Photophysicochemical and fluorescence quenching studies of tetra- and octa-carboxy substituted silicon and germanium phthalocyanines

Abstract Spectral, photophysical and photochemical properties of tetra- and octa-carboxy substituted metallophthalocyanines containing silicon and germanium as central metals ((OH) 2 GeTCPc, (OH) 2 SiTCPc, (OH) 2 GeOCPc and (OH) 2 SiOCPc) have been studied in dimethylsulfoxide (DMSO) and the trends in triplet, fluorescence, singlet oxygen quantum yields and triplet lifetimes are described for these compounds. The GePc derivatives exhibited high triplet quantum yields ( Φ T  = 0.79 for (OH) 2 GeOCPc and 0.82 for (OH) 2 GeTCPc compared to Φ T  = 0.66 for (OH) 2 SiTCPc and 0.48 for (OH) 2 SiOCPc) due to the spin–orbit coupling induced by Ge(IV). The triplet lifetimes were higher for MOCPc ( τ T  = 760 μs for (OH) 2 SiOCPc and 480 μs for (OH) 2 GeOCPc compared to τ T  = 210 μs for (OH) 2 SiTCPc and 260 μs for (OH) 2 GeTCPc). The fluorescent states of the metallophthalocyanine (MPc) complexes were effectively quenched by benzoquinone (BQ) and the quenching course was found to follow a diffusion-controlled (dynamic) bimolecular mechanism. Theoretical values of bimolecular rate constant for the interaction of the complexes with BQ were determined using the Stokes–Einstein–Smoluchowski model, and values together with the Stern–Volmer quenching constants were used in calculating the fluorescence lifetimes of the complexes.

[1]  K. Morishige,et al.  Adsorption of CO, O2, NO2, and NH3 by Metallophthalocyanine Monolayers Supported on Graphite , 1997 .

[2]  T. Nyokong,et al.  Comparative photocatalytic efficiency of oxotitanium(IV) phthalocyanines for the oxidation of 1-hexene , 2007 .

[3]  G. Bock,et al.  Photosensitizing compounds : their chemistry, biology and clinical use , 1989 .

[4]  Yanhui Zhang,et al.  Highly Efficient, Mild, Bromide-Free and Acetic Acid-Free Dioxygen Oxidation of p-Nitrotoluene to p-Nitrobenzoic Acid with Metal Phthalocyanine Catalysts , 2005 .

[5]  N. Periasamy,et al.  Electron-transfer distance in intermolecular diffusion-limited reactions , 1991 .

[6]  Suzanne Fery-Forgues,et al.  ARE FLUORESCENCE QUANTUM YIELDS SO TRICKY TO MEASURE? A DEMONSTRATION USING FAMILIAR STATIONERY PRODUCTS , 1999 .

[7]  T. Nyokong,et al.  Excited state dynamics of zinc and aluminum phthalocyanine carboxylates. , 2007, Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy.

[8]  K. Sakamoto,et al.  Synthesis and electron transfer property of phthalocyanine derivatives , 1997 .

[9]  T. Nyokong,et al.  Photophysical and photochemical studies of sulphonated non-transition metal phthalocyanines in aqueous and non-aqueous media , 2005 .

[10]  T. Nyokong,et al.  Synthesis, photophysical and photochemical properties of aryloxy tetra-substituted gallium and indium phthalocyanine derivatives , 2007 .

[11]  L. Dicelio,et al.  Modeling of fluorescence quantum yields of supported dyes Aluminium carboxyphthalocyanine on cellulose , 1998 .

[12]  T. Nyokong,et al.  Photophysicochemical and fluorescence quenching studies of benzyloxyphenoxy-substituted zinc phthalocyanines. , 2008, Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy.

[13]  A. Harriman,et al.  Metal phthalocyanines and porphyrins as photosensitizers for reduction of water to hydrogen , 1982 .

[14]  D. Wöhrle,et al.  Photo-oxidative Stability and its Correlation with Semi-empirical MO Calculations of Various Tetraazaporphyrin Derivatives in Solution , 1997 .

[15]  A. Lever,et al.  Phthalocyanines : properties and applications , 1989 .

[16]  S. Gaspard,et al.  Singlet−singlet and triplet−triplet intramolecular transfer processes in a covalently linked porphyrin−phthalocyanine heterodimer , 1989 .

[17]  V. Ahsen,et al.  Synthesis, photophysical and photochemical properties of substituted zinc phthalocyanines. , 2007, Dalton transactions.

[18]  M. Stillman,et al.  Optical absorption and magnetic circular dichroism studies of hydrogen, copper(II), zinc(II), nickel(II), and cobalt(II) crown ether-substituted monomeric and dimeric phthalocyanines , 1989 .

[19]  R. Langlois,et al.  BIOLOGICAL ACTIVITIES OF PHTHALOCYANINES—VI. PHOTOOXIDATION OF L‐TRYPTOPHAN BY SELECTIVELY SULFONATED GALLIUM PHTHALOCYANINES: SINGLET OXYGEN YIELDS AND EFFECT OF AGGREGATION , 1987, Photochemistry and photobiology.

[20]  M. Hanack,et al.  Separation of 2(3),9(10),16(17),23(24)-Tetrasubstituted Phthalocyanines with Newly Developed HPLC Phases , 1996 .

[21]  N. Brasseur,et al.  Efficacy and mechanism of aluminium phthalocyanine and its sulphonated derivatives mediated photodynamic therapy on murine tumours. , 1997, European journal of cancer.

[22]  David Phillips,et al.  Excited singlet and triplet state electron-transfer reactions of aluminium(III) sulphonated phthalocyanine , 1982 .

[23]  L. Dicelio,et al.  Visible and near-IR spectroscopic and photochemical characterization of substituted metallophthalocyanines , 1993 .

[24]  T. Nyokong,et al.  Effects of central metal on the photophysical and photochemical properties of non-transition metal sulfophthalocyanine , 2005 .

[25]  J. Lakowicz.  Principles of fluorescence spectroscopy , 1983 .

[26]  Rudolph A. Marcus,et al.  On the Theory of Oxidation‐Reduction Reactions Involving Electron Transfer. I , 1956 .

[27]  Thomas J. Dougherty,et al.  Basic principles of photodynamic therapy , 2001 .

[28]  Steven L. Murov,et al.  Handbook of photochemistry , 1973 .

[29]  David Kessel,et al.  Photodynamic therapy of neoplastic disease , 1990 .

[30]  T. Nyokong,et al.  Photosensitizing properties of octacarboxy metallophthalocyanines in aqueous medium and their interaction with bovine serum albumin , 2008 .

[31]  Lelia E. Dicelio,et al.  Quantum yield of singlet molecular oxygen sensitization by copper(II) tetracarboxyphthalocy anine , 1989 .

[32]  Tebello Nyokong,et al.  Effects of substituents on the photochemical and photophysical properties of main group metal phthalocyanines , 2007 .

[33]  J. V. van Lier,et al.  Metal complexes as photo- and radiosensitizers. , 1999, Chemical reviews.

[34]  T. Nyokong,et al.  Photophysical and photochemical studies of zinc(II) phthalocyanine derivatives—effects of substituents and solvents , 2004 .

[35]  T. Nyokong,et al.  Synthesis, photophysical and photochemical studies of germanium and tin phthalocyanine complexes , 2002 .