Journal of Porphyrins and Phthalocyanines

We report here, our experimental results and theoretical analysis of the dispersion data of nonlinear absorption in zinc meso-tetra-(p-methoxyphenyl)tetrabenzoporphyrin (ZnmpTBP). Using a ns optical parametric oscillator (OPO) we obtain the open aperture Z-scan data over the visible region starting from 480 nm to 600 nm. We use a more general five-level model for evaluating the excited state parameters like excited state absorption coefficients, two-photon absorption coefficient, etc. Due to its large excited state absorption cross-sections this material acts as a very good candidate for a broadband optical limiter in the visible region.

A number of octaphenoxyphthalocyaninato silicon complexes containing a variety of axial ligands, represented by (OPh)₈PcSi(X)₂ (where X = chloro3, hydroxy 4, (4-carboxybenzene) acetato 5, isonicatinato 6, propionato 7, nitrophenoxy 8 and dimethylaminoxy 9) have been synthesized using a convenient route starting with the 4,5-diphenoxy-1,2-dicyanobenzene. ¹H NMR and UV/vis spectra, and the cyclic voltammetry of the complexes are reported. The complexes are obtained in high yield and are soluble in many organic solvents. Cyclic voltammetry revealed two reduction couples and one oxidation couple for these complexes. Analysis of the cyclic voltammograms showed that compounds 6 and 8 were easier to oxidize and more difficult to reduce than the rest. Also cyclic voltammetry data suggested that electron transfer was not governed only by diffusion.

Reducing sugars and sodium hydroxide react with phthalonitrile and 4-methoxyphthalonitrile to form mixtures of the phthalocyanine and oligomers. The oligomers, obtained in yields up to 54%, were deduced to have a structure that is predominantly polyazine with the o-cyanophenyl group as a substituent from elemental analysis and spectral data. Since carbohydrate related compounds lacking the reducing linkage gave no products, it is suggested that the observed reactions require the α-hydroxycarbonyl grouping.

The preparation and luminescence properties of a dipalladium cofacial porphyrin dimer (DPA)Pd₂ (where DPA is the tetraanion of 1,8-bis(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrin-5-yl)anthracene) are reported and compared together with the photophysical behavior of the known monomeric (OEP)Pd and (TPP)Pd complexes. The effect of dioxygen in the presence and in the absence of the very bulky base, 1-t-butyl-5-phenylimidazole, is also investigated. The title dimer, (DPA)Pd₂, shows fluorescence and phosphorescence in the ps and ms time scale, respectively, with a global intensity lower than that of the porphyrin monomer analogues. The fluorescence sensitivity towards dioxygen quenching appears greater for the dipalladium complex than that of the monoporphyrin derivatives. In the presence of the bulky base, this sensitivity shows a dramatic decrease.

A ¹³C NMR spectral study of 29 arylporphyrin derivatives is presented. In all of the tetrasubstituted and trisubstituted compounds examined the α- and β-carbons exhibited the expected broadened signals. In complete contrast, the diphenylporphyrins all showed sharp α- and β-carbon peaks which facilitated structural confirmation. These observations have been correlated with differing tautomeric exchange rates.

The synthesis and characterization of a soluble metal-free polyethyleneoxide-capped phthalocyanine and the corresponding lead compound are described. This phthalocyanine was designed to allow the formation of dimers but to inhibit formation of higher aggregates. The monomer/dimer equilibrium constant in chloroform solutions is 750 ± 20 l mol^-1. No evidence for higher aggregates was found. The molecular extinction coefficient of the metal-free polyethyleneoxide-capped phthalocyanine in chloroform is one of the lowest known (2.5 × 104 l mol^-1cm^-1). The lead-substituted material was demonstrated to be a reverse saturable absorber from 532 nm to about 610 nm. It possesses a large nonlinear absorption coefficient in the visible and is a promising optical limiter material.

The competition of the radiation sensitizer motexafin gadolinium (Xcytrin^®, gadolinium(III) texaphyrin) and several other water-soluble metallotexaphyrin complexes with N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) for solvated electrons and hydroxyl radicals was studied using pulse radiolysis and by steady-state γ-radiolysis. It was found that the one-electron reduced forms (M-Tex^·+) of the Gd(III), Eu(III), Dy(III), Yb(III), and Cd(II) texaphyrin complexes, after an initial reaction with hydrated electrons, do not compete with TMPD for hydroxyl radicals formed under pulse radiolytic conditions. By contrast, the reduced Y(III), In(III), Tm(III), and Lu(III) texaphyrin complexes do. These differences in competitive reactivity toward ^.OH are rationalized in terms of the relative rates of protonation of the various singly reduced texaphyrins. In the case of Gd-Tex²⁺ in particular, the one-electron reduced product, Gd-Tex^·+, protonates rapidly, producing a redox-inactive species that does not react appreciably with ^.OH. By contrast, the one-electron reduced product from, e.g., Lu-Tex²⁺ (motexafin lutetium), does. These results may explain, at least in part, why the Gd(III) texaphyrin functions as a radiation sensitizer in vivo, while the analogous Lu(III) complex does not.

Four diads consisting of a free-base or zinc aryl-porphyrin associated with two ruthenium(II) bis(terdentate) complexes (non-cyclometallated Ru(N6) or cylometallated Ru(N5C)) have been synthesized. The strong electron-withdrawing properties of the Ru(N6) as compared to the Ru(N5C) complex have been illustrated by their electrochemical and spectroscopic properties. Emission spectra of the diads and the reference compounds have shown that very efficient fluorescence quenching occurs, probably by energy transfer processes from the porphyrin to the ³MLCT excited state of the ruthenium unit.