Belete B. Beyene

Oxasmaragdyrins as New and Efficient Hole-Transporting Materials for High-Performance Perovskite Solar Cells

The high performance of the perovskite solar cells (PSCs) cannot be achieved without a layer of efficient hole-transporting materials (HTMs) to retard the charge recombination and transport the photogenerated hole to the counterelectrode. Herein, we report the use of boryl oxasmaragdyrins (SM01, SM09, and SM13), a family of aromatic core-modified expanded porphyrins, as efficient hole-transporting materials (HTMs) for perovskite solar cells (PSCs). These oxasmaragdyrins demonstrated complementary absorption spectra in the low-energy region, good redox reversibility, good thermal stability, suitable energy levels with CH3NH3PbI3 perovskite, and high hole mobility. A remarkable power conversion efficiency of 16.5% (Voc = 1.09 V, Jsc = 20.9 mA cm-2, fill factor (FF) = 72%) is achieved using SM09 on the optimized PSCs device employing a planar structure, which is close to that of the state-of-the-art hole-transporting materials (HTMs), spiro-OMeTAD of 18.2% (Voc = 1.07 V, Jsc = 22.9 mA cm-2, FF = 74%). In contrast, a poor photovoltaic performance of PSCs using SM01 is observed due to the interactions of terminal carboxylic acid functional group with CH3NH3PbI3.

Photocatalytic hydrogen evolution from neutral aqueous solution by a water-soluble cobalt(II) porphyrin

Efficient storage of solar energy via light-driven hydrogen evolution is an attractive and promising strategy to address challenges related to increasing global energy demand. Herein, we report a highly active homogeneous photocatalytic hydrogen evolution system comprising a water-soluble cobalt(II) porphyrin, CoTPPS, as a molecular catalyst, [Ru(bpy)3]2+ as a photosensitizer, and ascorbic acid as a sacrificial electron donor. Under optimized conditions, a hydrogen evolution rate of 1.3 μmol min−1, a TOF of 120.8 min−1, and a TON of 6410 are obtained in 1 M phosphate buffer at pH 6.8 by irradiation with an LED light source at 420 nm and 0.6 W cm−2. The studies on the effects of pH and catalyst concentration showed that optimal H2 evolution efficiency was achieved at a pH of 6.8 and a catalyst concentration of 1.5 μM. Moreover, the kinetics of the fluorescence emission quenching experiment indicates that the rate of reductive quenching of [Ru(bpy)3]2+* by ascorbate (7.5 × 106 s−1) is higher than that of oxidative quenching by CoTPPS (1.7 × 104 s−1). As also supported by redox potential energy level analysis, a mechanistic pathway was proposed in which reduction of photo-excited [Ru(bpy)3]2+* by ascorbic acid produces [Ru(bpy)3]1+, which is a strong reductant and will subsequently reduce CoTPPS to generate cobalt-hydride for hydrogen evolution after protonation.

EPR and electrochemical interpretation of bispyrazolylacetate anchored Ni(II) and Mn(II) complexes: cytotoxicity and anti-proliferative activity towards human cancer cell lines

Two mononuclear NiII and MnII compounds, [Ni(bdtbpza)2(CH3OH)4] (1) and [Mn(bdtbpza)2(CH3OH)2(H2O)2] (2), are afforded by employing a ‘scorpionate’ type precursor [bdtbpza = bis(3,5-di-t-butylpyrazol-1-yl)acetate]. The single crystal X-ray structure reveals that the central metal ion (NiII for 1 and MnII for 2) is surrounded by a pair of Oacetate atoms of two bis(pyrazol-1-yl)acetate units, while four OMeOH donors for 1 and two OMeOH plus two Owater for 2 complete the first coordination sphere. Thus, both compounds exhibit a slightly distorted octahedral geometry possessing an O6 coordination environment. EPR spectra of CuII-doped 1 and of 2 recorded on the polycrystalline solids and in organic solution confirm the octahedral geometry around the metal ions and the binding of six oxygen atoms. The electrochemical study of compounds 1 and 2 shows that one electron reduction of MnII occurs at a more negative potential than NiII, indicating a lower tendency of reduction for Mn than Ni. Both compounds displayed a high cytotoxic activity against A2780 ovarian carcinoma cells and no cytotoxic activity in normal primary human fibroblasts for concentrations up to 55 μM. Notwithstanding, compound 1 is found to be the most cytotoxic towards A2780 cancer cells. The cytotoxic activity of compound 1 is correlated with the induction of apoptosis associated with a higher mitochondria dysfunction and autophagy cell death. In addition, the compounds can induce oxidative damage leading to ROS accumulation. Overall, the data presented here demonstrate that 1 has potential for further in vivo studies aiming at its future application in ovarian cancer therapy.