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.

     

Synthesis and Photoproperties of Silicon Phthalocyanines and Silicon Naphthalocyanines

Silicon phthalocyanines and silicon naphthalocyanines, which are two derivatives in the family of hematoporphyrin, have been synthesized to assess their potential as photosensitizers for photodynamic therapy. For these complexes the red shift of their Q-band maximum absorption tends to depend on the nature of the axial substituent. The bimolecular rate coefficients for the interacting between photosensitizer, either SiNC or SiPC, and generated singlet molecular oxygen were determined from the time-resolved emission spectrum of singlet oxygen at 1.27 μm. On the basis of these data the electron-transfer quenching mechanism is discussed in relation to the Marcus model.     

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.     

Phthalocyanines and related macrocycles for multi-electron transfer in catalysis,photochemistry and photoelectrochemistry

At different phthalocyanines and related macrocycles it is shown that one-step, multi-electron transfer and one-step, multi-change of oxidation states occur. At first, the catalytic oxidations of thiols and sulfide in the presence of different Co(II)phthalocyanines are discussed. Thiolates are oxidized to disulfides via a two-electron transfer whereas the reduction of O₂ occurs via a two- or four-electron transfer to H₂O₂ or H₂O. Zn(II) and Al(III)phthalocyanines are efficient sensitizers for the conversion of triplet to singlet dioxygen under illumination with visible light. In the presence of thiolates or sulfides an efficient photo-oxidation to sulfonic acids or sulfate is observed. The oxidation state of sulfur changes from ?2 to +4 or +6, respectively. This process of singlet oxygen reactions finds application in the photodynamic therapy of cancer. The unsubstituted zinc(II)-phthalocyanine as p-type molecular semiconductor can efficienfly reduce O₂ in photoelectrochemical experiments whereas zinc(II)phthalocyanines with electronwithdrawing groups as n-type conductors are active in the photoelectrochemical oxidation of thiols. All processes include multi-electron transfer. The electrocatalytic reduction of CO₂ is investigated at electrodes modified with Co(II)phthalocyanine. In particular, the phthalocyanine in a polyvinylpyridine membrane is active, so the CO₂ is reduced to CO by multi-electron transfer. In addition, two photon excitations of a Mg(II)phthalocyanine are presented and some examples are reviewed.     

Synthesis and Photoinduced Intramolecular Processes of Light‐Harvesting Silicon Phthalocyanine–Naphthalenediimide–Fullerene Connected Systems

Fast moving : A new pentad (see figure) composed of silicon phthalocyanine (SiPc), as electron donor, that is connected with two units of naphthalenediimide (NDI) and fullerene C₆₀, as electron acceptors, undergoes fast and efficient charge‐separation processes via the NDI and SiPc singlet excited states.

     

Proton‐Coupled Electron Transfer Induced by Near‐Infrared Light

A proton‐coupled electron transfer reaction induced by near‐infrared light (>710 nm) has been achieved using a dye that shows intense NIR absorption property and electron/proton‐accepting abilities. The developed system generated long‐lived radical species and showed high reversibility and robustness. Mechanistic investigations suggested that the rate‐determining step of the reaction involves the proton transfer process.     

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.     

Continuous Flow Photochemistry

Due to the narrow width of tubing/reactors used, photochemistry performed in micro‐ and mesoflow systems is significantly more efficient than when performed in batch due to the Beer‐Lambert Law. Owing to the constant removal of product and facility of flow chemical scalability, the degree of degradation observed is generally decreased and the productivity of photochemical processes is increased. In this Personal Account, we describe a wide range of photochemical transformations we have examined using both visible and UV light, covering cyclizations, intermolecular couplings, radical polymerizations, as well as singlet oxygen oxygenations.     

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.     

Photoinduced Electron Transfer‐based Halogen‐free Photosensitizers: Covalent meso‐Aryl (Phenyl,Naphthyl, Anthryl,and Pyrenyl) as Electron Donors to Effectively Induce the Formation of the Excited Triplet State and Singlet Oxygen for BODIPY Compounds

Pristine BODIPY compounds have negligible efficiency to generate the excited triplet state and singlet oxygen. In this report, we show that attaching a good electron donor to the BODIPY core can lead to singlet oxygen formation with up to 58 % quantum efficiency. For this purpose, BODIPYs with meso ‐aryl groups (phenyl, naphthyl, anthryl, and pyrenyl) were synthesized and characterized. The fluorescence, excited triplet state, and singlet oxygen formation properties for these compounds were measured in various solvents by UV/Vis absorption, steady‐state and time‐resolved fluorescence methods, as well as laser flash photolysis technique. In particular, the presence of anthryl and pyrenyl showed substantial enhancement on the singlet oxygen formation ability of BODIPY with up to 58 % and 34 % quantum efficiency, respectively, owing to their stronger electron‐donating ability. Upon the increase in singlet oxygen formation, the fluorescence quantum yield and lifetime values of the aryl‐BODIPY showed a concomitant decrease. The increase in solvent polarity enhances the singlet oxygen generation but decreases the fluorescence quantum yield. The results are explained by the presence of intramolecular photoinduced electron transfer from the aryl moiety to BODIPY core. This method of promoting T₁ formation is very different from the traditional heavy atom effect by I, Br, or transition metal atoms. This type of novel photosensitizers may find important applications in organic oxygenation reactions and photodynamic therapy of tumors.     

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 ( Re₁Pc ) 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 Re₁Pc and Re₂Pc , 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. Re₁Pc represents a promising red-light-driven photoCORM that can be applied in biological environments or therapeutic applications.     

Linking photo- and redoxactive phthalocyanines covalently to graphene

"Green" graphene: For the first time, the covalent attachment of a light-harvesting and electron-donating phthalocyanine to the basal plane of few-layer graphene is reported. Physicochemical characterizations reveal an ultrafast charge separation from the photoexcited phthalocyanine to few-layer graphene followed by a slower charge recombination.     

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.     

取代锌酞菁的合成及光物理性质

取代锌酞菁的合成及光物理性质张先付,许慧君（中国科学院感光化学研究所,北京,１００１０１）关键词取代酞菁,合成,光物理性质,电荷转移癌症的光动力疗法及其机制是目前光医学、光生物学及光化学的前沿课题［１］。临床应用的光疗药物──血卟啉有一些难以克服的致...     

Riboflavin Interactions with Oxygen—A Survey from the Photochemical Perspective

In this short review we provide some insights to the main processes that riboflavin is involved in upon absorption of a photon. We describe riboflavin properties in its interactions with oxygen, comparing them to the properties of some other singlet oxygen sensitizers. Data are provided on riboflavin photosensitizing properties in vivo and in vitro, and its properties as an endogenous singlet oxygen sensitizer are discussed. We additionally report flavin catalytic role in organic synthesis and photochemical reactivity in solutions of riboflavin and some of its derivatives.     

Fluorescence Quenching of Poly[2-methoxy-5-(2''''-ethylhexoxy)-p-phenylene vinylene](MEH-PPV) in Solutions

Introduction Poly(1,4-phenylene vinylene) (PPV) has been the subject of explosive interest in these years. It has poten-tial applications in light-emitting diode, light emitting electrochemical cell and plastic laser.1-4 To improve its solubility and optical properties substituents are intro-duced to the PPV main chain. Poly[2-methoxy-5-(2'-ethylhexoxy)-p-phenylene vinylene] (MEH-PPV) is one of derivatives with alkoxy groups on phenyl rings. It exhibits superior solubility in organic sol…