Journal of Porphyrins and Phthalocyanines

The synthesis of a series of novel tetra-(benzo-24-crown-8)-phthalocyanines (Mg(II), Ni(II) and Co(II)) as well as a modified procedure for the free-base ligand and its Zn(II) and Cu(II) complexes are reported. The tendency of these phthalocyanines to undergo supramolecular cofacial dimerization induced by interaction with a viologen ($N,N$-di(but-3-ynyl)-4,4$\prime$-bipyridinium) was investigated by UV-vis absorption and EPR spectral studies in solution. The nature of the metal cation in phthalocyanine, the concentration, as well as the solvent all influenced the assembly processes.

Three derivatives of chlorin e6 (1–3) were synthesized by introduction of maleimide, cysteine and glutathione at C-13 carboxyl of the chlorin scaffold. The evaluation of their PDT effects showed that compound 1, the derivative with a maleimide group, exhibited more potent photocytotoxicity against HepG2 cells (IC${}_{50}$ 3.2 $\mu$M) than 2 (IC${}_{50}$ 6.7 $\mu$M) and 3 (IC${}_{50}$ 10.2 $\mu$M), although the cellular uptake of 1 was slightly lower than that of 2 and 3. The high PDT effect of 1 was found to be in agreement with the high level of intracellular singlet oxygen. Further investigation of the mechanism revealed that 1 can significantly lower the GSH level in HepG2 cells due to the addiction reaction of maleimide and GSH, thus resulting in the reduction of ROS scavenging and the enhancement of cellular oxidative stress. This approach to improve PDT effects of photosensitizers by means of interfering with the cellular redox system and enhancing cellular oxidative stress offers a new strategy for development of photosensitizers in cancer therapy.

We report the dynamics of a intramolecular photoinduced electron transfer reaction of Zn(II)-porphyrin dyads that have a 2,2$\prime$-bipyridine moiety at the periphery in the presence of Cu${}^{2+}$ in methanol studied using laser flash photolysis with a sub-nanosecond time resolution. The photoinduced electron transfer reactions were observed from the excited $S_1$ and $T_1$ states of the Zn(II)-porphyrin to the Cu(II)-2,2$\prime$-bipyridine moiety, and the structural dependence of the reactivity were discussed in terms of the distance between the electron donating and accepting centers.

We have prepared a new $\mu$-oxo iron(III) porphyrin complex based on the simplest possible porphyrin ligand, porphine. Our structure determination for {[Fe(porphine)]₂O}shows that it has a decidedly different molecular structure compared to all other $\mu$-oxo iron(III)porphyrin complexes with two independent porphyrin ligands. The Fe–O–Fe angle is 153.21 (16)${}^{\circ }$which leads to a small interplanar angle of 22.7${}^{\circ }$between the two porphine rings. This also leads to C${}^{\dots }$C nonbonded contact as short as 3.35Å between the two rings. The twist angle of the two porphine rings is 16.8${}^{\circ }$. Other structural features are in general accord with those expected for high-spin iron(III) porphyrinates.

An amphiphilic zinc porphyrin complex with a typical donor–acceptor (D–A) structure was synthesized, where the triphenylamine acted as a donor unit while the porphyrin was used as an electronic acceptor. Due to the presence of triethylene glycol moieties on the parent structure, Zn-TPAP could spontaneously assemble to the related nanoparticles (Zn-TPAP NPs) with improved hydrophilicity. The as-prepared Zn-TPAP NPs presented relatively uniform spherical particles with the average particle sizes around 160 nm, which was suitable for tumor accumulation benefiting from the EPR effect. Due to the aggregation of the porphyrin molecules in the assembled nanostructures, Zn-TPAP NPs displayed broadened and red-shifted absorption and quenched fluorescence relative to that of Zn-TPAP. In addition to ROS generation, Zn-TPAP NPs exhibited moderate photothermal effects and the photothermal conversion efficiency was measured as 29%. Zn-TPAP NPs showed good biocompatibility and could generate ROS in the A549 cells. Under light irradiation, Zn-TPAP NPs can efficiently kill cancer cells. Thus, Zn-TPAP NPs could be used as potential nanoagents for cancer treatment through the photothermal/photodynamic synergistic modes.

A simple meso-pyrrolyl BODIPY-Schiff base conjugate was synthesized by reacting ($\alpha$-formylpyrrolyl) BODIPY with 2-aminophenol in ethanol at reflux followed by recrystallization from CH₂Cl₂/petroleum ether, affording the conjugate in 72% yield. The conjugate was thoroughly characterized by HR-MS, 1D and 2D NMR and X-ray crystallographic techniques. The X-ray structure of the meso-pyrrolyl BODIPY-Schiff base conjugate revealed that the meso-pyrrole and the phenyl substituents were deviated by an angle of $35^{\circ }$ and $49^{\circ }$, respectively, from the plane of the BF₂-dipyrrin core. The absorption spectrum of the conjugate was similar to the ($\alpha$-formylpyrrolyl) BODIPY with a strong absorption band at 508 nm, whereas the fluorescence of the ($\alpha$-formylpyrrolyl) BODIPY was completely quenched in the BODIPY-Schiff base conjugate. Furthermore, cation sensing studies revealed that the conjugate has a specific sensing ability for the Cu(II) ion even in the presence of the other metal ions, as verified by the visual, absorption and mass spectral studies. The DFT optimized structure revealed that the Cu(II) ion was bound to pyrrolic nitrogen, imine nitrogen, phenolic oxygen and two water molecules in a distorted square pyramidal fashion. TD-DFT studies accounted well for the absorption spectra of the BODIPY-Schiff base conjugate and its Cu${}^{2+}$ bound complex.

The optical limiting properties of three meso-pentafluorophenylstyrylBODIPY dyes are investigated in the presence and absence of methyl groups at the 1,7-positions that hinder free rotation of the meso-aryl group. Pentafluorophenyl groups are introduced at the meso-position, while 4-diethylaminostyryl groups are introduced at the 3- and/or 5-positions to form dyes with strong donor-$\pi$-acceptor (D-$\pi$-A) properties to enhance the dipole moment of the molecule. Favorable optical limiting properties are obtained for all three dyes, with the highest second-order hyperpolarizability value obtained for a monostyryl dye with no methyl groups at the 1,7-position. Bromination at the 2,6-positions of a 1,7-methyl substituted dye is found to result in second-order hyperpolarizability that is an order of magnitude lower than that calculated for the analogous non-halogenated dye.

Tin(IV) complexes of a 4-methylthiophenyl functionalized porphyrin (1-Sn) and its corrole analogue (2-Sn) were synthesized so that their photophysicochemical properties and photodynamic activities against MCF-7 breast cancer cells could be compared. Singlet oxygen luminescence studies revealed that 1-Sn and 2-Sn have comparable ${\mathrm{\Phi }}_{\mathrm{\Delta }}$ values in DMF of 0.59 and 0.60, respectively, while the IC${}_{50}$ values after irradiation of MCF-7 cells for 30 min with a Thorlabs 625 nm LED (432 J · cm${}^{-2})$ were determined to be 12.4 and 8.9 $\mu$M. The results demonstrate that the cellular uptake of 2-Sn and its molar absorptivity at the irradiation wavelength play a crucial role during in vitro cytotoxicity studies.

The geometrical and electronic structures of iron and cobalt metal complexes of porphyrazine and tetra(1,2,5-thiadiazole)porphyrazine in ground and low-lying excited electronic states were determined by DFT calculations and the complete active space (CASSCF) method with following accounting dynamic correlation by multiconfigurational quasidegenerate second-order perturbation theory (MCQDPT2). A geometrical structure of D${}_{4h}$ symmetry has been obtained for all four complexes. According to data obtained by the MCQDPT2 method, the complexes of cobalt and iron possess the ground states ²A${}_{1g}$ and ³A${}_{2g}$, respectively, and wave functions of the ground states have the form of a single determinant. It is shown that the crystal field theory (CFT) can be used to describe the sequence of electronic states of the investigated complexes. The nature of the bonds between metal atoms and nitrogen atoms has been described using the analysis of the electron density distribution in the frame of Bader’s quantum theory of atoms in molecule (QTAIM).