Oligomeric cadmium-phthalocyanine complexes: novel supramolecular free radical structures

Certain cadmium-metallated phthalocyanines give rise to EPR active triple-decker sandwich complexes containing two Cd ions and three phthalocyanine (Pc) ligands. These have been shown to form when the ligands bear either eight non- peripheral alkyl or alkenyl substituents or eight peripheral 2-ethylhexyl groups. They can be derived either from three equivalents of a cadmium phthalocyanine precursor or from a 2:1 mixture of a cadmium phthalocyanine (CdPc) and a metal-free phthalocyanine (H(2)Pc). The mode of their formation has been investigated by a series of "cross" experiments. The results indicate that the triple-decker structures are formed by a self-assembly process. This is deduced from results that show that they can disassemble and reassemble with incorporation of differently substituted ligands derived from either an H(2)Pc or CdPc. The reassembled structures in these cross experiments can contain more than one ligand that originated from either the added CdPc or, and more surprisingly, the H(2)Pc compound. Mass spectrometry has also established that higher order oligomers can be formed when steric requirements between the alkyl substituents on adjacent rings in the stack are reduced. Thus an isotopic cluster for a Cd(5)Pc(6) complex has been observed when the eight peripheral substituents are hexyl chains and tetrameric complexes are formed when two different ligands are incorporated within a stack, with one carrying substituents at the peripheral sites and the other bearing substituents at the non-peripheral sites.     

First example of a di-cadmium tris-phthalocyanine triple-decker sandwich complex

An unprecedented M(II)2Pc3 (M = Cd) triple-decker sandwich complex has been synthesized and characterised by single crystal X-ray crystallography; cyclic voltammetry shows an unusually large range of redox states and EPR spectroscopy indicates that the material exists in at least two redox states, one having spin (1/2).     

Measurement of the hyperfine splitting of the 1s state in muonic 7Li as a search for axial-vector muon-nucleon interactions

The magnetic hyperfine splitting (h.f.s.) in the 1s state of ⁷Li has been measured with a precision of 1% using the bent-crystal spectrometer facility at the SIN muon channel. With an instrumental resolution of 2.5 eV FWHM the h.f.s. was completely resolved in the 2p-1s transition. The result is ΔE(M1) = 4684 ± 49meV. A comparison of this result with the electromagnetic value yields a new upper limit for the strength of a possible muon-nucleon interaction mediated by an axial-vector boson, which is much lower than those that can be derived from other present data.     

Precision measurement of the wavelengths and natural line widths of 3d-2p pionic X-ray transitions in low-Z atoms

The wavelengths and the natural line widths of the 3d-2p transitions in the pionic atoms of ¹²C, ¹⁶O, ¹⁸O, ²⁴Mg, ²⁶Mg, ²⁸Si and ³⁰Si have been measured at SIN with a bent-crystal spectrometer. The precision reached in the transition wavelengths ranges from 4 to 18 ppm, and in the widths from 2 to 14%.     

Mesure de l'electroreflectance des metaux au moyen de structures metal-isolant-metal (Ag-Al2O3-Au)

Modulation of the voltage applied to a metal-insulator-metal structure induces a modulation of the reflectance, which has been measured with a lock-in amplifier. The spectrum of electroreflectance contains structures which are characteristic of both Ag-Al₂O₃ and Au-Al₂O₃ interfaces.     

Phthalocyanine analogues: unexpectedly facile access to non-peripherally substituted octaalkyl tetrabenzotriazaporphyrins, tetrabenzodiazaporphyrins, tetrabenzomonoazaporphyrins and tetrabenzoporphyrins

Controlled syntheses of phthalocyanine/benzoporphyrin hybrid structures have been achieved. We report a simple means for obtaining non-peripherally octaalkyl-substituted derivatives of tetrabenzotriazaporphyrin (TBTAP), tetrabenzodiazaporphyrin (TBDAP), tetrabenzomonoazaporphyrin (TBMAP) and tetrabenzoporphyrin (TBP) macrocycles by treating 3,6-dialkyl phthalonitriles with differing amounts of the Grignard reagent MeMgBr. This range of macrocyclic products is not obtained from corresponding reactions of a Grignard reagent with 4-substituted phthalonitriles, reported previously, or reaction of MeMgBr with a 4,5-dialkyl phthalonitrile. Attempts to form a meso-substituted TBTAP from 3,6-dialkyl phthalonitriles by reaction with benzyl and long-chain alkyl Grignard reagents unexpectedly gave only the parent macrocycle unsubstituted at the meso position. The synthetic protocols are by far the most straightforward and convenient means to access these interesting, but scarcely studied, classes of material. The new series of substituted macrocyclic compounds, obtained as the metal-free and magnesium- and copper(II)-metallated derivatives, show trends in the UV/Vis spectra consistent with those predicted elsewhere by Kobayashi. Characterisation of the new families allows further trends to be identified as meso-nitrogen atoms are sequentially replaced by methine bridges, for example, the compounds provide novel examples of macrocyclic structures that show columnar mesophase behaviour. Single-crystal X-ray structure determinations have been obtained for three magnesium-metallated derivatives bearing eight hexyl substituents and constitute the first set of structural data obtained for such a series.     

OCTA-ALKYL ZINC PHTHALOCYANINES: POTENTIAL PHOTOSENSITIZERS FOR USE IN THE PHOTODYNAMIC THERAPY OF CANCER

The synthesis, characterization and electronic spectra of a series of nine 1,4,8,11,15,18,22,25-octa-alkyl zinc phthalocyanines (ZnPc), potential photosensitizers for the photodynamic therapy of cancer, are described. The substituents on the phthalocyanine (Pc) macrocycle “red-shift” the absorbance maximum, in cyclohexane, of all nine members of this series to a value of 703 ± 2 nm, with a corrected fluorescence emission maximum for the octadecyl derivative of 715 nm. The solubilities and degree of aggregation of six examples in cyclohexane have been measured. The highest homologue, the octadecyl derivative, remains essentially unaggregated to a concentration of 1.5 ± 10^?4 mol dm^?3. The photostability of this Pc has been examined and the compound shown to be sensitive to photooxidation processes, which lead to its decomposition to 3,6-fcw-decylphthalimide. Known singlet oxygen quenchers inhibit the photodecomposition. In a comparative study, the octadecyl ZnPc underwent a more rapid photodecomposition than the corresponding metal-free derivative.