Carboxyphenyl Metalloporphyrins as Photosensitizers of Semiconductor Film Electrodes. A Study of the Effect of Different Central Metals

Porphyrin-BODIPY Dyad: Enhancing Photodynamic Inactivation via Antenna Effect

A porphyrin-BODIPY dyad (P-BDP) was obtained through covalent bonding, featuring a two-segment design comprising a light-harvesting antenna system connected to an energy acceptor unit. The absorption spectrum of P-BDP resulted from an overlap of the individual spectra of its constituent parts, with the fluorescence emission of the BODIPY unit experiencing significant quenching (96 %) due to the presence of the porphyrin unit. Spectroscopic, computational, and redox investigations revealed a competition between photoinduced energy and electron transfer processes. The dyad demonstrated the capability to sensitize both singlet molecular oxygen and superoxide radical anions. Additionally, P-BDP effectively induced the photooxidation of L-tryptophan. In suspensions of Staphylococcus aureus cells, the dyad led to a reduction of over 3.5 log (99.99 %) in cell survival following 30 min of irradiation with green light. Photodynamic inactivation caused by P-BDP was also extended to the individual bacterium level, focusing on bacterial cells adhered to a surface. This dyad successfully achieved the total elimination of the bacteria upon 20 min of irradiation. Therefore, P-BDP presents an interesting photosensitizing structure that takes advantage of the light-harvesting antenna properties of the BODIPY unit combined with porphyrin, offering potential to enhance photoinactivation of bacteria.

Two spectral QSPR models of porphyrin macromolecules for chelating heavy metals and different ligands released from industrial solvents: CH2Cl2, CHCl3 and toluene

Two simple and reliable correlations are introduced for the prediction of emission and absorption of porphyrins and their derivatives, i.e. metalloporphyrins and ligand coordinated metalloporphyrins. They can be used to sense the extracted precious metals. The proposed models require only simple structural parameters such as the number of carbon, metal and metal-free molecular fragments of desirable porphyrins or their derivatives. Since the proposed models depend on molecular structures of the desired compounds, they can be easily applied for complex molecular structures. Experimental data of 272 porphyrin derivatives were used to derive and test the novel models for the assessment of their emission (Em.) and absorption (Abs.) values in three solvents namely dichloromethane, toluene and chloroform. The values of the coefficients of determination (r ²) for the training set (183 compounds) in dichloromethane and three different test sets, corresponding to the three mentioned solvents, for the emission and absorption correlations were greater than 0.70. The calculated values of the root-mean-square error (RMSE) for the training sets of Em. and Abs. correlations were equal to 7.56 and 4.86 nm, respectively. Further statistical parameters also confirm the high reliability of the new models.

Synthesis, photophysical characterization, and photoelectrochemical evaluation of a palladium porphyrin sensitizer for TiO2-based dye-sensitized solar cells

An unsymmetrical (A3B) palladium porphyrin bearing a cyanoacrylic acid at one meso position has been synthesized for evaluation as a photosensitizer in dye-sensitized solar cells based on titanium dioxide ( TiO 2) as a comparison to other metalloporphyrins and as a proxy for other potential triplet-state photosensitizer compounds. The synthesis of this palladium porphyrin has provided new insight into the mechanism and product distribution of decarboxylative hydrolysis of malonic acid when attached at the porphyrin meso position. A crystal structure determination for a meso-formyl palladium porphyrin has been determined, showing saddle-distortion of the porphyrin core. The photophysical behavior of the palladium porphyrin sensitizer and its performance in photoelectrochemical cells are described and interpreted in the context of bimolecular excited state quenching pathways including oxygen sensitization, triplet–triplet annihilation and electron transfer events. Palladium porphyrins are proposed as a sensitizer class with potential for high efficiency dye-sensitized solar cells, but with the caveat that some overpotential for electron injection is necessary to compete against the multiple decay pathways that are specially available to triplet state photosensitizers.

Photodynamic inactivation of bacteria using novel electrogenerated porphyrin-fullerene C60 polymeric films

A porphyrin-fullerene C60 dyad (TCP-C60) substituted by carbazoyl groups was used to obtain electrogenerated polymeric films on optically transparent indium tin oxide (ITO) electrodes. This approach produced stable and reproducible polymers, holding fullerene units. The properties of this film were compared with those formed by layers of TCP/TCP-C60 and TCP/ZnTCP. Absorption spectra of the films presented the Soret and Q bands of the corresponding porphyrins. The TCP-C60 film produced a high photodecomposition of 2,2-(anthracene-9,10-diyl)bis(methylmalonate), which was used to detect singlet molecular oxygen O2((1)Δg) production in water. In addition, the TCP-C60 film induced the reduction of nitro blue tetrazolium to diformazan in the presence of NADH, indicating the formation of superoxide anion radical. Moreover, photooxidation of L-tryptophan mediated by TCP-C60 films was found in water. In biological media, photoinactivation of Staphylococcus aureus was evaluated depositing a drop with 2.5 × 10(3) cells on the films. After 30 min irradiation, no colony formation was detected using TCP-C60 or TCP/TCP-C60 films. Furthermore, photocytotoxic activity was observed in cell suspensions of S. aureus and Escherichia coli. The irradiated TCP-C60 film produced a 4 log decrease of S. aureus survival after 30 min. Also, a 4 log reduction of E. coli viability was obtained using the TCP-C60 film after 60 min irradiation. Therefore, the TCP-C60 film is an interesting and versatile photodynamic active surface to eradicate bacteria.

Photophysical and electrochemical properties, and molecular structures of organic dyes for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) based on organic dyes adsorbed on oxide semiconductor electrodes, such as TiO(2), ZnO, or NiO, which have emerged as a new generation of sustainable photovoltaic devices, have attracted much attention from chemists, physicists, and engineers because of enormous scientific interest in not only their construction and operational principles, but also in their high incident-solar-light-to-electricity conversion efficiency and low cost of production. To develop high-performance DSSCs, it is important to create efficient organic dye sensitizers, which should be optimized for the photophysical and electrochemical properties of the dyes themselves, with molecular structures that provide good light-harvesting features, good electron communication between the dye and semiconductor electrode and between the dye and electrolyte, and to control the molecular orientation and arrangement of the dyes on a semiconductor surface. The aim of this Review is not to make a list of a number of organic dye sensitizers developed so far, but to provide a new direction in the epoch-making molecular design of organic dyes for high photovoltaic performance and long-term stability of DSSCs, based on the accumulated knowledge of their photophysical and electrochemical properties, and molecular structures of the organic dye sensitizers developed so far.

Porphyrin-rhodanine dyads for dye sensitized solar cells

A series of four new porphyrin-rhodanine dyads were synthesized having the rhodanine acetic acid group either at the meso- or the pyrrole-β position of a free-base/zinc porphyrin. These dyads were fully characterized by UV-visible, 1 H NMR, MALDI-MS and fluorescence spectroscopies and cyclic voltammetry. Both the Soret and Q-bands were red-shifted in the case of pyrrole-β substituted dyads. The redox potentials of all four dyads were altered in comparison with their individual constituents. The dyads were tested in dye sensitized solar cells and the zinc metalated dyads gave a better performance in comparison with the corresponding free-base dyads.

Synthesis of novel porphyrin and chlorin phosphonic acids and their immobilization on metal oxides

In this study an easy and flexible access to porphyrin and chlorin phosphonic acids is presented. Novel types of phosphonic acid terminated porphyrins and chlorins were synthesized starting from commercially available red blood pigment hemin chloride. Phosphonic acid groups were linked to the porphyrinoids by amide coupling via appropriate spacer moieties. Self-assembled monolayers of the synthesized phosphonates on mesoporous TiO2 electrodes of approximately 3 μm thickness were formed. Surface concentrations in a range of 1 to 4 × 10-8 mol.cm-2 could be determined by UV-vis spectroscopy.

Metal insertion into phosphonic acid terminated porphyrins immobilized on TiO2 electrodes

In this study an easy access for modification of properties of porphyrin covered TiO2 electrodes by post-assembling metal insertion was investigated. Therefore a new type of phosphonic acid terminated porphyrin was synthesized and immobilized on mesoporous TiO2 electrodes by self-assembling. Surface concentrations in a range of 1.5–3.3 × 10-8 mol.cm-2, based on the geometric area, were obtained by two independent techniques, UV-vis and cyclic voltammetry. Co(II) , Zn(II) , Pd(II) and Mn(III) ions could be inserted into the immobilized porphyrin by exposing the electrode to a boiling solution of metal chloride in methanol. The electrode surface was characterized by UV-vis spectroscopy and cyclic voltammetry before and after metal insertion. The electrocatalytic activity towards the reduction of molecular oxygen in acidic solution was examined, further confirming metal insertion into immobilized porphyrin monolayer.

Synthesis and the electron transfer reaction of (metallo)-porphyrin linked with a fullerene through an (L)-lysine spacer

A novel visible-light induced electron transfer system composed of the free-base or Zn porphyrin, C60 molecule, and an (L)-lysine was synthesized and characterized. The porphyrin and C60 were covalently linked by the amide bonds through a relatively long and flexible spacer, (L)-lysine. The 1H NMR spectrum of the Zn porphyrin/(L)-lysine/ C60 conjugate (3Zn) suggested that C60 caused the slow molecular motion of this molecule. The steady-state absorption and the emission spectra of 3Zn revealed the intramolecular excited-state electron transfer from the Zn porphyrin moiety to the C60 moiety. The fluorescent lifetime measurement of the excited-state Zn porphyrin in 3Zn indicated the quenching by C60 . The intermolecular electron transfer from the excited-state zinc porphyrin to the viologen derivative in the solution was examined. The Zn porphyrin/(L)-lysine/ C60 conjugate and the free-base porphyrin/(L)-lysine/ C60 conjugate were more effective catalysts than the tetraphenylporphyrin Zn complex, suggesting the intermediacy of the charge separation state, ZnP·+-C60·- .

Photodynamic properties and photoantimicrobial action of electrochemically generated porphyrin polymeric films

Spectroscopic and photodynamic properties of polymeric films bearing porphyrin units have been studied in both solution containing photooxidizable substrates and in vitro on Escherichia coli and Candida albicans microorganisms. The films were formed by electrochemical polymerization of 5,10,15,20-tetra(4-N,N-diphenylaminophenyl)porphyrin (H2P-film) and its complex with Pd(II) (PdP-film) on optically transparent indium tin oxide (ITO) electrodes. Absorption spectroscopic studies show the characteristic Soret and Q bands of the porphyrin in the visible region and a band at approximately 350 nm corresponding to the tetraphenylbenzidine units. Upon excitation, the H2P-film exhibits two bands of fluorescence emission from porphyrin, while it is not detected using PdP-film. The singlet molecular oxygen, O2(1Deltag), productions of these surfaces were evaluated using 9,10-dimethylanthracene in N,N-dimethylformamide. Also, the photodynamic activity was compared in solutions of L-tryptophan. Under these conditions, oxidation of these substrates takes place indicating an efficient photodynamic action of both polymeric films. In vitro investigations show that these films produce photosensitized inactivation of microbial cells in aqueous suspensions. These films exhibit a photosensitizing activity causing a approximately 3 log decrease of E. coil and approximately 2.5 log of C. albicans cellular survival after 30 min of irradiation with visible light. The photodynamic effect of the surfaces was also tested by growth delay experiments. The results indicate that porphyrins immobilized on electropolymeric films are interesting and versatile photodynamic surfaces to inactivate microorganisms in liquid suspensions.

Parameters affecting the chemical work output of a hybrid photoelectrochemical biofuel cell

A hybrid photoelectrochemical biofuel cell employing the photoanode architecture of a dye-sensitized solar cell has been assembled. A porphyrin dye sensitizes a TiO(2) semiconductor over the visible range to beyond 650 nm. Photoinduced charge separation at the dye-TiO(2) interface results in electron migration to a cathode, and the holes generated on surface bound dyes oxidize soluble electron mediators. The increased [Ox] : [Red] ratio of the mediator drives the solution-based enzymatic oxidation of appropriate substrates. In this report we investigate how the accumulation of anodic and cathodic products limits cell performance. The NAD(+)/NADH and benzoquinone/hydroquinone redox couples were studied as sacrificial electron donors in the absence of appropriate enzymes or substrates. Comparatively poor cell performance was observed using the benzoquinone/hydroquinone couple. This effect is explained in terms of rapid charge recombination by electron donation from the electrode to benzoquinone in solution, as compared to much less recombination with NAD(+). With the NAD(+)/NADH couple the cell performance is relatively independent of the redox poise of the anode solution, but limited by accumulation of reduction products in the cathodic compartment. Using the NAD(+)/NADH couple, the photochemical reforming of ethanol to hydrogen was demonstrated under conditions where the process would be endergonic in the dark.