calculations.

Spin-inversion mechanisms in O2 binding to a model heme complex revisited by density function theory calculations.

Spin-inversion mechanisms in O2 binding to a model heme complex, consisting of Fe(II)-porphyrin and imidazole, were investigated using density-functional theory calculations. First, we applied the recently proposed mixed-spin Hamiltonian method to locate spin-inversion structures between different total spin multiplicities. Nine spin-inversion structures were successfully optimized for the singlet-triplet, singlet-quintet, triplet-quintet, and quintet-septet spin-inversion processes. We found that the singlet-triplet spin-inversion points are located around the potential energy surface region at short Fe-O distances, whereas the singlet-quintet and quintet-septet spin-inversion points are located at longer Fe-O distances. This suggests that both narrow and broad crossing models play roles in O2 binding to the Fe-porphyrin complex. To further understand spin-inversion mechanisms, we performed on-the-fly Born-Oppenheimer molecular dynamics calculations. The reaction coordinates, which are correlated to the spin-inversion dynamics between different spin multiplicities, are also discussed.

o-Azophenylboronic Acid-Based Colorimetric Sensors for d-Fructose: o-Azophenylboronic Acids with Inserted Protic Solvent Are the Key Species for a Large Color Change.

Many boronic acid-based chemosensors for saccharides have been developed; however, their detection mechanisms have seldom been studied. In this study, we synthesized 10 o-azophenylboronic acid derivatives (azoBs) and conducted a fundamental study on the reactivity and the sensing mechanism of azoBs, which undergoes a large color change, e.g., from red to yellow, upon a reaction with saccharides. Their pH-independent formation constants were determined by spectrophotometric titration and then converted to the conditional formation constant K' at pH 7.4. A linear free energy relationship was established between log K' and the pKa of azoB. 11B NMR measurements indicate that in aprotic solvents, azoB forms a trigonal planar structure, while in protic solvents, it forms a quasi-tetrahedral structure (azoB-ROH) with a protic solvent molecule (ROH) inserted between the boronic acid moiety and the azo group. In addition, UV-vis spectroscopic studies showed that the color change during the reaction between azoB and d-fructose in ROH was caused by the release of the ROH from azoB-ROH by d-fructose. Based on the findings in this study, we proposed a guideline for designing an azoB-based chemosensor that exhibits high reactivity toward saccharides and a sufficient color change to allow for the visual detection of saccharides.

Observation of the First Spin Crossover in an Iron(II) Complex with an S6 Coordination Environment: Tris[bis(N,N-diethylamino)carbeniumdithiocarboxylato]iron(II) Hexafluorophosphate.

For the first time, the spin-crossover (SCO) phenomenon has been observed in an FeII -S6 system in a tris(chelate)-type iron(II) complex with a zwitterionic sulfur donor bidentate, bis(N,N-diethylamino)carbeniumdithiocarboxylate (EtL), [FeII (EtL)3 ](PF6 )2 (1), as synthesized by the reaction of a precursor complex [FeII (CH3 CN)6 ](PF6 )2 with EtL. In the solid state, the high-spin (HS) d6 state at ambient temperature and the low-spin (LS) d6 state at temperatures lower than approximately 240 K were evidenced by magnetic measurements with SQUID and Mössbauer spectra in the temperature range 4-290 K. X-ray analyses of the crystals at various temperatures disclosed that the distorted trigonal prismatic coordination environments essentially do not change; however, contraction of Fe-S distances by approximately 10 % (0.22 Å), ordering of alkyl groups in EtL and PF6 - counteranions, and formation of significant intermolecular S⋅⋅⋅S interactions between adjacent molecules (average distances of 3.59 Å) take place during the transition from the HS to the LS state. A large decrease in the volume of the formula unit (78.1 Å3 ) might be responsible for the large activation barrier, thereby resulting in a slow phase transition upon cooling.

Chromism of Tartrate-Bridged Clamshell-like Platinum(II) Complex: Intramolecular Pt-Pt Interaction-Induced Luminescence Vapochromism and Intermolecular Interactions-Triggered Thermochromism.

A novel luminescent clamshell-like platinum(II) complex with rac-tartrate, rac-[{PtII(4Me2bpy)}2(µ-tart)] (Pt2; 4Me2bpy: 4,4'-dimethyl-2,2'-bipyridine; tartH22-: tartrate), was synthesized, and its vapo-, thermo-, and solvatochromic behavior was studied. The complex was isolated in four crystal forms, namely, Pt2·4H2O (color under ambient light: yellow, λem = 573 nm, intramolecular Pt···Pt separation: 3.55 Å), Pt2·4MeOH (red, 650 nm, 3.33 Å), anhydrate Pt2 (red, no luminescence, 3.70 Å), and Pt2·2H2O (orange, 595 nm, 3.60 Å). Vapo- and heat-responsive crystal-to-crystal phase transitions were observed by time- and/or temperature-dependent powder X-ray diffraction, and the molecular and crystal structures of the above crystal forms were determined by either single-crystal X-ray crystallography or Rietveld refinement of powder X-ray diffraction. Vapor diffusion of MeOH to Pt2·4H2O induced a reversible phase transition to Pt2·4MeOH. This structural transformation significantly changed the intramolecular Pt-Pt interactions, affecting the absorption and emission colors. Accordingly, the luminescence chromism originates from alternation of the luminescent nature between a triplet metal-ligand-to-ligand charge-transfer state (3(MLtart)LbpyCT) of Pt2·4H2O and a triplet metal-metal-to-ligand charge-transfer state (3MMLbpyCT) of Pt2·4MeOH. Heating Pt2·4H2O induced a phase transition to anhydrate Pt2, and under atmospheric conditions, anhydrate Pt2 transformed spontaneously to Pt2·2H2O. Vapor diffusion of H2O to Pt2·2H2O caused reconstruction of Pt2·4H2O. The thermochromism originates from changes in the intermolecular interactions between stacked complexes. The solvatochromism was evaluated using the Kamlet-Taft solvatochromic equation, the acceptor number, and the ET(30) scale for the solvent, and the hydrogen-bond acidity of the solvent contributed significantly to the solvent-dependent absorption properties.

Change in Luminescence Induced by Solution-Mediated Phase-Transition of Cyclometalated Platinum(II) Complex with Isoquinoline Carboxylate.

Changes in luminescence due to solution-mediated phase transition (SMPT) and crystal-to-crystal phase transitions of a novel cyclometalated platinum(II) complex with isoquinoline-1-carboxylate (Iq-1-COO-) [Pt(bzq)(Iq-1-COO)] (bzq-: benzoquinolinate) were studied experimentally and theoretically. Recrystallization of the complex allowed three crystal forms depending on the solvent: red polymorph RDMF (λemi = 689 nm), yellow polymorph YDMSO (λemi = 641 nm), and red pseudopolymorph RBCHCl3 (λemi = 721 nm). Crystals of RDMF in the DMF solution at room temperature showed SMPT to yellow crystals YDMF (λemi = 627 nm), in which RDMF first dissolved partly into the solution, and then the dissolved complex crystallized as YDMF. RBCHCl3 exhibited crystal-to-crystal phase transitions to RDMF and YDMF by being heated to 150 °C and stored in atmospheric conditions, respectively. Molecular structures of each of the four crystal forms, analyzed by X-ray crystallography, showed different planarities because of the dihedral angles between the bzq- and Iq planes being 3.15, 4.80, 8.35, and 17.7° for RBCHCl3, RDMF, YDMSO, and YDMF, respectively. The planar complexes in RDMF and RBCHCl3 constructed dimers through intermolecular Pt-Pt and π-π interactions, whereas the distorted complexes in YDMF and YDMSO remained as monomers. Density functional theory (DFT) calculations, which reveal the relation between the molecular structure and thermodynamic stability, suggest that the SMPT is triggered by thermodynamic transformation from the metastable planar structure to the stable distorted structure. The intradimer interactions in RDMF and RBCHCl3 induced red-shifts in the absorption and emission colors from those of YDMF and YDMSO; thus, the photophysical properties of RBCHCl3 and RDMF originate from the MMLIqCT state in contrast with the MLIqCT/LbzqLIqCT character for YDMF and YDMSO. DFT and time-dependent DFT (TD-DFT) calculations in the ground and excited states provide insight into the structural, electronic, and optical properties.

Preparation of polypseudorotaxanes composed of cyclodextrin and polymers in microspheres.

We prepared polypseudorotaxanes (PPRXs) composed of cyclodextrin (CyD) and polyethylene glycol (PEG) inside microspheres (MSs) by an emulsifying process using polypropylene glycol (PPG) that shows temperature-dependent hydrophilicity changes; PPG is hydrophobic at high temperatures but hydrophilic at low temperatures. An aqueous solution of CyD and PEG was dispersed as droplets in PPG at 60°C then cooled to 0°C to allow water of droplets to transfer into PPG. On removal of water in the droplets, CyD and PEG were left behind as a CyD/PEG PPRX inside the solid-state MSs. Examination of α-, ß-, and γ-CyD revealed that α-CyD was suitable for the formation of PPRX containing PEG in this MS preparation procedure. Interestingly, a new PPRX composed of α-CyD and PPG was formed in the α-CyD MSs when they were prepared in the absence of PEG from the aqueous solution of α-CyD. This MS fabrication procedure can control the size and shape of PPRX particles, and will contribute to the production of new types of CyD inclusion complexes.

An ortho-rhom-bic polymorph of N (1),N (4)-diphenyl-3,6-bis-(phenyl-imino)-cyclo-hexa-1,4-diene-1,4-di-amine.

A new ortho-rhom-bic polymorph of the title compound, C30H24N4, with a density of 1.315 Mg m(-3), has been obtained. The mol-ecule is centrosymmetric with the centroid of the cyclo-hexa-1,4-diene ring located on an inversion center. The two unique benzene rings are almost perpendicular to each other [dihedral angle = 86.70 (6)°] and are oriented at dihedral angles of 30.79 (5) and 68.07 (5)° with respect to the central cyclo-hexa-diene ring. In the crystal, π-π stacking is observed between the central cyclo-hexa-1,4-diene-1,4-di-amine unit and a phenyl ring of a neighboring mol-ecule [centroid-centroid distance = 3.7043 (7) Å]. The crystal structure of the triclinic polymorph [Ohno et al. (2014 ▶). Acta Cryst. E70, o303-o304] showed chains running along the b-axis direction through weak C-H⋯π inter-actions.

N (1),N (4)-Diphenyl-3,6-bis-(phenyl-imino)-cyclo-hexa-1,4-diene-1,4-di-amine.

In the title compound, C30H24N4, the central benzo-quinonedi-imine moiety is approximately planar, with a maximum deviation of 0.044 (14) Å. The four terminal phenyl rings are twisted by 44.95 (11), 54.90 (10), 44.98 (10) and 50.68 (11)° with respect to the mean plane the benzo-quinonedi-imine unit. In the crystal, mol-ecules are linked by weak C-H⋯π inter-actions into supra-molecular chains running along the b-axis direction.

Preferential behavior on donating atoms of an ambidentate ligand 2-methylisothiazol-3(2H)-one in its metal complexes.

Five metal complexes of 2-methylisothiazol-3(2H)-one (MIO), [Co(III)(NH3)5(MIO)](3+), [Ru(II)(NH3)5(MIO)](2+), [Ru(III)(NH3)5(MIO)](3+), [Pt(II)Cl3(MIO)](-), and trans-[U(VI)O2(NO3)2(MIO)2], were synthesized, and their structures were determined by single-crystal X-ray crystallography. MIO is an ambidentate ligand and coordinates to metal centers through its oxygen atom in the cobalt(III), ruthenium(III), and uranium(VI) complexes and through its sulfur atom in the ruthenium(II) and platinum(III) complexes. This result suggests that MIO shows preferential behavior on its donating atoms. We also studied the electron-donor abilities of the oxygen and sulfur atoms of MIO. Various physical measurements on the conjugate acid of MIO and the MIO complexes allowed us to determine an acid dissociation constant (pKa) and donor number (DN) for the oxygen atom of MIO and Lever's electrochemical parameter (EL) and a relative covalency parameter (kL) for the sulfur atom.

Di-µ-acetato-κ(4) O:O'-µ-oxido-κ(2) O:O'-bis-[cis-(2,2'-bipyridine-κ(2) N,N')-trans-(pyridine-κN)ruthenium(III)] bis-(hexa-fluoridophosphate).

The hemerythrin-type dinuclear title complex, [Ru2(CH3COO)2O(C10H8N2)2(C5H5N)2](PF6)2, consists of two Ru(III) ions with a six-coordinate octa-hedral geometry, bridged by an oxide and two acetate ligands, with a bidentate 2,2'-bipyridine ligand and a pyridine ligand bonding at terminal positions. The Ru-Ru distance and Ru-O-Ru angle are 3.2838 (3) Šand 121.79 (7)°, respectively, and the average Ru-N(pyridine) bond length is 2.164 (8) Å. Several C-H⋯F, C-H⋯O and C-H⋯N inter-actions generate a three-dimensional network in the crystal structure. π-π stacking inter-actions [centroid-centroid distance = 3.6389 (3) Å] between inversion-related 2,2'-bipyridine rings are also observed.

cis-Dichloridobis(ethyl methyl sulfide-κS)oxidovanadium(IV).

The mononuclear title complex, [VCl2O(C3H8S)2], features a V(IV)=O double bond [1.5845 (15) Å] in an overall trigonal-bipyramidal coordination environment defined by two Cl(-) and the S atoms of two (CH3CH2)(CH3)S ligands. In the crystal, pairs of mol-ecules form centrosymmetric dimers via C-H⋯O hydrogen bonds between the methyl C-H group and the oxidovanadium O atom of a neighbouring mol-ecule.

(31E,32Z,71E,72Z)-4,8-Bis(3,5-di-chloro-phen-yl)-14,33,53,73-tetra-propyl-11H,32H,51H,72H-1,5(2,5),3,7(5,2)-tetra-pyrrola-2,6(2,5)-di-thiophena-cyclo-octa-phane.

Purple crystals of the title compound, C50H44Cl4N4S2 were obtained from the reaction of 2,5-bis-(4-propyl-1H-pyrrol-2-yl)thio-phene and 3,5-di-chloro-benzaldehyde in the presence of tri-fluoro-acetic acid for 3 h and subsequent addition of p-chloranil. The macrocycle in the title compound can be described as a highly planar structure wthe the average deviation of the 32 macrocyclic atoms from the least-squares plane being 0.0416 Å. Its mol-ecular conformation is stabilized by two intra-molecular N-H⋯N bonds and a three-dimensional network is formed by C-H⋯π inter-actions.

Bromocyclization of Alkenoic Thioester and Access to Functionalized Sulfur-Heterocycles.

Although oxygen, nitrogen, and carbon have been extensively studied as nucleophilic elements in the halocyclization of alkenes, sulfur-based nucleophiles are relatively unexplored. Herein, we investigated bromocyclization chemistry involving unsaturated thioesters, with a focus on their use as potential S-nucleophiles. We developed a bromocyclization method that uses alkenoic thioesters and N-bromoacetamide (NBA) to form cyclic bromosulfides. The resulting 5-exo products are labile and can be used in various nucleophilic substitution reactions.

Acylated plastoquinone is a novel neutral lipid accumulated in cyanobacteria.

Although cyanobacteria do not possess bacterial triacylglycerol (TAG)-synthesizing enzymes, the accumulation of TAGs and/or lipid droplets has been repeatedly reported in a wide range of species. In most cases, the identification of TAG has been based on the detection of the spot showing the mobility similar to the TAG standard in thin-layer chromatography (TLC) of neutral lipids. In this study, we identified monoacyl plastoquinol (acyl PQH) as the predominant molecular species in the TAG-like spot from the unicellular Synechocystis sp. PCC 6803 (S.6803) as well as the filamentous Nostocales sp., Nostoc punctiforme PCC 73102, and Anabaena sp. PCC 7120. In S.6803, the accumulation level of acyl PQH but not TAG was affected by deletion or overexpression of slr2103, indicating that acyl PQH is the physiological product of Slr2103 having homology with the eukaryotic diacylglycerol acyltransferase-2 (DGAT2). Electron microscopy revealed that cyanobacterial strains used in this study do not accumulate lipid droplet structures such as those observed in oleaginous microorganisms. Instead, they accumulate polyhydroxybutyrate (PHB) granules and/or aggregates of alkane, free C16 and C18 saturated fatty acids, and low amounts of TAG in the cytoplasmic area, which can be detected by staining with a fluorescent dye specific to neutral lipids. Unlike these lipophilic materials, acyl PQH is exclusively localized in the membrane fraction. There must be DGAT2-like enzymatic activity esterifying de novo-synthesized C16 and C18 fatty acids to PQH2 in the thylakoid membranes.

Synthesis and luminescence properties of substituted benzils.

Photophysical properties of benzil (1,2-diphenylethane-1,2-dione) and its derivatives in the crystal state have recently attracted much attention. However, the study of substituted benzils has mostly been limited to para-substituted derivatives, which did not induce a significant effect on the emission wavelength compared to pristine benzil. The effects of ortho- and meta-substituents on the photophysical properties in the crystal state have not been investigated so far. Our recently developed organocatalytic pinacol coupling of substituted benzaldehydes allowed us to prepare various ortho-, meta-, and para-substituted benzil derivatives and to investigate their luminescence properties. Ortho- and meta-substituents affected the electronic states of benzils in the crystal state, resulting in differences in their luminescence properties. The luminescence wavelength and type, i.e., phosphorescence or fluorescence, were altered by these substituents. Fast self-recovering phosphorescence-to-phosphorescence mechanochromism by the para-CF3 substituent at room temperature was also discovered.

Di-µ-chlorido-µ-(dimethyl sulfide)-bis-{dichlorido[(dimethyl selenide-κSe)(dimethyl sulfide-κS)(0.65/0.35)]niobium(III)}(Nb-Nb).

The dinuclear compound, [Nb(2)Cl(6)(C(2)H(6)S)(1.7)(C(2)H(6)Se)(1.3)], features an Nb(III)=Nb(III) double bond [2.6878 (5) Å]. The mol-ecule lies on a twofold rotation axis that passes through the middle of this bond as well as through the bridging dimethyl sulfide ligand. The Nb(III) ion exists in an octa-hedral coordination environment defined by two terminal and two bridging Cl atoms, and (CH(3))(2)Se/(CH(3))(2)S ligands. The (bridging) ligand lying on the twofold rotation axis is an ordered (CH(3))(2)S ligand, whereas the terminal ones on a general position are a mixture of (CH(3))(2)Se and (CH(3))(2)S ligands in a 0.647 (2):0.353 (2) ratio (the methyl C atoms are also disordered).