Zinc Meso-tetrakis Research Articles

Study on the zinc porphyrins as potential carbonic anhydrase mimics for promoting CO2 absorption in K2CO3 solution

Zinc porphyrins, boasting a coordination environment akin to that of natural carbonic anhydrase (CA), coupled with excellent structural stability, built-in hydrophobic pocket, and suitable charge of center Zn2+, were considered as potential CA-mimics for CO2 capture. To validate this assumption, three zinc porphyrin representatives, zinc porphin (ZnP), zinc protoporphyrin IX (ZnPP), and zinc meso-tetrakis(N-methylpyridinium-4-yl) porphyrin (ZnTMPyP), were prepared, and tested performance in enhancing CO2 absorption in water and K2CO3 solutions. The results from CO2 absorption experiments indicated that ZnTMPyP with the optimal dosage increased CO2 absorption rate by 44.25 % in water, and ZnPP with the optimal dosage increased the CO2 absorption rate by 63.67 % in 20 wt% of K2CO3 solution, which are respectively 1.53 and 2.07 times of CO2 absorption performance of zinc cyclen (ZnC), the most effective CA-mimic reported. Besides, the zinc porphyrins demonstrated excellent stability and reusability throughout five cycles of CO2 absorption and desorption, which are vital aspects for practical applications. Through the calorimetric method and density functional theory (DFT) calculations, it was confirmed that the prepared zinc porphyrins had similar enzymatic behavior and catalytic CO2 hydration pathway to natural CA. According to the results of characterization and DFT calculations, high dispersion, the lowest charge of the Zn2+ center, and the existence of additional CO2 adsorption sites (propionate ions), endow ZnPP with the highest catalytic activity in the K2CO3 solution.

Large work function shift of organic semiconductors inducing enhanced interfacial electron transfer in organic optoelectronics enabled by porphyrin aggregated nanostructures

We report on large work function shifts induced by the coverage of several organic semiconducting (OSC) films commonly used in organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs) with a porphyrin aggregated layer. The insertion between the organic film and the aluminum cathode of an aggregated layer based on the meso-tetrakis(1-methylpyridinium-4-yl) porphyrin chloride (porphyrin 1), with its molecules adopting a face-to-face orientation parallel to the organic substrate, results in a significant shift of the OSC work function towards lower values due to the formation of a large interfacial dipole and induces large enhancement of either the OLED or OPV device efficiency. OLEDs based on poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-2,1′,3-thiadiazole)] (F8BT) and incorporating the porphyrin 1 at the cathode interface exhibited current efficiency values up to 13.8 cd/A, an almost three-fold improvement over the efficiency of 4.5 cd/A of the reference device. Accordingly, OPVs based on poly(3-hexylthiophene) (P3HT), [6,6]-phenyl-C61 butyric acid methyl ester (PC61BM) and porphyrin 1 increased their external quantum efficiencies to 4.4% relative to 2.7% for the reference device without the porphyrin layer. The incorporation of a layer based on the zinc meso-tetrakis (1-methylpyridinium-4-yl)porphyrin chloride (porphyrin 2), with its molecules adopting an edge-to-edge orientation, also introduced improvements, albeit more modest in all cases, highlighting the impact of molecular orientation.

Photocatalytic hydrogen production from a noble metal free system based on a water soluble porphyrin derivative and a cobaloxime catalyst

A combination of noble-metal free components, a water soluble porphyrin photosensitizer zinc meso-tetrakis(1-methylpyridinium-4-yl)porphyrin chloride [ZnTMPyP(4+)]Cl4 (1) with cobaloxime complex [Co(III)(dmgH)2(py)Cl] (2) as a catalyst, creates an efficient system for photochemical hydrogen production acting under visible light with 280 TONs. This is the first example of a water soluble porphyrin acting as a photosensitizer for cobaloxime catalysed H2 production.

NEXAFS Study of Zinc Porphyrins Intercalated into V2O5 Xerogel

For the first time the NEXAFS N1sand C1sspectra of composites on the basis of macrocyclic molecules zinc meso-tetrakis(4-pyridyl)porphyrin, zinc meso-tetrakis(N-methylpyridinium-4-yl)porphyrin tetraiodide and V2O5·nH2O xerogel were studied by a total electron yield method with using synchrotron radiation of Russian-Germany beamline at BESSY-II. These intercalation complexes are insoluble in water, stable and exhibit good electrochemical properties. The host-guest interaction leads to the great changes of NEXAFS N1sand C1s-spectra of the synthesized composites as compared with pristine compounds spectra. The studies show the 2.1 eV blue shift energy position and great increase oscillator strength of the π-resonance in the NEXAFS N1sspectra of pyridine cycle when ZnPor(Py)4 intercalated into V2O5·nH2O xerogel.

Porphyrin “Mille-Feuilles” photo-electrodes

A porphyrin “Mille-Feuilles” photo-electrode is fabricated layer-by-layer by deposition of anionic [zinc meso-tetrakis( p-sulfonatophenyl) porphyrin] 4− (ZnTPPS 4−) and positively charged polypeptides on a 11-mercaptoundecanoic acid-modified gold electrode to form a photoactive film. This work demonstrates that it is possible to form 3D structures having regularly spaced layers of redox molecules. UV–visible spectra of the multilayer films display the characteristic absorption bands of the porphyrins and the absorbance increases linearly with the number of bilayers. The cyclic voltammetric response of the films in contact with 1,2-dichloroethane (DCE) varies from that of a modified electrode to that of a supported liquid film. Under illumination, a large photocurrent response for oxygen reduction with a maximum for a 5-bilayer film is observed.

Fluorescence quenching of the S1 and S2 states of zinc meso-tetrakis(4-sulfonatophenyl)porphyrin by halide ions.

The excited-state quenching of zinc meso-tetrakis(4-sulfonatophenyl)porphyrin (ZnTPPS) by halide ions has been studied in water and various aqueous micellar solutions using both steady-state and time-resolved fluorescence techniques. The quenching efficiencies of the S(1) state of ZnTPPS ([small tau][approximate] 1.93 ns) by halide ions in homogeneous aqueous solution increase in the order Cl(-) < Br(-) < I(-); both dynamic and static quenching processes are involved. The mechanisms which may possibly be operating (i.e. electron transfer, heavy atom effect and Watkins mechanism) are discussed. Quenching of the short-lived S(2) state ([small tau][approximate] 1.3 ps) of ZnTPPS is only possible using I(-); it is suggested that the quenching mechanism proceeds via electron transfer between the fluorophore and I(-) within the quenching sphere of action. The results are consistent with the Gibbs free energy change ([capital Delta]G[degree]) involved in the charge-separation process. Finally, the fluorescence quenching of ZnTPPS by bromide ions in both cationic (DTAB and CTAC) and neutral (TX-100) micelles has been examined. The quenching observed in the cationic micelles is rationalised using a water-filled channel model, whereby Br(-) ions diffuse down these channels to achieve close proximity to the fluorophore. No emission quenching was observed in the case of the neutral TX-100 micelles.

Photoinduced electron transfer at liquid|liquid interfaces: dynamics of the heterogeneous photoreduction of quinones by self-assembled porphyrin ion pairs.

The initial stages of the heterogeneous photoreduction of quinone species by self-assembled porphyrin ion pairs at the water|1,2-dichloroethane (DCE) interface have been studied by ultrafast time-resolved spectroscopy and dynamic photoelectrochemical measurements. Photoexcitation of the water-soluble ion pair formed by zinc meso-tetrakis(p-sulfonatophenyl)porphyrin (ZnTPPS(4)(-)) and zinc meso-tetrakis(N-methylpyridyl)porphyrin (ZnTMPyP(4+)) leads to a charge-separated state of the form ZnTPPS(3)(-)-ZnTMPyP(3+) within 40 ps. This charge-separated state is involved in the heterogeneous electron injection to acceptors in the organic phase in the microsecond time scale. The heterogeneous electron transfer manifests itself as photocurrent responses under potentiostatic conditions. In the case of electron acceptors such as 1,4-benzoquinone (BQ), 2,6-dichloro-1,4-benzoquinone (DCBQ), and tetrachloro-1,4-benzoquinone (TCBQ), the photocurrent responses exhibit a strong decay due to back electron transfer to the oxidized porphyrin ion pair. Interfacial protonation of the radical semiquinone also contributes to the photocurrent relaxation in the millisecond time scale. The photocurrent responses are modeled by a series of linear elementary steps, allowing estimations of the flux of heterogeneous electron injection to the acceptor species. The rate of electron transfer was studied as a function of the thermodynamic driving force, confirming that the activation energy is controlled by the solvent reorganization energy. This analysis also suggests that the effective redox potential of BQ at the liquid|liquid boundary is shifted by 0.6 V toward positive potentials with respect to the value in bulk DCE. The change of the redox potential of BQ is associated with the formation of hydrogen bonds at the liquid|liquid boundary. The relevance of this approach toward modeling the initial processes in natural photosynthetic reaction centers is briefly discussed.

Photocurrent responses at dye sensitised ultrathin polyelectrolyte multilayers supported on gold electrodes.

The photoelectrochemical behaviour of ionic conducting ultrathin multilayers formed by sequential deposition of poly-L-lysine and poly-L-glutamic acid on modified gold electrodes is investigated upon sensitisation by zinc mesotetrakis(p-sulfonatophenyl)porphyrin.

Excited state quenching kinetics of zinc meso-tetrakis (N-methylpyridinium-4-yl) porphyrin by methyl viologen in AOT reverse micelles

The singlet and triplet excited state quenching of Zn (II) meso-tetrakis (N-methylpyridinum-4-yl) porphyrin (ZnTMPyP4+) by methyl viologen (Mv2+) in AOT reverse micelles has been studied using steady state fluorescence and laser flash photolysis techniques. The water content in the reverse micelle was varied by using different values of W0 = [H2O]/[AOT] at fixed AOT (0.1 M) concentration and the quenching process efficiency was found to decrease with increasing W0. The ZnTMPyP4+ triplet state is strongly quenched by Mv2+ and the probe decay profiles were nonexponential. Data analysis with an active sites quenching model gave aggregation numbers which compare well with the literature values reported for the AOT reverse micelles. The rate constants for the quenching of singlet and triplet excited states correlate with the micelle size and were found to decrease with increasing micellar radii giving evidence of a geometrical confinement effect. The magnitudes of the rate constants are of the order of diffusion controlled reactions affected by electrostatic interactions between charged species in the interfacial micellar region.

Photoinduced Electron Transfer at Liquid/Liquid Interfaces. Part III. Photoelectrochemical Responses Involving Porphyrin Ion Pairs

The interfacial photoreactivity of water soluble porphyrin ion pairs was explored by photocurrent measurements at the water/1,2-dichloroethane interface. The anionic zinc meso-tetrakis(p-sulfonatop...

Formation and decay of zinc tetrakis (N-methyl-3-pyridyl)porphine π-radical cation in water

Zinc meso-tetrakis(N-methyl-3-pyridyl)porphine [ZnTMPyP(3)4+] is readily oxidised to the π-radical cation under pulse radiolytic ([KBr]= 10–2 mol dm–3) or photochemical ([S2O2–8]= 10–3 mol dm–3) conditions. The π-radical cation undergoes bimolecular disproportionation to form a porphyrin π-dication which reacts with hydroxide ions to form an isoporphyrin (pH < 7) or a 5,6-dihydroxyporphyrin (pH > 7). This disproportionation reaction can be catalysed by colloidal RuO2·2H2O and Prussian Blue, but at pH > 7, the catalysed reaction leads to competitive formation of a ring-opened product. Photolysis (λ > 420 nm) of ZnTMPyP(3)4+ in water containing persulphate and catalyst does not result in generation of detectable amounts of O2.