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.     

面向能源领域的石墨烯研究

化石能源枯竭以及地球环境污染已经成为并且在未来相当长一段时期内都将是人类面临的最严峻的危机之一.因此,寻找清洁的替代能源形式、有效的能量存储方式以及高效的能源利用途径是目前科学研究的热点.自从其高质量样品被制备和研究以来,石墨烯一直吸引着全世界科研工作者的兴趣;它的一系列独特的物理化学性质,为其在能源领域的应用提供了无限前景.本文对石墨烯在能源领域的最新研究进展以及其工业化应用作了简要综述,具体内容包括石墨烯材料在以下领域的应用：能源储存器件类,如超级电容器和锂离子电池;能源转化装置类,如燃料电池和太阳能电池.     

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.     

Electrochemistry of graphene: new horizons for sensing and energy storage

Graphene is a new 2D nanomaterial with outstanding material, physical, chemical, and electrochemical properties. In this review, we first discuss the methods of preparing graphene sheets and their chemistry. Following that, the fundamental reasons governing the electrochemistry of graphene are meaningfully described. Graphene is an excellent electrode material with the advantages of conductivity and electrochemistry of sp² carbon but without the disadvantages related to carbon nanotubes, such as residual metallic impurities. We highlight important applications of graphene and graphene nanoplatelets for sensing, biosensing, and energy storage. © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 211–223; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.200900008     

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.

     

Ge‐Mediated Modification in Ta3N5 Photoelectrodes with Enhanced Charge Transport for Solar Water Splitting

Ta₃N₅ is a promising photoanode candidate for photoelectrochemical water splitting, with a band gap of about 2.1 eV and a theoretical solar‐to‐hydrogen efficiency as high as 15.9 % under AM 1.5 G 100 mW cm^?2 irradiation. However, the presently achieved highest photocurrent (ca. 7.5 mA cm^?2) on Ta₃N₅ photoelectrodes under AM 1.5 G 100 mW cm^?2 is far from the theoretical maximum (ca. 12.9 mA cm^?2), which is possibly due to serious bulk recombination (poor bulk charge transport and charge separation) in Ta₃N₅ photoelectrodes. In this study, we show that volatilization of intentionally added Ge (5 %) during the synthesis of Ta₃N₅ promotes the electron transport and thereby improves the charge‐separation efficiency in bulk Ta₃N₅ photoanode, which affords a 320 % increase of the highest photocurrent comparing with that of pure Ta₃N₅ photoanode under AM 1.5 G 100 mW cm^?2 simulated sunlight.     

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.

     

Photoinduced Betaine Generation for Efficient Photothermal Energy Conversion

The conversion of solar energy to thermal, chemical, or electrical energy attracts great attention in chemistry and physics. There has been a considerable effort for the efficient extraction of photons throughout the entire solar spectrum. In this work light energy was efficiently harvested by using a long-lived betaine photogenerated from an acridinium-based electron donor–acceptor dyad. The photothermal energy-conversion efficiency of the dyad is significantly enhanced by simultaneous illumination with blue (420–440 nm) and yellow (>480 nm) light in comparison with the sum of the conversion efficiencies for individual illumination with blue or yellow light. The enhanced photothermal effect is due to the photogenerated betaine, which absorbs longer-wavelength light than the dyad, and thus the dyad–betaine combination is promising for efficient photothermal energy conversion. The mechanisms of betaine generation and energy conversion are discussed on the basis of steady-state and transient spectral measurements.     

Light‐Harvesting Phthalocyanine–Diketopyrrolopyrrole Derivatives: Synthesis,Spectroscopic, Electrochemical,and Photochemical Studies

A new family of light‐harvesting zinc phthalocyanine (ZnPc)–diketopyrrolopyrrole (DPP) hybrids have been synthesized and characterized. The absorption spectral measurements showed that the major absorptions of DPP (450–600 nm) are complementary to those of zinc phthalocyanine (300–400 and 600–700 nm). Therefore, the designed hybrids absorb over a broad range in the visible region. The geometric and electronic structures of the dyads were probed by initio B3LYP/6‐311G methods. The majority of the HOMOs were found to be located on the ZnPc, while the majority of the LUMOs were on the DPP units. The DPP units serve as the antenna, which upon excitation undergo efficient singlet–singlet energy transfer to the attached ZnPc units. The formed singlet ZnPc, in turn, donates its electron to the electron‐deficient DPP forming the low‐lying radical ion pairs ZnPc^.+–DPP^.? (energy=1.44–1.56 eV as calculated from the electrochemical measurements). The excited‐state events were confirmed by using a transient absorption technique in the picosecond–microsecond time range, as well as a time‐resolved emission technique. The rates of energy transfer from the singlet DPP to ZnPc were found to be extremely fast >10¹⁰ s^?1, while the rates of electron transfer from the singlet excited state of ZnPc to DPP were found to be 3.7–6.6×10⁹ s^?1.     

Accumulation of Four Electrons on a Terphenyl (Bis)disulfide

The activation of N₂, CO₂ or H₂O to energy-rich products relies on multi-electron transfer reactions, and consequently it seems desirable to understand the basics of light-driven accumulation of multiple redox equivalents. Most of the previously reported molecular acceptors merely allow the storage of up to two electrons. We report on a terphenyl compound including two disulfide bridges, which undergoes four-electron reduction in two separate electrochemical steps, aided by a combination of potential compression and inversion. Under visible-light irradiation using the organic super-electron donor tetrakis(dimethylamino)ethylene, a cascade of light-induced reaction steps is observed, leading to the cleavage of both disulfide bonds. Whereas one of them undergoes extrusion of sulfur to result in a thiophene, the other disulfide is converted to a dithiolate. These insights seem relevant to enhance the current fundamental understanding of photochemical energy storage.     

Photoinduced Electron and Energy Transfer in Dyads of Porphyrin Dimer and Perylene Tetracarboxylic Diimide

Two compounds containing a porphyrin dimer and a perylene tetracarboxylic diimide (PDI) linked by phenyl ( 1 ) or ethylene groups ( 2 ) are prepared. The photophysical properties of these two compounds are investigated by steady state electronic absorption and fluorescence spectra and lifetime measurements. The ground state absorption spectra reveal intense interactions between the porphyrin units within the porphyrin dimer, but no interactions between the porphyirn dimer and PDI. The fluorescence spectra suggest efficient energy transfer from PDI to porphyrin accompanied by less efficient electron transfer from porphyrin to PDI. The energy transfer is not affected by the dimeric structure of porphyrin or the linkage between the porphyrin dimer and PDI. However, the electron transfer from porphyrin to PDI is significantly affected by either the linkage between the donor and the acceptor or the polarity of the solvents. The dimeric structure of the porphyrin units in these compounds significantly promotes electron transfer in nonpolar, but not in polar solvents.     

Synthesis of azo-conjugated catecholate complexes and their photo- and proton-responses

A new azo-conjugated catecholate ligand, azocat , and its nickel complexes were synthesized, and their physical and chemical properties were investigated. The complex with one azocat shows no obvious photo-response, whereas the compound with two azocat 's causes a little photoisomerization. Both of these novel azo-conjugated catecholate complexes show remarkable proton responses.     

Getting the Most out of Solar Irradiation: Efficient Use of Polychromatic Light for Water Splitting

To increase the fraction of utilizable polychromatic light, a new reactor concept was developed and manufactured by using rapid prototyping technologies. Investigation of the prototypes revealed enhancements of the photocurrent by up to one order of magnitude, when TiO₂ was used as the photoanode in combination with commercially available photovoltaic cells. The reported concept is scalable and an easy transfer to technical scale is expected from a technological as well as an economical perspective. Experimental results underline the conclusion that to achieve efficient overall use of solar irradiation both the material as well as the reactor/process must be considered. Combining these complementary approaches allows largest possible optimization potential. With respect to ongoing research, the concept also breaks ground for the development of catalysts.     

Porphyrin–Phthalocyanine/Pyridylfullerene Supramolecular Assemblies

The synthesis and photophysical properties of several porphyrin (P)–phthalocyanine (Pc) conjugates (P–Pc; 1 – 3 ) are described, in which the phthalocyanines are directly linked to the β‐pyrrolic position of a meso‐tetraphenylporphyrin. Photoinduced energy‐ and electron‐transfer processes were studied through the preparation of H₂P–ZnPc, ZnP–ZnPc, and PdP–ZnPc conjugates, and their assembly through metal coordination with two different pyridylfulleropyrrolidines ( 4 and 5 ). The resulting electron‐donor–acceptor hybrids, which were formed by axial coordination of compounds 4 and 5 with the corresponding phthalocyanines, mimicked the fundamental processes of photosynthesis; that is, light harvesting, the transduction of excited‐state energy, and unidirectional electron transfer. In particular, photophysical studies confirmed that intramolecular energy‐transfer resulted from the S₂ excited state as well as from the S₁ excited state of the porphyrins to the energetically lower‐lying phthalocyanines, followed by an intramolecular charge‐transfer to yield P–Pc^.+ ? C₆₀^.?. This unique sequence of processes opens the way for solar‐energy‐conversion processes.