Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 16. A rare class of uncharged water soluble complexes: UV-vis spectral, redox, and photochemical properties

The synthesis and physicochemical characterization of a new class of water soluble homo/heteropentanuclear porphyrazine complexes are described. The investigated compounds, prepared from the previously reported mononuclear species [ LM ]⋅x H 2 O (L = tetrakis-2,3-[5,6-di(2-pyridyl) pyrazino]porphyrazinato dianion; M = MgII ( H 2 O ), ZnII , CuII , CoII , PdII , PtII ; x = 3–8) in DMSO under mild experimental conditions, are represented as [{ Pd ( OAc )2}4 LM ]⋅x H 2 O (x = 11–22) and bear four Pd ( OAc )2 units, each externally coordinated at the vicinal pyridine N atoms of a single dipyridinopyrazine fragment of the porphyrazine macrocycle (py–py coordination). The newly synthesized compounds were examined by IR and magnetic susceptibility measurements in the solid state. Solution UV-visible spectral studies on all of the species were conducted in the low-donor organic solvents pyridine, dimethyl sulfoxide and dimethylformamide and in the water medium, whereas electrochemical measurements were performed in these media in the presence of tetrabutylammonium perchlorate (organic solvents) and KCl or NaOAc (water). Data on the photosensitizing activity for the generation of singlet oxygen, 1 O 2, of interest in photodynamic therapy, were also obtained in dimethylformammide solution on the compounds [{ Pd ( OAc )2}4 LM ]( M = MgII ( H 2 O ), ZnII , PdII , PtII ) and the measured ΦΔ values are presented and discussed. NMR spectral data on the complex [{ Pd ( OAc )2}4 LZn ] are also included and discussed.

Zinc(II) complexes of tetrakis-(6,7-quinoxalino)porphyrazine bearing externally appended 2-pyridyl rings: Synthesis, UV-visible spectral behavior and photoactivity for singlet oxygen generation

The synthesis and physicochemical properties of the Zn II complexes, [ Py 8 QxPzZn ]( Py 8 QxPz = tetra -2,3-[6,7-di(2-pyridyl)quinoxalino]porphyrazinato dianion), the corresponding octacation [(2- Mepy )8 QxPzZn ]8+ (neutralized by I - ions), and the heteropentanuclear complex [( PdCl 2)4 Py 8 QxPzZn ] are presented and discussed. According to their UV-visible spectral data in non aqueous solvents ( CHCl 3, pyridine, dimethyl sulfoxide, dimethylformamide), the species exhibit intense absorptions in the Q-band region at 750–770 nm, in line with parallel spectral data observed for the free base [ Py 8 QxPzH 2], also reported, and the previously investigated Mg II complex [ Py 8 QxPzMg ( H 2 O )]. The observed Q-band position for this series of "quinoxalinoporphyrazine" macrocycles is about 100 nm to the red with respect to the position of the same absorption for the series of the already reported "pyrazinoporphyrazine" analogs. The spectral effects induced by the peripherally appended methyl-pyridinium groups in the octacation [(2- Mepy )8 QxPzZn ]8+ or by exocyclic coordination in the complex [( PdCl 2)4 Py 8 QxPzZn ] are also considered. Of the investigated Zn II complexes, [ Py 8 QxPzZn ] and the related octacation [(2- Mepy )8 QxPzZn ]8+ are active in dimethylformamide solution as singlet oxygen photosensitizers, which is of interest for applications in the photodynamic therapy (PDT) of cancer.