Thin films of electropolymerized porphyrin polymers, poly-tetrakis-5,10,15,20-(4-aminophenyl)porphyrin (pTAPP) and its cobalt derivative (pCoTAPP), were found to be electrocatalysts and photoelectrocatalysts for the photosynthesis of hydrogen peroxide via a two-electron reduction of oxygen. On glassy carbon (GC) electrodes, oxygen reduction potentials were measured at −0.58 (GC), −0.40 (pTAPP), and −0.05 V (pCoTAPP), compared to Pt at +0.34 V (all vs Ag/AgCl). Thin electrode films were tested as photosynthetic electrocatalysts using small positive bias potentials (0.0 to +0.3 V) and specifically measuring H2O2 production. pTAPP achieved turnover numbers (TON) of 5–6, while pCoTAPP showed TON of 14–23. Faradaic efficiency in both cases was initially high, about 50%, but decreased over 1 h.

Two amphiphilic corroles—5,10,15-tris(3-carboxyphenyl)corrole (H3[mTCPC]) and 5,10,15-tris(4-carboxyphenyl)corrole (H3[pTCPC])—and their gold complexes have been synthesized, and their photophysical properties and photovoltaic behavior have been investigated. Like other nonpolar gold corroles, Au[mTCPC] and Au[pTCPC] were both found to exhibit room temperature phosphorescence in deoxygenated solutions with quantum yields of ∼0.3% and triplet lifetimes of ∼75 μs. Both compounds exhibited significant activity as dyes in photodynamic therapy experiments and in dye-sensitized solar cells. Upon irradiation at 435 nm, both Au corroles exhibited significant phototoxicity against AY27 rat bladder cancer cells while the free-base corroles proved inactive. Dye-sensitized solar cells constructed using the free bases H3[mTCPC] and H3[pTCPC] exhibited low efficiencies (≪1%), well under that obtained with 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin, H2[pTCPP] (1.9%, cf. N719 9.5%). Likewise, Au[pTCPC] proved inefficient, with an efficiency of ∼0.2%. By contrast, Au[mTCPC] proved remarkably effective, exhibiting an open-circuit voltage (Voc) of 0.56 V, a short-circuit current of 8.7 mA cm–2, a fill factor of 0.72, and an efficiency of 3.5%.

•Microinverters installed behind a PV panel can create a distinctive hot spot.•Rotation of the microinverter removes the distinctive hot spot on the panel.•Rotation of the microinverter allows the microinverter itself to run cooler.•Rotated (cooler) microinverters operate at slightly higher efficiency.Typical installation of a microinverter in a plane parallel position on the back side of a monocrystalline silicon photovoltaic (PV) panel can lead to differential heating of the PV cells immediately above the microinverter by as much as 4 °C. Rotation of the microinverter to a perpendicular position allows the microinverter itself to run cooler by about 4 °C and completely removes the distinctive heat signature on the panels. Because the thermal effects of the microinverters are significant for only two of the 72 cells on the panel, changes in DC power output from the panels are not detectable. However, lower microinverter temperatures increase microinverter efficiency by about 0.65%, such that overall AC power production is increased by about 0.09%. In addition to these small improvements to be gained by the repositioning of microinverters, there are also potential long-term concerns that nonuniform heating may lead to accelerated degradation in the affected area of the panel.

Titrations for a series of porphyrins bearing either 4-aminophenyl or 4-pyridyl meso substituents were performed using methanesulfonic acid in DMSO and followed by proton NMR. Special emphasis was placed on identifying the intermediate protonation stages that are described as hyperporphyrins, that is, where there exist strong charge-transfer interactions between the peripheral aminophenyl groups and the protonated porphyrin ring. In particular, evidence was gathered to support the significance of a novel resonance form involving charge transfer between two peripheral substituents, an aminophenyl group and a protonated pyridinium group. 1H NMR and NOESY spectra provide evidence for the importance of such resonance effects in the triply protonated triamino/monopyridyl hyperporphyrin (A3PyPH3+3).

5,10,15,20-Tetrakis(4-aminophenyl)porphyrin (TAPP) undergoes oxidative polymerization to form electronically conductive, nanofibrous structures in which the porphyrin units are linked by phenazine bridges. Polymerizations by chemical oxidation, electrochemical oxidation, and interfacial oxidative polymerization are described. Poly-TAPP (pTAPP) films have been characterized using scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and UV–vis spectroscopy. The polymer morphology is consistently nanofibrous, with some differences depending on the specific synthetic method. The polymer films show distinctive electrochromism at different redox and protonation states. A Pourbaix diagram correlates the proposed redox and protonation states of the polymer with applied potential, pH, and perceived color of the film. pTAPP shows the lowest resistance to oxidative doping/dedoping at low pH and potentials between +0.4 and +0.5 V vs Ag/AgCl.

Spectrophotometric titrations for a full series of 4-aminophenyl/4-pyridyl meso-substituted porphyrins were carried out using methanesulfonic acid in DMSO to study the hyperporphyrin effect across different substitution patterns. The series included zero, one, two (cis and trans), three, and four meso(4-aminophenyl) groups, with the remaining meso substituents being 4-pyridyl groups. The peripheral pyridyl groups consistently protonate before the interior porphyrin pyrrole nitrogens, which protonate before the aminophenyl groups. Aminophenyl substituents increase the basicity of the pyrrole nitrogens and lead to distinctive hyperporphyrin spectra with a broad Soret band and a strong red absorption. The structure proposed to give rise to these spectra is the previously proposed charge-transfer interaction between the aminophenyl and the protonated pyrrole. A novel hyperporphyrin structure involving charge-transfer interactions between two peripheral substituents is also proposed in one case, the triply protonated (+3) porphyrin with three aminophenyls and one pyridyl substituent; two of the aminophenyl groups delocalize the charges on the interior nitrogens, while the third aminophenyl group delocalizes with the protonated pyridyl.

Spectrophotometric titrations for a full series of para-amino/carbomethoxy-substituted tetraphenylporphyrins were carried out using methanesulfonic acid in DMSO to study the hyperporphyrin effect across different substitution patterns. The series included zero, one, two (cis and trans), three, and four amino groups, with the remaining para substituents carbomethoxy groups. With increasing numbers of aminophenyl groups, the relative basicity increased and the hyperporphyrin effect increased, marked by a strong red band and a split Soret band. The cis diamino derivative showed a stronger hyperporphyrin effect compared to the trans isomer, which can be explained based on simple resonance forms. For the monoamino derivative, an initial increase in the Soret band upon acid titration along with well-defined isosbestic points provided evidence for a monoprotonated porphyrin, distinct from the diprotonated and triprotonated states. The relative stability of this unusual intermediate is proposed to be due to charge delocalization of the first cation to the single amino group and destabilization of the second protonation by the electron-withdrawing carbomethoxy substituents.

A dye-sensitized solar cell was constructed using a porphyrin photosensitizer and, in place of the usual iodide redox system, a solution in aniline solvent containing lithium perchlorate electrolyte, camphorsulfonic acid, and poly(ethylene oxide) copolymer. Irradiation generated polyaniline within the cell, initially following a proposed photoelectropolymerization mechanism, and eventually operating as a solar cell with polyaniline as the hole transport medium. Overall energy conversion efficiency was 0.8% at moderate light intensities (14.6 mW cm−2) but lower at higher light intensities due to conductivity limitations.

Porphyrins have been studied as photosensitizers in two different types of solar cells. In one type of cell, a p–n junction was created with the system ITO/5,10,15,20-tetra(o-nitrophenyl)porphyrinatozinc/Alq3/Al. In another type of cell, porphyrins with carboxyphenyl and aminophenyl substituents were used as photosensitizers for a nanoparticulate TiO2 (Grätzel) cell in which photoelectropolymerization of aniline created polyaniline as a hole transport medium. Optimum results from such cells gave an open-circuit voltage (Voc) of 0.6 V, a short-circuit current (Jsc) of 0.2 mA/cm2, a fill factor of 0.7, and a conversion efficiency of 2.4% under 4.4 mW/cm2 of simulated solar intensity. Such cells offer a promising new approach to a solid-state Grätzel cell.