Dieter Wöhrle

Singlet oxygen quantum yields of different photosensitizers in polar solvents and micellar solutions

The singlet oxygen luminescence method and the photochemical methods using 1,3-diphenylisobenzofuran (DPBF) or bilirubin ditaurate (BDT) as chemical quenchers were employed to determine the single oxygen quantum yields (ΦΔ) of different phthalocyanines and tris(2,2″-bipyridyl)ruthenium(II) dichloride in dimethylformamide (DMF) or aqueous micellar solution of 0.1 M CTAC (cetyltrimethylammonium chloride). Additionally, a perylenetetracarboxylic acid diimide derivative was examined in DMF. In a series of tetrasulfonated phthalocyanines (PTS) the following order was found: ZnPTS > GaPTS > AlPTS ≈ H2PTS > CoPTS. In general, the singlet oxygen quantum yields are higher in DMF than in 0.1 M CTAC/H2O. The results obtained with the photochemical systems are comparable with those obtained by the photophysical method. The photochemical DPBF method results in absolute values of ΦΔ. However, in micellar solution, chain reactions occur when DPBF is used as chemical quencher in the photo-oxidative process. This problem ...

Chromophores in porous silicas and minerals: preparation and optical properties

Abstract Various synthesis strategies for the preparation of chromophores in porous silicas and minerals like zeolites, zeolite analogues and clays are described focusing on soft procedures like the sol–gel technique, microwave-assisted crystallization inclusion, and deposition in solution in combination with the Langmuir–Blodgett technique. The mild preparation methods protect sensitive dye molecules from chemical degradations. The influences (i) of the chemical properties of the mineral hosts, e.g., polarity and acidity, and (ii) of their spatial constraints on the guest molecules, i.e., their organized arrangement and photophysical properties, are demonstrated exemplarily.

Dendrimer-activated solid supports for nucleic acid and protein microarrays.

The generation of chemically activated glass surfaces is of increasing interest for the production of microarrays containing DNA, proteins, and low‐molecular‐weight components. We here report on a novel surface chemistry for highly efficient activation of glass slides. Our method is based on the initial modification of glass with primary amino groups using a protocol, specifically optimized for high aminosilylation yields, and in particular, for homogeneous surface coverages. In a following step the surface amino groups are activated with a homobifunctional linker, such as disuccinimidylglutarate (DSG) or 1,4‐phenylenediisothiocyanate (PDITC), and then allowed to react with a starburst dendrimer that contains 64 primary amino groups in its outer sphere. Subsequently, the dendritic monomers are activated and crosslinked with a homobifunctional spacer, either DSG or PDITC. This leads to the formation of a thin, chemically reactive polymer film, covalently affixed to the glass substrate, which can directly be used for the covalent attachment of amino‐modified components, such as oligonucleotides. The resulting DNA microarrays were studied by means of nucleic acid hybridization experiments using fluorophor‐labeled complementary oligonucleotide targets. The results indicate that the novel dendrimer‐activated surfaces display a surface coverage with capture oligomers about twofold greater than that with conventional microarrays containing linear chemical linkers. In addition, the experiments suggest that the hybridization occurs with decreased steric hindrance, likely a consequence of the long, flexible linker chain between the surface and the DNA oligomer. The surfaces were found to be resistant against repeated alkaline regeneration procedures, which is likely a consequence of the crosslinked polymeric structure of the dendrimer film. The high stability allows multiple hybridization experiments without significant loss of signal intensity. The versatility of the dendrimer surfaces is also demonstrated by the covalent immobilization of streptavidin as a model protein.

Efficient Near-IR Sensitization of Nanocrystalline TiO2 Films by Zinc and Aluminum Phthalocyanines

Several zinc(II) and aluminum(III) phthalocyanines substituted by carboxylic acid and sulfonic acid groups were anchored to nanocrystalline TiO2 films. By irradiation with visible light the photovoltaic behavior of the electrodes containing LiI/LiI3/propylene carbonate electrolyte was measured. Most efficient results were found using zinc(II) 2,9,16,23-tetracarboxyphthalocyanine, with a current conversion efficiency at 700 nm approaching 45%. It is shown that electron injection into TiO2 occurs from the excited singlet state of the phthalocyanine derivatives. High stability of the cell performance under continuous irradiation was found.

Photo-oxidation of phenol and monochlorophenols in oxygen-saturated aqueous solutions by different photosensitizers

The photo-oxidation of phenol and 2-, 3- and 4-monochlorophenols by irradiation with visible light in aqueous alkaline solution in the presence of photosensitizers and oxygen is described. The reactions were carried out in the absence or presence of detergents. The photosensitizers used were Al(III), Zn(II) and Ga(III) complexes of 2,9,16,23-tetrasulphophthalocyanine (1a–1c), 5,10,15,20-tetrakis(4-carboxy-phenyl)porphyrin (2), a cationically charged perylene tetracarboxylic acid diimide (3), rose bengal (4) and methylene blue (5). The photosensitizers exhibit different activities and photo-oxidative stabilities which are strongly dependent on the pH, hydrolysis sensitivity and aggregation tendency. Singlet oxygen, obtained by photoinduced energy transfer from the excited photosensitizers, dominates the initial steps of photo-oxidation. A reaction sequence is proposed on the basis of the identification of carbon dioxide and maleic or fumaric acid as the products of photo-oxidation in the absence of detergent and the evaluated mass balances.

Phthalocyanines and Phthalocyanine Analogues: The Quest for Applicable Optical Properties

Summary. The central subject of this article is the description of the current work of the authors in the context of the Cost Action 518, project DE-1, and the Phthalocyanines Research Training Network, both financed by the European Community. The aim of the above projects is the design, synthesis, and structural and physical characterization of molecular and polymeric materials based on phthalocyanine derivatives with particular optical properties, as well as the study of their technological applications in the sensors field.

Efficient oxidations and photooxidations with molecular oxygen using metal phthalocyanines as catalysts and photocatalysts

Metal phthalocyanines can be very efficient as catalysts and photocatalysts in oxidation reactions using molecular oxygen as oxidant. Different types of soluble low molecular weight or oligomeric and insoluble heterogeneous catalysts and photocatalysts were developed. The heterogeneous metal phthalocyanines exist either impregnated on SiO2, Al2O3, charcoal and TiO2 or covalently and coordinatively bound on SiO2 and organic polymers or ionically bound on an organic ion exchanger. The catalytic oxidations of toxic sulfide and thiol derivative are studied. In addition, toxic phenols were employed as substrates for the photooxidation. Heterogeneous catalysts can exhibit higher activities then low molecular weight phthalocyanines. These systems exhibit a good stability for re-use. Photooxidations are more efficient than oxidations. A Si(IV) phthalocyanine derivative on a polymer ion exchanger is most active and stable. Also some examples for photooxidations in the direction of photochemical synthesis are given.

Un symmetrica My Substituted Benzonaphthoporphyrazines: A New Class of Cationic Photosensitizers for the Photodynamic Therapy of Cancer*

Abstract— Unsymmetrical zinc(II) complexes of benzonaphthoporphyrazines 5 a‐12a bearing between one and eight pyri‐dyloxy substituents are synthesized by statistical tetra‐merization of 6‐(l,l‐dimethylethyl)‐2,3‐naphthalenedi‐carbonitrile (1) with 4‐(3‐pyridyloxy)‐ or 4,5‐bis‐(3‐pyri‐dyloxy)‐1,2‐benzenedicarbonitrile (2, 3). Methylation of 5a‐12a leads to the cationic pyridyloxybenzonaphtho‐porphyrazines 5b‐ 12b having between one to eight positive charges. The Q‐band transition in the visible spectra exhibits a bathochromic shift from 680 to 760 nm dependent upon the number of annelated naphthalene rings. The singlet oxygen quantum yields of the benzonaphthoporphyrazines determined by the dye‐sensitized photoox‐idation of 1,3‐diphenylisobenzofurane is surprisingly high (in the range of zinc phthalocyanine). The photoox‐idative stabilities of the photosensitizers described quantitatively by first‐order kinetics decrease with the number of annelated naphtho groups. A linear correlation between the logarithm of the decomposition rate constant and the position of the highest occupied molecular orbital (HOMO)‐level of the photosensitizers is found. Destabi‐lization of the HOMO leads to a decrease of the pho‐tostability. Due to their adjustable long wavelength absorption, their intramolecular polarity axis and their different hydrophilic/hydrophobic character, these novel compounds may be suitable photosensitizers for the photodynamic therapy of cancer.

Synthesis of positively charged phthalocyanines and their activity in the photodynamic therapy of cancer cells

Abstract— Positively charged zinc containing or metal free phthalocyanines 6a‐c and 7a‐c were prepared via a three step procedure starting from 4‐nitrophthalonitrile. The phthalocyanines contain alkyl chains of different length in order to influence the hydrophilic vs lipophilic character of the compounds. The partition between a hydrophilic (water) and lipophilic (octanol‐1) phase was determined, and the photoredox activities were investigated. Initial results on the photodynamic activity of these compounds were compared with those of Doughertys Photofrin II on different malignant and non‐malignant cell lines (XP 29MAmal, CXI, HeLa, S180 and N017). Positively charged phthalocyanines in vitro showed a higher photodynamic activity than Photofrin II.

Synthesis of faujasite supported phthalocyanines of cobalt, nickel and copper

Abstract Faujasite supported phthalocyanines of cobalt, nickel and copper are prepared by the reaction of ion-exchanged zeolites with 1,2-dicyanobenzene. The fraction of encaged phthalocyanine decreases in the sequence CoPc-X > NiPc-X > CuPc-X, which is interpreted with a respective increase of the Bronsted acidity in the zeolite framework.