Multi-electron transfer in photoelectrochemical processes

Simultaneous bidirectional forward and backward electron transfers take place on a light-exited semiconductor particle, even at the same geometric site. The potentials of the electron pathways are different, giving rise to two independent molecular conversion reactions. This type of multi-electron transfer reactions is overviewed and the stepwise unidirectional multi-electron transfer on the excited semiconductor particle is also described.     

Photophysics of Silicon Phthalocyanines in Aqueous Media

Phthalocyanines have been used as photodynamic therapy (PDT) agents because of their uniquely favorable optical properties and high photostability. They have been shown to be highly successful for the treatment of cancer through efficient singlet‐oxygen (¹O₂) production. However, due to their hydrophobic properties, the considerations of solubility and cellular location have made understanding their photophysics in vitro and in vivo difficult. Indeed, many quantitative assessments of PDT reagents are undertaken in purely organic solvents, presenting challenges for interpreting observations during practical application in vivo. With steady‐state and time‐resolved laser spectroscopy, we show that for axial ligated silicon phthalocyanines in aqueous media, both the water:lipophile ratio and the pH have drastic effects on their photophysics, and ultimately dictate their functionality as PDT drugs. We suggest that considering the presented photophysics for PDT drugs in aqueous solutions leads to guidelines for a next generation of even more potent PDT agents.     

Structure–Function Relationships in Unsymmetrical Zinc Phthalocyanines for Dye‐Sensitized Solar Cells

Let it shine! The impact of the anchoring group on photovoltaic performance by a series of phthalocyanine sensitisers (see figure) has been demonstrated.

     

相转移催化合成酯基取代酞菁铜及其光导性能

酞菁配合物的大π键共轭体系使其具有独特的物理化学性能．但酞菁的难溶性,限制了其进一步的研究和应用．Baker等首次制备了可溶性酞菁单分子膜,并将其应用到光电池中;随后,已有大量的相关研究报道．作为常见的可溶性酞菁衍生物,酯基取代酞菁由于含酯基的前体物质高温分解而不能采用直接缩合的方法,     

Visible light-driven acridone catalysis for atom transfer radical polymerization

Acridone as a new kind of visible light photocatalyst has been developed to catalyze metal free atom transfer radical polymerization (ATRP). The photocatalyst possess low excited state potential as can undergo an oxidative quenching pathway to initiate ATRP of vinyl monomers. Kinetic study and light on/off reaction demonstrate the “living”/controlled nature of the polymerization by light. Block copolymers can be achieved by using PMMA as macroinitiator to reinitiate polymerization of other vinyl monomers, which shows highly preserved Br chain-end functionality in the synthesized polymers. Moreover, the polymerization can be conducted under air atmosphere as most photocatalysts need anaerobic condition, which may give inspiration of further application of this kind of photocatalyst.     

Phase transfer catalysis in the chemistry of aliphatic nitrocompounds

The methylation of trinitromethane (TNM) Na-salt under phase transfer catalysis (PTC) conditions was studied in a two-phase system (aqueous solution of TNM Na-salt-CH₃I). The obtained data revealed a relationship between the yield of the methylation product (1,1,1-trinitroethane) and the nature of the phase transfer catalyst and the degree of TNM anion transfer to the organic phase. The kinetic measurements showed that higher efficiency of methylation was achieved under PTC conditions than occurs in a homogeneous reaction due to the fact that the reaction proceeded in the CH₃I medium.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1086–1088, June, 1993.     

Effect of Axial Ligands on the Molecular Configurations,Stability, Reactivity,and Photodynamic Activities of Silicon Phthalocyanines

To demonstrate the effect of axial ligands on the structure–activity relationship, a series of axially substituted silicon phthalocyanines (SiPcs) have been synthesized with changes to the axial ligands. The reactivity of the axial ligand upon shielding by the phthalocyanine ring current, along with their stability, photophysical, and photodynamic therapy (PDT) activities were compared and evaluated for the first time. As revealed by single‐crystal XRD analysis, rotation of the axial ? OMe ligands was observed in SiPc 3 , which resulted in two molecular configurations coexisting synchronously in both the solid and solution states and causing a split of the phthalocyanine α protons in the ¹H NMR spectra that is significantly different from all SiPcs reported so far. The remarkable photostability, good singlet oxygen quantum yield, and efficient in vitro photodynamic activity synergistically show that compound 3 is one of the most promising photosensitizers for PDT.     

相转移催化在杂环化学中的应用

就近几年来相转移催化(PTC)在杂环化学中的应用,包括杂环化合物的合成,杂环化合物的化学修饰及杂环的转变进行了综述。     

Phase transfer catalysis in the chemistry of five-membered nitrogen-containing heterocycles

The methods for synthesis and reactions of five-membered nitrogen-containing heterocycles under the conditions of phase transfer catalysis as well as the application of quaternized heterocycles as phase transfer catalysts are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2115–2121, November, 1995.     

Combining Zinc Phthalocyanines,Oligo(p-Phenylenevinylenes), and Fullerenes to Impact Reorganization Energies and Attenuation Factors

A study on electron transfer in three electron donor-acceptor complexes is reported. These architectures consist of a zinc phthalocyanine (ZnPc) as the excited-state electron donor and a fullerene (C₆₀) as the ground-state electron acceptor. These complexes are brought together by axial coordination at ZnPc. The key variable in our design is the length of the molecular spacer, namely, oligo-p-phenylenevinylenes. The lack of appreciable ground-state interactions is in accordance with strong excited-state interactions, as inferred from the quenching of ZnPc centered fluorescence and the presence of a short-lived fluorescence component. Full-fledged femtosecond and nanosecond transient absorption spectroscopy assays corroborated that the ZnPc ⋅ ⁺-C₆₀ ⋅ ⁻ charge-separated state formation comes at the expense of excited-state interactions following ZnPc photoexcitation. At a first glance, the ZnPc ⋅ ⁺-C₆₀ ⋅ ⁻ charge-separated state lifetime increased from 0.4 to 86.6 ns as the electron donor-acceptor separation increased from 8.8 to 29.1 Å. A closer look at the kinetics revealed that the changes in charge-separated state lifetime are tied to a decrease in the electronic coupling element from 132 to 1.2 cm⁻¹, an increase in the reorganization energy of charge transfer from 0.43 to 0.63 eV, and a large attenuation factor of 0.27 Å⁻¹.     

Kinetics of synthesizing liquid-crystals, 4, 4"-dialkoxybiphenyl by phase transfer catalysis

Reactions of 4,4"-biphenol and bromoalkanes to synthesize 4,4"-dialkoxybiphenyls were carried out under phase-transfer catalysis. Quaternary ammonium salts (QBr) and propansultan (QSO₃) were used as the phase transfer catalysts. Eight liquid crystals including symmetric and asymmetric diethers and the active catalyst (QO(Ph)₂OQ) were produced from the reactions.     

Electrophilic carbon transfer in gold catalysis: synthesis of substituted chromones

Using easily accessible aromatic alkoxy-arylalkynones, we have investigated the gold-catalyzed intramolecular addition of ethers to alkynes, to give easy access to various substituted chromones. This reaction involves the transfer of the ether substituent via a carbodemetallation process. We also noticed a competing isomerization of several starting materials for which we propose a second gold catalyzed mechanism.     

Tuning photoinduced energy- and electron-transfer events in subphthalocyanine-phthalocyanine dyads

A series of subphthalocyanine-phthalocyanine dyads has been prepared by means of palladium-catalyzed cross-coupling reactions between a monoalkynylphthalocyanine and different monoiodosubphthalocyanines. Electronic coupling between the two photoactive units is ensured by a rigid and pi-conjugated alkynyl spacer. In addition, the electronic characteristics of the subphthalocyanine moiety were modulated by the introduction of different peripheral substituents. Cyclic and Osteryoung square-wave voltammetry experiments revealed that the reduction potential of this subunit can be decreased by about 400 mV on going from thioether or no substituents to nitro groups. As a consequence, the energy level of the charge-transfer state could be fine-tuned so as to gain control over the fate of the photoexcitation energy in each subunit. The diverse steady-state and time-resolved photophysical techniques employed demonstrated that, when the charge-transfer state lies high in energy, a quantitative singlet-singlet energy-transfer mechanism from the excited subphthalocyanine to the phthalocyanine takes place. On the contrary, stabilization of the radical pair by lowering the redox gap between electron donor and acceptor results in a highly efficient photoinduced electron-transfer process, even in solvents of low polarity such as toluene (Phi(ET) approximately 0.9). These features, together with the extraordinary absorptive cross section that these molecular ensembles display across the whole UV/Vis spectrum, make them model candidates for application in situations where broadband light sources are needed.     

Synthesis of O-benzyl oximes by combination of phase transfer catalysis and ultrasound irradiation

The reactions of oximes with benzyl bromide catalyzed by benzyldimethyltetradecylammonium chloride are carried out at room temperature for 30–60 min in aqueous sodium hydroxide solution under ultrasound irradiation to offer O-benzyl oxime derivatives in 60–96% yields. In comparison to classical methods, the advantages of the present procedure include short reaction time, high yields and environmental friendliness. __________ Translated from Chinese Journal of Organic Chemistry, 2008, 28(4) (in Chinese)     

相转移催化下二醇类及肟类的选择性间接电氧化

在对Cr(VI)/Cr(III)体系在相转移催化下对醇类的选择性间接电氧化进行了探讨,发现共醇类能被高产率、选择性地氧化为相应的羰基化合物,而非苄醇类则无此效果的基础上,本文是在此基础上,对分子内含有苄醇羟基和另一个非苄醇羟基的二醇类及肟类化合物进行了选择性电氧化的探讨,结果发现,在本实验条件下,共醇羟基能被选择性地氧化为相应的羰基,而分子内共存的非苄醇羟基几乎不受影响;各种肟类化合物也能有选择地氧化裂解为相应的羰基化合物,而不被深度氧化。     

Crystal structure of chiral binaphthol lanthanide complexes and their catalysis in asymmetric transfer hydrogenation of acetophenone

Heterometallic [(THF)₂Na]₃[Ln(R‐Binolate)₃(H₂O)] [Ln = Sm ( 1 ) and Gd ( 2 )] has been synthesized by the reactions of either LnCl₃ or LnBr₃ with 3 equiv. Na(R‐HBinolate) and characterized by X‐ray crystallographic analysis. Structural analyses proposed that 1 and 2 are isomorphous complexes, crystallizing in the hexagonal space group P6₃ with C₃ symmetry. The coordination geometry of the lanthanide ions in 1 and 2 can be best approximated as a mono‐capped triangle antiprism. When complexes 1 and 2 were employed as catalysts in the Meerwein–Ponndorf–Verley (MPV) reactions of acetophenone, the S‐phenylethanol was separated in 94 and 85% enantiomeric excess (e.e.) for 1 and 2 , respectively. Copyright © 2005 John Wiley & Sons, Ltd.     

Highly Efficient Singlet Oxygen Generators Based on Ruthenium Phthalocyanines: Synthesis,Characterization and in vitro Evaluation for Photodynamic Therapy

The synthesis of ruthenium(II) phthalocyanines (RuPcs) endowed with one carbohydrate unit—that is, glucose, galactose and mannose—and a dimethylsulfoxide (DMSO) ligand at the two axial coordination sites, respectively, is described. Two series of compounds, one unsubstituted at the periphery, and the other one bearing eight PEG chains at the isoindole meta-positions, have been prepared. The presence of the axial DMSO unit significantly increases the phthalocyanine singlet oxygen quantum yields, related to other comparable RuPcs. The compounds have been evaluated for PDT treatment in bladder cancer cells. In vitro studies have revealed high phototoxicity for RuPcs unsubstituted at their periphery. The phototoxicity of PEG-substituted RuPcs has been considerably improved by repeated light irradiation. The choice of the axial carbohydrate introduced little differences in the cellular uptake for both series of photosensitizers, but the phototoxic effects were considerably higher for compounds bearing mannose units.     

Synergism and antagonism in phase transfer catalysis

Synergism and antagonism phenomena in phase transfer catalytic reactions have been considered. The factors responsible for the Synergism in the catalysis by an onium salt-crown ether mixture have been determined. Special attention have been paid to quantitative estimation of synergism and antagonism. The influence of addition of water on the rates of the reactions in solid-liquid systems have been discussed.In memory of the 75th anniversary of Member of the Academy of Sciences of Ukrainian SSR L. M. Litvinenko.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2108–2114, November, 1995.