Zn-Porphyrin propped with hydantoin anchor: synthesis, photophysics and electron injection/recombination dynamics

Solar energy conversion using first row d-block metal coordination compound sensitizers and redox mediators

The use of renewable energy is essential for the future of the Earth, and solar photons are the ultimate source of energy to satisfy the ever-increasing global energy demands. Photoconversion using dye-sensitized solar cells (DSCs) is becoming an established technology to contribute to the sustainable energy market, and among state-of-the art DSCs are those which rely on ruthenium(ii) sensitizers and the triiodide/iodide (I3 -/I-) redox mediator. Ruthenium is a critical raw material, and in this review, we focus on the use of coordination complexes of the more abundant first row d-block metals, in particular copper, iron and zinc, as dyes in DSCs. A major challenge in these DSCs is an enhancement of their photoconversion efficiencies (PCEs) which currently lag significantly behind those containing ruthenium-based dyes. The redox mediator in a DSC is responsible for regenerating the ground state of the dye. Although the I3 -/I- couple has become an established redox shuttle, it has disadvantages: its redox potential limits the values of the open-circuit voltage (V OC) in the DSC and its use creates a corrosive chemical environment within the DSC which impacts upon the long-term stability of the cells. First row d-block metal coordination compounds, especially those containing cobalt, and copper, have come to the fore in the development of alternative redox mediators and we detail the progress in this field over the last decade, with particular attention to Cu2+/Cu+ redox mediators which, when coupled with appropriate dyes, have achieved V OC values in excess of 1000 mV. We also draw attention to aspects of the recyclability of DSCs.

Pyridyl/hydroxyphenyl versus carboxyphenyl anchoring moieties in Zn - Thienyl porphyrins for dye sensitized solar cells

For developing efficient DSCs, anchoring moieties need to be understood in detail with respect to a particular dye. Herein, we have synthesized new Zn-thienyl porphyrin dyes based on pyridyl and hydroxyphenyl anchors and compared with traditional carboxyphenyl anchoring group. The effect of such variation in anchoring groups was investigated with UV-vis and fluorescence spectroscopy as well as electrochemical studies. The hydroxyphenyl appended dye showed higher molar extinction coefficient and red shifted emission bands. Both pyridyl and hydroxyphenyl dyes showed adsorption over TiO₂ semiconductor. The dye loading amount was found to be greater for carboxyphenyl dye due to stronger bidendate coordination of the carboxy group, as revealed by FT-IR studies. The electrochemical potentials were found to be strongly influenced by the anchoring functionality and all the dyes showed positive driving force for electron injection to the conduction band of TiO₂ and regeneration of oxidized dye by the redox electrolyte. DSC devices were fabricated for each of the dyes and characterized well. Hydroxyphenyl dye showed higher V_oc as a result of lower back reactions. Transient photovoltage decay measurments indicated lower recombination rate in hydroxyphenyl and pyridyl than the carboxyphenyl anchored thienyl porphyrins offering potential for further dye optimization.

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.

Synthesis and electronic properties of A3B-thienyl porphyrins: experimental and computational investigations

A facile synthesis ofmeso-thienyl porphyrins containing a phenyl substituent allows fine tuning of the frontier orbitals to suit applications in DSSC and photomedicine.