Günter Schnurpfeil

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 ...

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.

Efficient synthesis of phthalocyanines and related macrocyclic compounds in the presence of organic bases

Abstract Various unsubstituted and substituted aromatic 1,2-dinitriles were converted in the presence of strong bases such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5-diazabicyclo [4.3.0] non-5-ene (DBN) in bulk reactions or an n-pentanol in high yields to metal-free phthalocyanines and related macrocyclic compounds. These efficient pathways, using commercially available bases, are easy to perform and work under relatively mild conditions. Bases weaker than DBU or DBN result in lower yield of phthalocyanines or impure products. Reactions in the presence of metal salts lead to metal phthalocyanines in yields similar to the metal-free analogues.

Macromolecule-metal complexes

In macromolecule metal complexes (MMCS), suitable compounds are combined to give materials with new and unusual properties. MMCs are organic or inorganic high molecular weight compounds incorporating metal/ion complexes/chelates or metal clusters. In order to appreciate the range of properties shown by MMCs, one has only to look at the following functions of natural MMC systems: metalloenzymes for catalysis; hemoglobin, myoglobin for gas transport; cofactors for electron interaction; the means of photosynthesis for energy conversion; metalloproteins and related systems for various functions. Selective properties are realized by special molecular arrangements. These arrangements may involve the primary structure (composition of a MMC), the secondary structure (steric orientation of a MMC unit), the tertiary structure (orientation of the whole MMC), or a quaternary structure (the interaction of different MMCs). The more detailed knowledge of biological MMCs has led in recent years to intensified research activity in the field of synthetic MMCs. MMCs can be classified into three main groups.

Investigations of n/p-junction photovoltaic cells of perylenetetracarboxylic acid diimides and phthalocyanines

The preparation of organic photovoltaic cells in the configuration ITO/n-conductor/p-conductor/Au obtained by vapour deposition of the organic compounds is described in detail. As n-conductors perylenetetracarboxylic acid diimides (e.g., dimethyl derivative) and as p-conductors phthalocyanines (e.g., zinc phthalocyanine) were used. The film thicknesses of the layers were varied between 10 and 250 nm. The following investigations were carried out: reproducibility of cell preparation, influence of purity of the organic materials, the type of ITO substrate, deposition rate, substrate temperature and thickness of the organic films. Photovoltaic parameters were determined as follows: short-circuit currents ⩽ 3.5 mA cm–2, open-circuit voltages ⩽ 685 mV, fill-factors ⩽ 0.52, photovoltaic efficiencies < 0.43% under white light of 100 mW cm–2. The cells exhibit a high series resistance of around 70 Ω cm2 and a low shunt resistance of around 670 Ω cm2. Under 1 mW cm–2 illumination the efficiency increased to 1.6%. In a cell of ITO/n-conductor (10 nm)/p-conductor (50 nm)/Au quantum yields up to 80% were obtained. Results of stability measurements show a 50% decrease in the short-circuit current over time. The results are discussed in detail considering the positions of energy levels in the n- and p-conducting materials.

Photo‐oxidative Stability and its Correlation with Semi‐empirical MO Calculations of Various Tetraazaporphyrin Derivatives in Solution

The photo-oxidative stability of various annelated and substituted tetraazaporphyrin derivatives were investigated in N,N-dimethylformamide by irradiation in the presence of air. First-order rate constants were calculated. In addition, the positions of the HOMO and LUMO energy levels of the compounds were calculated using a commercially available program. A linear correlation between the experimental values of the rate constants and the theoretical values of the HOMO position exists. The method described allows one to predict the photo-oxidative stability by calculating their HOMO levels, which is very important for the use of macrocyclic metal complexes in photo-oxidation reactions in solution. From the calculated triplet energies it is considered that the macrocyclic metal complexes can convert by photoinduced energy transfer triplet oxygen to singlet oxygen. Experimentally, tetraazaporphyrin derivatives show high quantum yields of singlet oxygen formation under irradiation. No correlations of the quant...

Syntheses of uncharged, positively and negatively charged 3,4,9,10-perylene-bis(dicarboximides)

Abstract The preparation of various 3,4,9,10-perylene-bis(dicarboximides) bearing uncharged, negatively and positively charged substituents on the imide group is described. The absorption and fluorescence bands are not influenced by the type of substituent, but in contrast, the fluorescence quantum yields of the compounds are different.

Langmuir-Blodgett films of phthalocyanine derivatives: mono- and multilayer films prepared from phthalocyanine derivatives containing polar and cationic substituents☆

Abstract Uncharged tetraalkylamidophthalocyanines (1a-1d), tetracationic tetrapyridiniophthalocyanines (2a, 2b) and tetraammoniumphthalocyanine (3) are employed for the preparation of films by the Langmuir-Boldgett technique. Especially 1d, 2a and 2b bearing long-chain alkyl groups at the polar or cationic substituents gave stable monofilms, which were transferred to hydrophobized glass substrates. Interpretation of the visible transmission spectra of transferred monolayers taken in polarized light combined with the molecular areas in condensed monolayers (0.7–1.45 nm2) leads to the conclusion that in these “monofilms” the phthalocyanine rings are lying flat on the substrate surface, but these films consist of more than one single monolayer. This flat orientation is probably due to the combination of flexible hydrophobic alkyl moieties with hydrophilic polar or charged groups directly attached to the phthalocyanine ring.

An Optimal Design for Photovoltaic Properties of Two-Layer Organic Solar Cells Using Phthalocyanine and Perylene Derivatives

Abstract Photovoltaic properties of two-layer organic p/n junction solar cells were studied for vacuum-deposited films of p-type phthalocyanine derivatives having different π-electron conjugating macrocycles and n-type N,N′-substituted 3, 4:9, 10-perylenebis(dicarboximide) having different peripheral groups. The power conversion efficiency was optimized by controlling the film thickness, morphology and contact with top-electrodes. The film morphology of the perylene derivatives changed depending on their peripheral alkyl groups, and higher photocurrents were obtained for the cell with a homogeneous layer of perylene derivatives. The molecular modification in p-type phthalocyanine derivatives changed the cell photovaltage. A substitution with electron-withdrawing groups, which lowered the highest occupied molecular orbital (HOMO) energy of the p-type molecules, increased the photovoltage. On the other hand, an extention of the macrocyclic ring from phthalocyanine to naphthalocyanine lowered the photovoltai...