Synthesis of arylsulfanyl-subphthalocyanines and their ring expansion reaction

For dye-sensitized solar cells, phthalocyanines require strong absorption of far-red light between 700 and 850 nm because of their high electron transfer efficiency. Nevertheless phthalocyanines lack of affinity to basal plats, they inhibit utilization as dye-sensitized solar cell photosensitizer. Then, subphthalocyanines are used as precursors to prepare asymmetric 3:1 type phthalocyanines using a ring-enlargement technique to give affinity to basal plates. As subphthalocyanines having arylsulfanyl substituents used as a precursor, asymmetric phthalocyanines are expected to have good affinity to basal plates. Spectroscopic properties and electron transfer abilities to synthesize non-peripheral arylsulfanyl-subphthalocyanines were estimated. In addition to prepare as trial, asymmetric 3:1 type phthalocyanine, hexakis[(4-methylphenyl)thio]phthalocyanine, was synthesized from corresponding subphthalocyanine.

Syntheses of near infrared absorbed phthalocyanines to utilize photosensitizers

Phthalocyanines have become of major interest as functional colorants for various applications. In order to use various applications especially photosensitizers, the absorption maxima called Q-band of phthalocyanines are required to be shifted to the near infrared region. Substituted phthalocyanine analog alkylbenzopiridoporphyrazins, especially zinc bis(1,4-didecylbenzo)-bis(3,4-pyrido)porphyrazine, and toroidal-shaped phthalocyanines having aminoamine dendric side chains such as toroidal zinc poly(aminoamine)phthalocyanine dendrons were synthesized. Phthalocyanines of two types reportedly use photosensitizers for photodynamic therapy of cancer. The respective efficacies of photodynamic therapy of cancer for zinc bis(1,4-didecylbenzo)-bis(3,4-pyrido)porphyrazine and its regioisomers were estimated using laser-flash photolysis. The capability of using photodynamic therapy for toroidal zinc poly(aminoamine)phthalocyanine dendrons was assessed using a cancer cell culture. Both phthalocyanines were suitable for the use as a photosensitizer as photodynamic therapy of cancer. Then, non-peripheral thioaryl substituted phthalocyanines, 1,4,8,11,15,18,22,25-octakis(thioaryl)phthalocyanines, such as 1,4,8,11,15,18,22,25-octakis(thiophenylmethyl)phthalocyanines, 1,4,8,11,15,18,22,25-octakis(thiophenylmethoxy)phthalocyanines, and 1,4,8,11,15,18,22,25-octakis(thiophenyl tert-butyl)phthalocyanines were also synthesized in order to develop next- generation photovoltaic cells and/or dye-sensitized solar cells. Non-peripheral substituted 1,4,8,11,15,18,22,25-octakis(thioaryl)phthalocyanines exhibited a Q-band in the near infrared region. Electrochemical measurements were performed on the above-mentioned 1,4,8,11,15,18,22,25-octakis(thioaryl)phthalocyanines described above to examine their electron transfer abilities and electrochemical mechanisms. The compounds 1,4,8,11,15,18,22,25-octakis(thioaryl)phthalocyanines are anticipated to be appropriate materials for use in the next generation of photovoltaic cells.

Photoelectrochemical characterization of electrodepositedZnOthin films sensitized by octacarboxymetallophthalocyanine derivatives

Hybrid thin films of crystalline zinc oxide ( ZnO ) modified by different octacarboxymetallophthalocyanines (MOCPc) were prepared by the readsorption method. Homogeneously blue or green thin films were formed. The photoelectrochemical characteristics of the electrodes were studied by time-resolved photocurrent measurements. Zinc(II) 2,3,9,10,16,17,23,24-octacarboxyphthalocyanine ( ZnOCPc ) showed considerably large quantum efficiency in sensitization of ZnO , one of the highest quantum efficiencies obtained so far with phthalocyanine-type sensitizers on nanocrystalline ZnO films.

Symmetrically and unsymmetrically substituted carboxy phthalocyanines as sensitizers for nanoporousZnOfilms

The photoelectroectrochemical studies of water soluble octacarboxylated oxotitanium (OTiOCPc) , zinc (ZnOCPC) , hydroxyaluminium ((OH)AlOCPc) , dihydroxysilicon ((OH)2SiOCPc) , hydroxygallium (OHGaOCPc) and low symmetry zinc monocarboxy (ZnMCPc) phthalocyanines were performed. The dyes were adsorbed to nanoporous ZnO electrodeposited in the presence of eosin Y as structure directing agent (SDA) on FTO substrates by refluxing or soaking the films in a solution containing the dye of interest such that a full surface coverage was achieved. High external (IPCE) and internal (APCE) quantum efficiencies of up to 50.6% and 96.7% were achieved for the OTiOCPc complex. There was a lower overall cell efficiency for cells sensitized with phthalocyanines containing hydroxyl as axial ligand ZnO/(OH)2SiOCPc , ZnO/(OH)GaOCPc and (OH)AlOCPc because of strong aggregation on the surface of the electrodes. To further suppress dye aggregation, the zinc complex of a new monocarboxylated phthalocyanine sensitizer with bulky naphtho side groups (ZnMCPc) was employed. Among the studied sensitizers, ZnMCPc gave the highest overall cell efficiency of phthalocyanine electrodeposited on ZnO of η = 0.48%.

Nanostructured hybrid ZnO thin films for energy conversion

We report on hybrid films based on ZnO/organic dye prepared by electrodeposition using tetrasulfonated copper phthalocyanines (TS-CuPc) and Eosin-Y (EoY). Both the morphology and porosity of hybrid ZnO films are highly dependent on the type of dyes used in the synthesis. High photosensitivity was observed for ZnO/EoY films, while a very weak photoresponse was obtained for ZnO/TS-CuPc films. Despite a higher absorption coefficient of TS-CuPc than EoY, in ZnO/EoY hybrid films, the excited photoelectrons between the EoY levels can be extracted through ZnO, and the porosity of ZnO/EoY can also be controlled.

Surface functionalization of ZnO nanotetrapods with photoactive and electroactive organic monolayers

Two strategies have been explored for organic functionalizations of ZnO nanotetrapods via anchoring groups of carboxylate and phosphonate. With these methods, oleyl chains were assembled on the surfaces of the ZnO nanotetrapods, significantly enhancing their solubility in nonpolar solvents, such as chloroform and toluene. The surface functionalization strategies have been extended to electroactive and photoactive molecules such as protoporphyrin and C(60) on the ZnO nanotetrapods. The surface-modified ZnO nanotetrapods were characterized comprehensively, revealing a uniform, covalently linked monolayer assembled on the surface. This work opens a broad perspective for the application of the organically functionalized nanotetrapods in optoelectronics and biomedicine.

Photoelectrochemical properties of alternating multilayer films composed of titania nanosheets and Zn porphyrin

Alternating multilayer films composed of titania nanosheets and Zn porphyrins were prepared by use of a previously reported Langmuir-Blodgett film-transfer method in order to fabricate photoelectrochemical devices. Closely packed titania nanosheet monolayers on indium tin oxide (ITO), mica, and quartz surfaces strongly adsorbed cationic [5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrinatozinc]4+ (ZnTMPyP4+) by electrostatic interactions. The alternating deposition process afforded nanometer-scale multilayer films with the following structure: solid surface/(titania nanosheet/ZnTMPyP4+)n (n is the number of layers). The multilayer films were characterized by various physical measurements, including AFM, XRD, and UV-visible spectra. The visible-light irradiation of this multilayer film on an ITO electrode in the presence of triethanolamine as an electron donor yielded an anodic photocurrent. The action spectrum was consistent with the absorption spectrum of ZnTMPyP4+, which indicates that the photoexcitation of ZnTMPyP4+ is responsible for the photocurrent generation. However, the photocurrent density decreased with an increasing number of layers, which indicates that the harvesting of photoexcited electrons vertically through the titania nanosheets in the ITO/(titania nanosheet/ZnTMPyP4+)n structure was not efficient. To overcome this problem, the use of a lateral interlayer connection to all of the titania nanosheets with Ag paste was examined. As a result, a dramatic improvement in the photocurrent density was obtained. Thus, for efficient photocurrent generation with the titania nanosheet-ZnTMPyP4+ composite material, the lateral connection to all of the titania nanosheet layers is effective.

Dependence of the photoelectrochemical performance of sensitised ZnO on the crystalline orientation in electrodeposited ZnO thin films

The influence of the crystal orientation in porous crystalline films of ZnO electrodeposited on the photoelectrochemical characteristics of the films is studied. For differently oriented ZnO thin films following removal of the respective structure-directing agent (SDA) and adsorption of a sensitiser, time-resolved photocurrent measurements, intensity modulated photocurrent spectroscopy (IMPS), intensity modulated photovoltage spectroscopy (IMVS) and current-voltage curves were measured in acetonitrile-based electrolytes containing I(3)(-)/I(-) as the redox electrolyte. The crystal orientation has a significant influence on the charge transport across such films and hence is reflected in the observed electrode kinetics. Films originally grown in the presence of, e.g., Coumarin 343 as a SDA, showed a significantly faster response to illumination. Increased electron diffusion coefficients and diffusion lengths were calculated from the results of IMPS and IMVS, caused by a faster electron movement in the films. Implications of these findings on further improvements of sensitised ZnO films prepared by electrochemical deposition are discussed.