Eva H. Mørkved

Azaphthalocyanines with extended conjugation through heteroaryl and aryl substituents: Photochemical and photophysical properties

Magnesium and zinc complexes of azaphthalocyanines (AzaPc) with eight peripheral aromatic (phenyl) or heteroaromatic (pyridyl, thienyl, furyl) substituents are studied from the point of view of their singlet oxygen (ΦΔ) and fluorescence (ΦF) quantum yields, and UV-vis absorption spectra. Zn complexes have higher ΦΔ than Mg complexes by a factor of two, whereas the Mg complexes have higher ΦF than Zn complexes, also by a factor of two. Thienyl AzaPc have the highest ΦΔ among all studied substances (0.635 for Zn complex) followed by phenyl and pyridyl derivatives. The order of ΦF values is then reversed - the highest values were reached for pyridyl and phenyl derivatives followed by thienyl AzaPc. Both furyl AzaPc were unstable towards light and decomposed giving very low ΦΔ and ΦF. The Q-bands of the furyl and thienyl AzaPc were red-shifted for approx. 20 nm compared to phenyl and pyridyl derivatives indicating lower sterical hindrance between five-membered rings and thus allowing better conjugation of π-systems. Pyridyl-, thienyl- and furyl-substituted pyrazino[2,3-b]pyrazine-2,3-dicarbonitriles were also prepared but decomposed during attempted cyclotetramerizations.

Syntheses of Octa(2-heteroaryl) Azaphthalocyanines

Magnesium, copper(II) and nickel(II) complexes of octasubstituted azaphthalocyanines 3 — 5 have been prepared from di-fur-2-yl, di-thien-2-yl and di-pyrid-2-yl pyrazine-2,3-dicarbonitriles 2. Compounds 2 were prepared in good yields from condensations of diaminomaleonitrile and the diketones 2,2′-furil, 2,2′-thenil and 2,2′-pyridil. AzaPcs 3—5 give green pyridine solutions with Q-bands at 650—670 nm and e-values of 60 000—190 000.

Influence of protonation of peripheral substituents on photophysical and photochemical properties of tetrapyrazinoporphyrazines

Octasubstituted zinc tetrapyrazinoporphyrazines with four N,N-dimethylaminophenyls and four phenyl or pyridin-3-yl substituents were synthesized and fully characterized. Their fluorescence quantum yields in DMF or pyridine were very low, almost undetectable, as a consequence of ultrafast intramolecular charge transfer. Titration of their DMF solutions with sulfuric acid led to increase of the fluorescence quantum yields by two orders of magnitude when the full protonation of peripheral substituents was achieved. Intramolecular charge transfer is no longer a favorable way of excited-state relaxation at full protonation of N,N-dimethylaminophenyl substituents because of loss of donor centers (free electron pair on its nitrogen). Similarly, singlet oxygen quantum yields also increased by two orders of magnitude when sulfuric acid was added to tetrapyrazinoporphyrazine solutions in DMF. Protonation at azomethine nitrogens of tetrapyrazinoporphyrazine macrocycle was observed at higher acid concentrations and it led to considerable decrease of fluorescence quantum yields. Octaphenyl zinc tetrapyrazinoporphyrazine and octa(pyridin-3-yl) zinc tetrapyrazinoporphyrazine were used as controls without intramolecular charge transfer. Their fluorescence and singlet oxygen quantum yields were high in DMF and decreased at higher concentrations of sulfuric acid due to protonation of azomethine nitrogens. The results suggest that the photophysical and photochemical properties of studied compounds may be controlled by changes of pH of medium.

Syntheses of octa(dialkylamino)azaphthalocyanines

Nickel(II) octa(4-morpholinyl)- (11a) and copper(II) octa(1-pyrrolidinyl)- (11b) azaphthalocyanines have been prepared from the corresponding pyrazine diiminoimides (10). The precursor pyrazine dicarbonitriles (2) gave 6-cyanopyrazine-5-alkyl carboximidates (3-9) as stable intermediates when reacted with ammonia and catalytic amounts of sodium alkoxide in alcohols. Compounds 3-9 were converted to the diiminoimides 10 upon reflux in propanol or butanol for several hours. This unusual reaction pattern was observed for pyrazine-2,3-dicarbonitriles 2 substituted in the 5- and 6-positions with morpholine, thiomorpholine, piperidine or pyrrolidine.

Zn(quinoline)2Cl2: an efficient reagent for synthesis of zinc azaphthalocyanines with thiomorpholine- or pyrazole substituents

The Zn(quinoline)2Cl2 complex is found to be a convenient reagent for the direct synthesis of amino-substituted, zinc azaphthalocyanines. Octa(4-thiomorpholinyl)- and octa(1-pyrazolyl)- substituted zinc azaphthalocyanines were synthesized from pyrazines, 5,6-bis(4-thiomorpholinyl)pyrazine-2,3-dicarbonitrile and 5,6-bis(1-pyrazolyl)pyrazine-2,3-dicarbonitrile, respectively and dry Zn(quinoline)2Cl2. Two zinc azaphthalocyanines, both mixtures of four constitutional isomers, were synthesized by the same method, from 6-(2-thienyl)-5-(4-thiomorpholinyl)pyrazine-2,3-dicarbonitrile and from 6-(2-thienyl)-5-(1-pyrazolyl)pyrazine-2,3-dicarbonitrile respectively. The octa(4-thiomorpholinyl)- and octa(1-pyrazolyl)-substituted zinc azaphthalocyanines and the zinc azaphthalocyanines with mixed substituents were characterized by elemental analyses, TOF-SIMS, 1H and 13C NMR, and UV-vis spectroscopic methods. Q-bands for octa(4-thiomorpholinyl)- and octa(1-pyrazolyl)-substituted zinc azaphthalocyanines and the zinc azaph...

Synthesis and properties of novel components for organic metals : dihydrotellurophene derivatives

Two series of dihydrotellurophenes have been synthesized: derivatives of 4,6-dihydro-1H,3,H-telluropheno[3,4-c ]tellurophene (1) and derivatives of 1,3,6,8-tetrahydrobenzo[1,2-c;3,4-c′]ditellurophene (2). X-Ray structure determinations confirm the tetraiodo structures of 1a and 2a. The tetraiodo derivatives are reduced by sodium borohydride to the corresponding dihydrotellurophenes, 1b and 2b, which undergo the characteristic divalent tellurium reaction with iodomethane to form telluronium methiodides. Both dihydrotellurophenes 1b and 2b are moderate electron donors and react with 7,7,8,8-tetracyanoqiunodimethane TCNQ affording blue semiconductive solids.

Matrix-assisted laser desorption/ionization and Fourier transform ion cyclotron resonance mass spectrometry of metalloporphyrazines and metallophthalocyanines

High-resolution matrix-assisted laser desorption/ionization (MALDI) mass spectra of the title compounds were obtained using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The results show that this technique is well suited for obtaining molecule ions of the title compounds. The main peaks in the spectra are due to the molecular ion, M+• and/or the protonated molecule, MH+. Little fragmentation is observed. Isotopic masses were measured for one of the compounds with an estimated accuracy of ± 5 ppm. In addition, experiments were performed with the neat compounds, without a matrix. This direct laser desorption method is useful in some cases, but is generally not applicable for these types of compounds, even when great care is exercised in controlling the laser pulse energy.

Resonance in aromatic and heteroaromatico-dicarboxylic acids, their anhydrides and imides

It is found thato-dicarboxylic acids derived from pyrrole and 1,2,5-thiadiazole do not form cyclic anhydrides as readily as phthalic acid. This is discussed in terms of ionic resonance structures and derived stabilization of the anhydrides and acids.

o-Quinonoid heterocycles: synthesis and crystal structure of 2,3-dicyano-5,7-bismethylthieno[3,4-b]pyrazine.

2,3-Dicyano-5,7-bismethylthieno[3,4-b]pyrazine (5), has been obtained as a minor product from reactions of S-nucleophiles with 5,6-di(1-bromoethyl)pyrazine-2,3-dicarbonitrile (3), or from a condensation of 4-hydroxy-2,5-dimethyl-2,3-dihydrothiophen-3-one (4) with diaminomaleonitrile. The molecular structure of compound 5 has been confirmed by X-ray diffraction. A partial separation of charge causes a donor-acceptor type arrangement of the planar molecules in uniform parallel stacks with an interplanar spacing of 3.334(2) A at 100 K.

Structure ofN, N′-diphenyl-N-(2-pyridmyl)urea hemihydrate: A crystallographic and spectroscopic investigation

N,N′-diphenyl-N-(2-pyridinyl)urea hemihydrate (C18H15N3O·1/2H2O) has been studied by crystallographic and NMR-spectroscopic methods. The crystals are monoclinic,I2/a with unit-cell parameters at 86K,a=17.820(1),b=14.857(1),c=11.299(1) Å,β=99.17(1)° andZ=8. The structure was solved by direct methods which involved the use of seventeenmeasured triplet phases in the starting set. This appears to be the first centrosymmetric structure solution being based extensively on physically acquired X-ray phases. Refinement was by full-matrix least-squares involving 3843Fo and yieldedR∼Rw=0.042. The shape of the molecules can be described approximately by two, nearly orthogonal planes, one containing pyridine, the urea group and the NH-bonded phenyl ring, the other containing the second phenyl ring. Both the X-ray and the NMR studies show that there is an intramolecular H-bond between the urea N and the pyridine N atoms. When pH is lowered, this H-bond is weakened, and eventually breaks due to protonation of the pyridine ring. The X-ray study indicates that about 20% of the pyridine rings in the crystal are protonated. The structure details of the rings, in particular the valency angles, have been analyzed in relation to the orientation of the rings relative to the main molecular plane, and the electronic effects of the substituants.