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.

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.

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.

(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.

Syn and Anti Metal Complexes of 24π Antiaromatic Bis(Dicarbonylrhodium(I))Dithiaamethyrin.

From the reaction of sterically less hindered tetrapropyl[24]dithiaamethyrin(1.0.0.1.0.0) 5, with [Rh(CO)2 Cl]2 , a unique anti form of the bis(dicarbonylrhodium(I)) complex (6-anti), where two rhodium ions are on the opposite faces of the macrocyclic ligand, was isolated for the first time in 12% yield along with the corresponding syn isomer (6-syn, 61% yield). These structures were characterized in detail by single-crystal X-ray structure analysis. Compound 6-syn exhibited a bowl-shaped structure with the two rhodium atoms separated by a distance of ∼4.5 Å. In contrast, 6-anti contained a wave-shaped macrocycle with a distance of ∼5.3 Šbetween the two rhodium atoms. Furthermore, the 1 H nuclear magnetic resonance spectra and density functional theory calculation results revealed that 6-anti had a stronger paratropic ring current and a more planar structure than 6-syn. The isolation of both 6-anti and 6-syn enabled detailed discussion of the structure-property relationship.

Numerical Study of Triplet Dynamics in Organic Semiconductors Aimed for the Active Utilization of Triplets by TADF under Continuous-Wave Lasing.

The limitation of lasing duration less than nanosecond order has been a major problem for realizing organic solid-state continues-wave (CW) lasers and organic semiconductor laser diodes. Triplets accumulation under CW excitation has been well recognized as a critical inhibiting factor. To overcome this issue, the utilization of thermally activated delayed fluorescence (TADF) emitters is a promising mechanism because of efficient reverse intersystem crossing. Herein, we model the triplet accumulation processes under lasing and propose the active utilization of TADF for lasing based on our simulation analysis. We used the rate constants experimentally determined from the optical properties of a boron difluoride curcuminoid fluorophore showing both TADF and lasing. We demonstrate that the intersystem crossing efficiency is gradually increased after the convergence of relaxation oscillation, i.e., terminating laser oscillation. In addition, we found that when the reverse intersystem crossing rate is close to the intersystem crossing rate, CW lasing becomes dominant.

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.

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.

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.

Detrimental Effect of Unreacted PbI2 on the Long-Term Stability of Perovskite Solar Cells.

Excess/unreacted lead iodide (PbI2 ) has been commonly used in perovskite films for the state-of-the-art solar cell applications. However, an understanding of intrinsic degradation mechanisms of perovskite solar cells (PSCs) containing unreacted PbI2 has been still insufficient and, therefore, needs to be clarified for better operational durability. Here, it is shown that degradation of PSCs is hastened by unreacted PbI2 crystals under continuous light illumination. Unreacted PbI2 undergoes photodecomposition under illumination, resulting in the formation of lead and iodine in films. Thus, this photodecomposition of PbI2 is one of the main reasons for accelerated device degradation. Therefore, this work reveals that carefully controlling the formation of unreacted PbI2 crystals in perovskite films is very important to improve device operational stability for diverse opto-electronic applications in the future.

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.

Luminescence of mononuclear Pt(ii) complexes with glycolate: external stimuli-induced excimer emission changes to oligomer emissions.

The emission properties and external stimuli-induced emission changes of novel mononuclear platinum(ii) complexes [PtII(4R2bpy)(gl)] (R = H (1), Me (2), tBu (3); 4R2bpy: 4,4'-disubstituted-2,2'-bipyridine; Hgl-: glycolate) were investigated. In solution, all complexes showed orange (λem: 617-623 nm) and green (λem: 488-495 nm) emissions at room temperature and 77 K, respectively, and the emission change is caused by a rigid chromic effect. X-ray crystallography of a red-emitting yellow trihydrate crystal of 1 (1R; λem: 663 nm) and an orange-emitting yellow anhydrate crystal of 3 (3O; λem: 560 nm) revealed the presence of weak π-π interactions between 4R2bpy moieties. When 1R was cooled to 153 K, the emission gradually turned to yellow (λem: 550 nm) owing to the restriction of inter-complex contacts after excitation. Exposing 1R to MeOH vapor rendered yellow-emitting yellow anhydrate crystals (1Y; λem: 558 nm), with the color remaining almost unchanged. Heating 1R gave orange-emitting orange anhydrate crystals (1O; λem: 597 nm). Consequently, the dehydration processes turn an excimer emission of 1R into two types of oligomer emissions (1Y and 1O). A green-emitting yellow 3.5 hydrate crystalline powder of 2 (2G; λem: 531 nm) was reversibly converted to an orange-emitting orange anhydrate powder (2O; λem: 564 nm) upon heating and exposure to H2O vapor, and the behavior is derived from switching between the monomer and an oligomer states. The crystal 3O exhibited an oligomer emission without responsiveness to external stimuli.

A water-soluble cyclometalated iridium(iii) complex for pH sensing based on aggregation-induced enhanced phosphorescence.

The novel water-soluble monoanionic Ir(iii) complex Na[Ir(ppy)2(SB-COO)] (2; Hppy = phenylpyridine; HSB-COOH = 4-carboxylanilinesalicylaldehyde Schiff base), which was obtained by the reaction of the novel Ir(iii) complex [Ir(ppy)2(SB-COOH)] (1) with NaOEt, in its aqueous solution, showed hydrogen ion (H+)-responsive aggregation-induced enhanced phosphorescence (AIEP). Both these complexes exhibited very weak and relatively strong emissions in solution and solid states, respectively. The pH-responsiveness of 2 was evaluated from its emission spectra in aqueous solution in the pH range of 8.7-1.8. Above pH 6, 2 showed weak emission with a maximum at 508 nm. Upon decreasing the pH to 4.7, AIEP with a bathochromic shift to 618 nm was induced by the aggregation of 1, whereby the intensity at 618 nm was increased approximately by 50-fold compared to that at pH 6.0. This enhancement is due to restrictions of the geometrical changes in the six-membered chelate ring of the ancillary ligand (Ir-N-C-C-C-O-) and of the intramolecular rotations in the excited state. The enhanced luminescence originates from spin-forbidden metal-to-ligand-ligand charge transfer (3MLLCT). Below pH 2.8, the emission intensity decreased owing to the decrease in the population of the emissive complex 1 upon dissociation of the ancillary ligand from the Ir(ppy)2 unit.

The Relation of Phase-Transition Effects and Thermal Stability of Planar Perovskite Solar Cells.

A power conversion efficiency of over 20% has been achieved in CH3NH3PbI3-based perovskite solar cells (PSC), however, low thermal stability associated with the presence of a phase transition between tetragonal and cubic structures near room temperature is a major issue that must be overcome for future practical applications. Here, the influence of the phase transition on the thermal stability of PSCs is investigated in detail by comparing four kinds of perovskite films with different compositions of halogen atoms and organic components. Thermally stimulated current measurements reveal that a large number of carrier traps are generated in solar cells with the perovskite CH3NH3PbI3 as a light absorber after operation at 85 °C, which is higher than the phase-transition temperature. Electrochemical impedance spectroscopy measurements further exclude effects of a possible morphology change on the formation of carrier traps. These carrier traps are detrimental to the thermal stability. The thermogravimetric analysis does not show a decomposition for any of the materials in the temperature range relevant for operation. The perovskite alloys do not have this phase transition, resulting in effectively suppressed formation of carrier traps. PSCs with improved thermal stability under the standard thermal cycling test are demonstrated.

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.

Safe and rapid development of capillary electrophoresis for ultratrace uranyl ions in radioactive samples by way of fluorescent probe selection for actinide ions from a chemical library.

After the serious nuclear accident at the Fukushima Daiichi Nuclear Power Plant caused by the Great East Japan Earthquake in 2011, the development of feasible, safe, and highly sensitive analytical methods (in terms of low levels of radiation exposure and radioactive waste generation) for radioactive samples, especially actinide (An) ions, represents an important challenge. Here we propose a methodology for selecting appropriate emissive probes for An ions with very low consumption and emission of radioactivity by capillary electrophoresis-laser-induced fluorescence detection (CE-LIF), using a small chemical library of probes with eight different chelating moieties. It was found that the emissive probe L1, which possesses the tetradentate chelating moiety 1,10-phenanthroline-2,9-dicarboxylic acid (PDA), was suitable for detecting uranyl ions. The detection limit for the uranyl-L1 complex using CE-LIF combined with dynamic ternary complexation and on-capillary concentration techniques was determined to be 2.9 × 10-12 M (0.7 ppt). No interference from the large excess of matrix metal ions was observed. This method was successfully applied to real radioactive liquid samples collected from nuclear facilities, including the Fukushima Daiichi Nuclear Power Plant. This strategy not only permitted the development of a safe and rapid analytical method but also provided insight into the coordination chemistry of An ion complexes. Specifically, the PDA structure provided substantial kinetic inertness to its uranyl complex; the formation of a ternary complex between uranyl-L1 and carbonate was revealed; and unusual interactions were observed between the π-electron systems of uranyl and the phenanthroline ring, which stabilized the uranyl-PDA interaction.