Five-coordinate complex formation and luminescence quenching study of copper(II) porphyrins

Light-Emitting Porphyrin Derivative Obtained from a Subproduct of the Cashew Nut Shell Liquid: A Promising Material for OLED Applications

In this work, the meso-tetra[4-(2-(3-n-pentadecylphenoxy)ethoxy]phenylporphyrin (H₂P), obtained from the cashew nut shell liquid (CNSL), and its zinc (ZnP) and copper (CuP) metallic complexes, were applied as emitting layers in organic light emitting diodes (OLEDs). These compounds were characterized via optical and electrochemical analysis and the electroluminescent properties of the device have been studied. We performed a cyclic voltammetry analysis to determine the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energy levels for the porphyrins, in order to select the proper materials to assemble the device. H₂P and ZnP presented fluorescence emission band in the red region, from 601 nm to 718 nm. Moreover, we verified that the introduction of bulky substituents hinders the π–π stacking, favoring the emission in the film. In addition, the strongest emitter, ZnP, presented a threshold voltage of 4 V and the maximum irradiance of 10 μW cm⁻² with a current density (J) of 15 mA cm⁻² at 10 V. The CuP complex showed to be a favorable material for the design of OLEDs in the infrared. These results suggest that the porphyrins derived from a renewable source, such as CNSL, is a promising material to be used in organic optoelectronic devices such as OLEDs.

Nanorings with copper(ii) and zinc(ii) centers: forcing copper porphyrins to bind axial ligands in heterometallated oligomers

The affinity of copper(ii) porphyrins for pyridine ligands is extremely weak, but oligo-pyridine templates can be used to direct the synthesis of Cu-containing cyclic porphyrin oligomers when they also have Zn centers. We report the synthesis of two heterometallated nanorings: a six-porphyrin ring prepared from a Zn/Cu/Zn linear trimer and a ten-porphyrin ring prepared from a Zn/Zn/Cu/Zn/Zn pentamer. Both these macrocycles have copper porphyrins at two specific positions across the diameter of the ring and zinc at other sites. The presence of a paramagnetic metal results in broadening of the 1H NMR spectra and reduces the relaxation time constants (T1 and T2). The changes in T1 provide quantitative information on the distance of each proton from the copper atom. The Zn/Zn/Cu/Zn/Zn linear porphyrin pentamer binds strongly to a penta-pyridyl template, despite the weakness of the Cu-N interaction, because of the chelate cooperativity of the neighboring Zn-N coordination. The stabilities of a family of four linear porphyrin pentamer complexes were determined by UV-vis-NIR titration and analyzed using a chemical double-mutant cycle. The results show that the free energy of interaction of a copper center to axial pyridine ligands is -6.2 kJ mol-1 when the entropy cost of bringing together the two molecules has already been paid by pyridine-zinc interactions. The development of template-directed approaches to the synthesis of nanorings with combinations of different metals at specific positions around the ring opens up many possibilities for controlling the photophysical behavior of these supramolecular systems and for probing their conformations by EPR.

Controlled intracellular generation of reactive oxygen species in human mesenchymal stem cells using porphyrin conjugated nanoparticles

Nanoparticles capable of generating controlled amounts of intracellular reactive oxygen species (ROS), that advance the study of oxidative stress and cellular communication, were synthesized by functionalizing polyacrylamide nanoparticles with zinc(II) porphyrin photosensitisers. Controlled ROS production was demonstrated in human mesenchymal stem cells (hMSCs) through (1) production of nanoparticles functionalized with varying percentages of Zn(II) porphyrin and (2) modulating the number of doses of excitation light to internalized nanoparticles. hMSCs challenged with nanoparticles functionalized with increasing percentages of Zn(II) porphyrin and high numbers of irradiations of excitation light were found to generate greater amounts of ROS. A novel dye, which is transformed into fluorescent 7-hydroxy-4-trifluoromethyl-coumarin in the presence of hydrogen peroxide, provided an indirect indicator for cumulative ROS production. The mitochondrial membrane potential was monitored to investigate the destructive effect of increased intracellular ROS production. Flow cytometric analysis of nanoparticle treated hMSCs suggested irradiation with excitation light signalled controlled apoptotic cell death, rather than uncontrolled necrotic cell death. Increased intracellular ROS production did not induce phenotypic changes in hMSC subcultures.

Photostable self-cleaning cotton by a copper(II) porphyrin/TiO2 visible-light photocatalytic system

Thin films of meso-tetra(4-carboxyphenyl)porphyrinato copper(II) (CuTCPP) in conjunction with anatase TiO2 have been formed on cotton fabric. Their self-cleaning properties have been investigated by conducting photocatalytic degradation of methylene blue, coffee and wine stains under visible-light irradiation. CuTCPP/TiO2-coated cotton fabrics showed superior self-cleaning performance when compared to bare TiO2-coated cotton. Furthermore, CuTCPP/TiO2-coated fabrics showed significant photostability under visible-light as compared to free base TCPP/TiO2-coated fabrics. The fabrics were characterized by FESEM, XRD and UV-vis spectroscopy. An insight into the mechanistic aspects of the CuTCPP/TiO2 photocatalysis is also discussed. Visible-light driven self-cleaning cotton based on copper(II) porphyrin/TiO2 catalyst exhibits significant potential in terms of stability and reproducibility for self-cleaning applications.

The redox chemistry of copper tetraphenylporphyrin revisited

Mixing Cu(II)Cl2 with free base tetraphenylporphyrin (( H2 (TPP)) in dry deaerated 1,2-dichloroethane surprisingly yields a mixture of Cu(II) (TPP) and Cu(III) (TPP). The later is long-lived in the absence of water and slowly decomposes within days to yield Cu(II) (TPP). Furthermore, in the presence of air, a slightly different CuIII porphyrin species forms, presumably, Cu(III) (TPP)•+, in which the Q-band is subject to a 10 nm red shift. The new Cu(III) (TPP) and Cu(III) (TPP)•+ differ in terms of absorption, fluorescence, electron paramagnetic resonance (EPR), and X-ray photoemission spectroscopy (XPS) when compared to the well-characterized Cu(II) (TPP), Cu(II) (TPP)•+, and Cu(II) (TPP)2+ species.

Unusual solvent dependent electronic absorption spectral properties of nickel(II) and copper(II) perhaloporphyrins

Electronic absorption spectra of divalent metal ( Ni (II) and Cu (II)) complexes of 2,3,7,8,12,13,17,18-octa(bromo/chloro)-5,10,15,20-tetraphenylporphyrins (MOXTPP; X = Br , Cl ) were examined in various solvents. M (II) perhaloporphyrins exhibited dramatic shifts in their optical absorption spectral features relative to the corresponding metallotetraphenylporphyrins, MTPPs. Copper(II) perhaloporphyrins show significant red-shifts of the absorption bands in coordinating solvents relative to that observed for nickel(II) perhaloporphyrins. The large red-shift of the electronic absorption bands and the gain in intensity of the longest wavelength band (Q(0,0)), of Cu (II) perhaloporphyrins in certain coordinating solvents is comparable to that found in meso-tetraphenylporphinatozinc(II), ZnTPP. The solvent dependent spectral features of M (II) perhaloporphyrins are attributed to a coordinative interaction of the solvent with the core metal ion induced by the electron deficient porphyrin macrocycle.

Metalloporphyrin anion sensors: the effect of the metal centre on the anion binding properties of amide-functionalised and tetraphenyl metalloporphyrins

This article describes the synthesis and anion binding properties of a series of 'picket fence' metalloporphyrin complexes, within which the metal centre is systematically varied. The porphyrin structure contains four amide bonds and is the same for each metal. The anion binding properties of these receptors are further contrasted with those of their tetraphenylporphyrin congeners to elucidate both the effect of the metal centre and the influence of the amide groups on the anion recognition process. Anion binding was demonstrated using UV/visible and (1)H NMR spectroscopies, electrochemistry and luminescence. The metal centre was found to be highly influential in the strength and selectivity of binding; for example, the cadmium and mercury complexes exhibited far greater affinities for anions than the zinc complexes in competitive solvents such as DMSO. The amide functionalities were found to enhance the anion binding process.