Porphyrin-Polyoxotungstate Molecular Hybrid as a Highly Efficient, Durable, Visible-Light-Responsive Photocatalyst for Aerobic Oxidation Reactions.

Organic-polyoxometalate (POM) hybrids have recently attracted considerable interest because of their distinctive properties and wide-ranging applications. For the construction of organic-POM hybrids, porphyrins are promising building units owing to their optical properties and reactivity, including strong visible-light absorption and subsequent singlet-oxygen (1O2*) generation. However, the practical utilization of porphyrins as photocatalysts and photosensitizers is often hindered by their own degradation by 1O2*. Therefore, there is a substantial demand for the development of porphyrin-derived photocatalysts with both high efficiency and durability. Herein, we present a porphyrin-polyoxotungstate molecular hybrid featuring a face-to-face stacked porphyrin dimer (I) fastened by four lacunary polyoxotungstates. Hybrid I exhibited remarkable efficiency and durability in photocatalytic aerobic oxidation reactions, and the selective oxidation of various dienes, alkenes, sulfides, and amines proceeded using just 0.003 mol % of the catalyst. Mechanistic investigations suggested that the high activity of I stems from the efficient generation of 1O2*, resulting from the heavy-atom effect of POMs. Furthermore, despite its high efficiency in 1O2* generation compared to free porphyrins, I exhibited superior durability against 1O2*-induced degradation under photoirradiation.

Chiroptical Response Inversion and Enhancement of Room-Temperature Exciton-Polaritons Using 2D Chirality in Perovskites.

Although chiral semiconductors have shown promising progress in direct circularly polarized light (CPL) detection and emission, they still face potential challenges. A chirality-switching mechanism or approach integrating two enantiomers is needed to discriminate the handedness of a given CPL; additionally, a large material volume is required for sufficient chiroptical interaction. These two requirements pose significant obstacles to the simplification and miniaturization of the devices. Here, room-temperature chiral polaritons fulfilling dual-handedness functions and exhibiting a more-than-two-order enhancement of the chiroptical signal are demonstrated, by embedding a 40 nm-thick perovskite film with a 2D chiroptical effect into a Fabry-Pérot cavity. By mixing chiral perovskites with different crystal structures, a pronounced 2D chiroptical effect is accomplished in the perovskite film, featured by an inverted chiroptical response for counter-propagating CPL. This inversion behavior matches the photonic handedness switch during CPL circulation in the Fabry-Pérot cavity, thus harvesting giant enhancement of the chiroptical response. Furthermore, affected by the unique quarter-wave-plate effects, the polariton emission achieves a chiral dissymmetry of ±4% (for the emission from the front and the back sides). The room-temperature polaritons with the strong dissymmetric chiroptical interaction shall have implications on a fundamental level and future on-chip applications for biomolecule analysis and quantum computing.

Two-photon, red light uncaging of alkyl radicals from organorhodium(III) phthalocyanine complexes.

A stepwise two-photon, red light excitation of organorhodium(III) phthalocyanine complexes was found to induce the activation of the axial metal-carbon bond to generate alkyl radicals/aldehydes. The cooperative action of the photouncaging reaction and the photochemical generation of reactive oxygen species were indicated to induce the cell deaths.

Organic deliquescence: organic vapor-induced dissolution of molecular salts.

This report demonstrates organic vapor-induced dissolution of several molecular salts (i.e., organic deliquescence), like water vapor-induced deliquescence. Systematic experiments indicate that appropriate organic deliquescent responses to volatile organic compounds can be designed according to the principle, "like dissolves like". The phenomena will be useful for developing agents to collect various volatile organic compounds.

A Red-Light-Driven CO-Releasing Complex: Photoreactivities and Excited-State Dynamics of Highly Distorted Tricarbonyl Rhenium Phthalocyanines.

A complex comprising one [Re(CO)3 ]+ unit and a phthalocyanine (Pc) ligand (Re1 Pc) is shown to function as a photo-induced CO-releasing molecule (photoCORM) in the presence of O2 and a coordinative solvent under irradiation with red light, which can deeply penetrate living tissues. Transient absorption spectroscopic measurements indicate very short excited-state lifetimes and ultrafast intersystem crossing for Re1 Pc and Re2 Pc, which contains two [Re(CO)3 ]+ units. The excited-state properties are ascribed to efficient spin-orbit coupling and large Franck-Condon factors originating from the complexes' distorted structures, that is, unsymmetric coordination of [Re(CO)3 ]+ unit(s), one of which was confirmed by single-crystal X-ray analysis of a symmetrically substituted Pc with two [Re(CO)3 ]+ units. Re1 Pc represents a promising red-light-driven photoCORM that can be applied in biological environments or therapeutic applications.

Chiral Induction in Buckminsterfullerene Using a Metal-Organic Framework.

Chiral induction is an emerging topic of interest in various areas of chemistry because of its relationship to the elusive mechanism of spontaneous symmetry breaking in nature. Buckminsterfullerene (C60 ) with the shape of a highly symmetric truncated icosahedron has rarely been referred for chiral induction due to the difficult symmetry breaking. In this work, we demonstrate that a chiral metal-organic framework (MOF) can provide a key field for chiral induction. C60 could be incorporated into the chiral nanochannels of the MOF using an in situ self-assembly strategy. The circular dichroism spectra of the resulting nanocomposites showed an intense chiral signal in the absorption region of C60 . Experimental and theoretical studies showed that this unprecedented chiral induction of C60 was attributed to hybridization of the molecular orbitals through a close association with the pore surface of the MOF. Our method can endow highly symmetric achiral compounds with chirality, paving the new way toward fabrication of novel chiral nanomaterials.

Distorted Porphyrins with High Stability: Synthesis and Characteristic Electronic Properties of Mono- and Di-Nuclear Tricarbonyl Rhenium Tetraazaporphyrin Complexes.

Mono- and di-nuclear tricarbonyl Re(I) tetraazaporphyrin complexes (Re1 TAP and Re2 TAP) are investigated and compared with Re(I) phthalocyanine complexes (Re1 Pc and Re2 Pc). Although Re2 Pc is unstable in polar solvents, and easily undergoes demetallation reaction, the coordination of the TAP ligand significantly improves the tolerance toward polar solvents, affording more stability to Re2 TAP. Additionally, the incorporation of [Re(CO)3 ]+ unit(s) and the TAP ligand results in remarkable positive shifts in both oxidation and reduction potentials. Consequently, the more positive oxidation potentials of the ReTAP complexes significantly increase the tolerance toward oxidation, while the reduction potential indicates that Re2 TAP is suitable for a soluble electron acceptor. In contrast to Re1 Pc and Re2 Pc, Re1 TAP and Re2 TAP show unique broad Q bands, which can be attributed to the admixture of the π-π* and metal-to-ligand charge transfer characters, owing to the lowered π orbital energy in the TAP complexes. This study is useful for controlling electronic properties and realizing high stability in Pc analogues.

Novel method for preparing stable near-infrared absorbers: a new phthalocyanine family based on rhenium(i) complexes.

Rational design of near-infrared (NIR) absorbing molecules is crucial for developing photofunctional materials. Here, we synthesized dinuclear and mononuclear Re(i) tricarbonyl phthalocyanine complexes that exhibit a sharp intense Q band in the NIR region. The unsymmetric coordination of electron-deficient metal unit(s) concomitantly produced a remarkable red shift of the Q band and improved the tolerance of the phthalocyanine ring to oxidation. This study presents a simple and effective strategy for the construction of NIR absorbers with high stability.

Direct Observation of the S0 → T2 Transition in Phosphorescent Platinum(II) Octaethylporphyrin, Evidenced by Magnetic Circular Dichroism.

In recent years, the importance of analyzing excited triplet states has increased dramatically because of their relevance in the design and development of photofunctional molecules. Since the second lowest excited triplet (T2) state plays an important role in enhancing the nonradiative intersystem crossing (ISC) process from the lowest excited singlet (S1) state to the lowest excited triplet (T1) state, it is strongly desired to develop direct observation methods for the nonluminescent, short-lived T2 state. In this study, the excited triplet states of platinum(II) octaethylporphyrin (PtOEP), which was used as the first phosphorescent organic light emitting diode and oxygen sensor, are investigated using UV-vis absorption, magnetic circular dichroism, and phosphorescence spectroscopies. At low temperature, in highly concentrated solutions, we observe a distinct Faraday A term for the S0 → T1 transition, as well as for the S0 → T2 transition. The novel spectroscopic methodology applied allows resolution of the excited-state properties of a wide variety of molecular systems.

Molecular ground-state dissociation in the condensed phase employing plasmonic field enhancement of chirped mid-infrared pulses.

Selective bond cleavage via vibrational excitation is the key to active control over molecular reactions. Despite its great potential, the practical implementation in condensed phases have been hampered to date by poor excitation efficiency due to fast vibrational relaxation. Here we demonstrate vibrationally mediated, condensed-phase molecular dissociation by employing intense plasmonic near-fields of temporally-shaped mid-infrared (mid-IR) pulses. Both down-chirping and substantial field enhancement contribute to efficient ladder climbing of the carbonyl stretch vibration of W(CO)6 in n-hexane solution and to the resulting CO dissociation. We observe an absorption band emerging with laser irradiation at the excitation beam area, which indicates that the dissociation is followed by adsorption onto metal surfaces. This successful demonstration proves that the combination of ultrafast optics and nano-plasmonics in the mid-IR range is useful for mode-selective vibrational ladder climbing, paving the way toward controlled ground-state chemistry.

Improved Conditions for the Visible-Light Driven Hydrocarboxylation by Rh(I) and Photoredox Dual Catalysts Based on the Mechanistic Analyses.

The improved catalytic conditions and detailed reaction mechanism of the visible-light driven hydrocarboxylation of alkenes with CO2 by the Rh(I) and photoredox dual catalysts were investigated. The use of the benzimidazoline derivative, BI(OH)H, as a sacrificial electron donor was found to increase the yield of the hydrocarboxylated product by accelerating the reduction process. In addition, the incorporation of the cyclometalated Ir(III) complex as a second photosensitizer with [Ru(bpy)3]2+ photosensitizer also resulted in the promotion of the reduction process, supporting that the catalytic cycle includes two photochemical elementary processes: photoinduced electron and energy transfers.

Role of the immune response in initiating central nervous system regeneration in vertebrates: learning from the fish.

The mammalian central nervous system is not able to regenerate neurons lost upon injury. In contrast, anamniote vertebrates show a remarkable regenerative capacity and are able to replace damaged cells and restore function. Recent studies have shown that in naturally regenerating vertebrates, such as zebrafish, inflammation is a key processes required for the initiation of regeneration. These findings are in contrast to many studies in mammals, where the central nervous system has long been viewed as an immune-privileged organ with inflammation considered one of the key negative factors causing lack of neuronal regeneration. In this review, we discuss similarities and differences between naturally regenerating vertebrates, and those with very limited to non-existing regenerative capacity. We will introduce neural stem and progenitor cells in different species and explain how they differ in their reaction to acute injury of the central nervous system. Next, we illustrate how different organisms respond to injuries by activation of their immune system. Important immune cell types will be discussed in relation to their effects on neural stem cell behavior. Finally, we will give an overview on key inflammatory mediators secreted upon injury that have been linked to activation of neural stem cells and regeneration. Overall, understanding how species with regenerative potential couple inflammation and successful regeneration will help to identify potential targets to stimulate proliferation of neural stem cells and subsequent neurogenesis in mammals and may provide targets for therapeutic intervention strategies for neurodegenerative diseases.

Different developmental histories of beta-cells generate functional and proliferative heterogeneity during islet growth.

The proliferative and functional heterogeneity among seemingly uniform cells is a universal phenomenon. Identifying the underlying factors requires single-cell analysis of function and proliferation. Here we show that the pancreatic beta-cells in zebrafish exhibit different growth-promoting and functional properties, which in part reflect differences in the time elapsed since birth of the cells. Calcium imaging shows that the beta-cells in the embryonic islet become functional during early zebrafish development. At later stages, younger beta-cells join the islet following differentiation from post-embryonic progenitors. Notably, the older and younger beta-cells occupy different regions within the islet, which generates topological asymmetries in glucose responsiveness and proliferation. Specifically, the older beta-cells exhibit robust glucose responsiveness, whereas younger beta-cells are more proliferative but less functional. As the islet approaches its mature state, heterogeneity diminishes and beta-cells synchronize function and proliferation. Our work illustrates a dynamic model of heterogeneity based on evolving proliferative and functional beta-cell states.Βeta-cells have recently been shown to be heterogeneous with regard to morphology and function. Here, the authors show that ß-cells in zebrafish switch from proliferative to functional states with increasing time since ß-cell birth, leading to functional and proliferative heterogeneity.

Visible-Light-Driven Carboxylation of Aryl Halides by the Combined Use of Palladium and Photoredox Catalysts.

A highly useful, visible-light-driven carboxylation of aryl bromides and chlorides with CO2 was realized using a combination of Pd(OAc)2 as a carboxylation catalyst and Ir(ppy)2(dtbpy)(PF6) as a photoredox catalyst. This carboxylation reaction proceeded in high yields under 1 atm of CO2 with a variety of functionalized aryl bromides and chlorides without the necessity of using stoichiometric metallic reductants.

Construction of a visible light-driven hydrocarboxylation cycle of alkenes by the combined use of Rh(i) and photoredox catalysts.

A visible light driven catalytic cycle for hydrocarboxylation of alkenes with CO2 was established using a combination of a Rh(i) complex as a carboxylation catalyst and [Ru(bpy)3]2+ (bpy = 2,2'- bipyridyl) as a photoredox catalyst. Two key steps, the generation of Rh(i) hydride species and nucleophilic addition of π-benzyl Rh(i) species to CO2, were found to be mediated by light.

Infrared vibrational spectroscopy of [Ru(bpy)2(bpm)]2+ and [Ru(bpy)3]2+ in the excited triplet state.

This work involved a detailed investigation into the infrared vibrational spectra of ruthenium polypyridyl complexes, specifically heteroleptic [Ru(bpy)2(bpm)](2+) (bpy = 2,2'-bipyridine and bpm = 2,2'-bipyrimidine) and homoleptic [Ru(bpy)3](2+), in the excited triplet state. Transient spectra were acquired 500 ps after photoexcitation, corresponding to the vibrational ground state of the excited triplet state, using time-resolved infrared spectroscopy. We assigned the observed bands to specific ligands in [Ru(bpy)2(bpm)](2+) based on the results of deuterium substitution and identified the corresponding normal vibrational modes using quantum-chemical calculations. Through this process, the more complex vibrational bands of [Ru(bpy)3](2+) were assigned to normal vibrational modes. The results are in good agreement with the model in which excited electrons are localized on a single ligand. We also found that the vibrational bands of both complexes associated with the ligands on which electrons are little localized appear at approximately 1317 and 1608 cm(-1). These assignments should allow the study of the reaction dynamics of various photofunctional systems including ruthenium polypyridyl complexes.

Revelation of the photoactive species in the photocatalytic dimerization of α-methylstyrene by a dinuclear ruthenium-palladium complex.

A quantum chemical study of the photocatalytic dimerization of α-methylstyrene catalyzed by a dinuclear ruthenium-palladium complex was performed at the DFT/TD-DFT level in order to find the key steps of the catalytic reaction. This study reveals that the second insertion of α-methylstyrene is the rate-determining step and that it proceeds via triplet excited states of an intermediate complex. These excited states have geometries significantly different from that of the reactant, especially within the coordination sphere of the Pd unit. Indeed, one Pd-carbon bond is considerably lengthened, favoring the insertion process. These results open up the possibilities to optimize the process by fine modulation of the catalyst structure.

Syntheses, photophysical properties, and reactivities of novel bichromophoric Pd complexes composed of Ru(II)-polypyridyl and naphthyl moieties.

A series of novel bichromophoric Ru(II) complexes bearing a naphthyl chromophore linked with 2,2'-bipyridyl (bpy) and 2,2'-bipyrimidine (bpm) ligands were synthesized. Complexation with a Pd-alkyl unit led to the formation of bichromophoric Ru-Pd catalysts. The photochemical and electrochemical properties of the newly synthesized compounds were studied. It has been shown that the UV-light energy absorbed at the pendant naphthyl moiety is effectively transferred to the Ru(II) center; this is supported by the observation of metal-to-ligand charge-transfer luminescence through excitation of the naphthyl unit, which is identical to the luminescence observed through visible light excitation. The luminescence lifetime of the complex bearing a naphthyl moiety directly connected to the bpy ligands was lengthened to ca. 1000 ns. When a Pd complex containing the bichromophoric unit with an extended lifetime was used as a catalyst, styrene polymerization under visible or UV light irradiation was observed, in clear contrast to dimerization using other catalysts. These results indicate the formation of an excited-state with a prolonged excited-state lifetime, which promotes an insertion step in preference to the competing ß-H elimination step.