Photoluminescence Switching in Quantum Dots Connected with Carboxylic Acid and Thiocarboxylic Acid End-Group Diarylethene Molecules.

We contrast the switching of photoluminescence (PL) of PbS quantum dots (QDs) cross-linked with photochromic diarylethene molecules with different end groups, 4,4'-(1-cyclopentene-1,2-diyl)bis[5-methyl-2-thiophenecarboxylic acid] () and 4,4'-(1-cyclopentene-1,2-diyl)bis[5-methyl-2-thiophenethiocarboxylic acid] (). Our results show that the QDs cross-linked with the carboxylic acid end group molecules () exhibit a greater amount of switching in photoluminescence intensity compared to QDs cross-linked with the thiocarboxylic acid end group (). We also demonstrate that regardless of the molecule used, greater switching amounts are observed for smaller quantum dots.

Developing homogeneous first row early transition metal catalysts for the oxygen reduction reaction.

The oxygen reduction reaction (ORR) remains an important fixture in biological and synthetic systems for energy conversion and chemical functionalization. Late transition metals continue to dominate in the development of new catalyst systems, inspired by well-characterized metallocofactors and prior successes. By comparison, metals to the left of Fe on the periodic table are relatively understudied for the ORR.

Acid Strength Effects on Dimerization during Metal-Free Catalytic Dioxygen Reduction.

Development of earth-abundant catalysts for the reduction of dioxygen (ORR) is essential for the development of alternative industrial processes and energy sources. Here, we report a transition metal-free dicationic organocatalyst () for the ORR. The ORR performance of this compound was studied in acetonitrile solution under both electrochemical conditions and spectrochemical conditions, using halogenated acetic acid derivatives spanning a p range of 12.

Pre-equilibrium reactions involving pendent relays improve CO reduction mediated by molecular Cr-based electrocatalysts.

Homogeneous earth abundant transition-metal electrocatalysts capable of carbon dioxide (CO) reduction to generate value-added chemical products are a possible strategy to minimize rising anthropogenic CO emissions. Previously, it was determined that Cr-centered bipyridine-based NO complexes for CO reduction are kinetically limited by a proton-transfer step during C-OH bond cleavage. Therefore, it was hypothesized that the inclusion of pendent relay groups in the secondary coordination sphere of these molecular catalysts could increase their catalytic activity.

Design of Cr-Based Molecular Electrocatalyst Systems for the CO Reduction Reaction.

ConspectusHuman influence on the climate system was recently summarized by the sixth Intergovernmental Panel on Climate Change (IPCC) Assessment Report, which noted that global surface temperatures have increased more rapidly in the last 50 years than in any other 50-year period in the last 2000 years. Elevated global surface temperatures have had detrimental impacts, including more frequent and intense extreme weather patterns like flooding, wildfires, and droughts. In order to limit greenhouse gas emissions, various climate change policies, like emissions trading schemes and carbon taxes, have been implemented in many countries.

Improving co-electrocatalytic carbon dioxide reduction by optimizing the relative potentials of the redox mediator and catalyst.

The effects of fixing the redox mediator (RM) reduction potential relative to a series of Cr-centered complexes capable of the reduction of CO to CO are disclosed. The greatest co-electrocatalytic activity enhancement is observed when the reduction potentials of the catalyst and RM are identical, implying that controlling the speciation of the Cr complex relative to RM activation is essential for improving catalytic performance. In all cases, the potential where co-catalytic activity is observed matches the reduction potential of the RM, regardless of the relative reduction potential of the Cr complex.

Controlling product selectivity during dioxygen reduction with Mn complexes using pendent proton donor relays and added base.

The catalytic reduction of dioxygen (O) is important in biological energy conversion and alternative energy applications. In comparison to Fe- and Co-based systems, examples of catalytic O reduction by homogeneous Mn-based systems is relatively sparse. Motivated by this lack of knowledge, two Mn-based catalysts for the oxygen reduction reaction (ORR) containing a bipyridine-based non-porphyrinic ligand framework have been developed to evaluate how pendent proton donor relays alter activity and selectivity for the ORR, where Mn(dhbpy)Cl (1) was used as a control complex and Mn(dhbpy)Cl (2) contains a pendent -OMe group in the secondary coordination sphere.

Metal-Free Homogeneous O Reduction by an Iminium-Based Electrocatalyst.

The oxygen reduction reaction (ORR) is important for alternative energy and industrial oxidation processes. Herein, an iminium-based organoelectrocatalyst () for the ORR with trifluoroacetic acid as a proton source in acetonitrile solution under both electrochemical and spectrochemical conditions using decamethylferrocene as a chemical reductant is reported. Under spectrochemical conditions, HO is the primary reaction product, while under electrochemical conditions HO is produced.

Photoluminescence switching in quantum dots connected with fluorinated and hydrogenated photochromic molecules.

We investigate switching of photoluminescence (PL) from PbS quantum dots (QDs) crosslinked with two different types of photochromic diarylethene molecules, 4,4'-(1-cyclopentene-1,2-diyl)bis[5-methyl-2-thiophenecarboxylic acid] (1H) and 4,4'-(1-perfluorocyclopentene-1,2-diyl)bis[5-methyl-2-thiophenecarboxylic acid] (2F). Our results show that the QDs crosslinked with the hydrogenated molecule (1H) exhibit a greater amount of switching in photoluminescence intensity compared to QDs crosslinked with the fluorinated molecule (2F). With a combination of differential pulse voltammetry and density functional theory, we attribute the different amount of PL switching to the different energy levels between 1H and 2F molecules which result in different potential barrier heights across adjacent QDs.

Sterically attenuated electronic communication in cobalt complexes of meridional isoquinoline-derived ligands for applications in electrocatalysis.

The ability to synthetically tune the ligand frameworks of redox-active molecules is of critical importance to the economy of solar fuels because manipulating their redox properties can afford control over the operating potentials of sustained electrocatalytic or photoelectrocatalytic processes. The electronic and steric properties of 2,2':6',2″-terpyridine (Terpy) ligand frameworks can be tuned by functional group substitution on ligand backbones, and these correlate strongly to their Hammett parameters. The synthesis of a new series of tridentate meridional ligands of 2,4,6-trisubstituted pyridines that engineers the ability to finely tune the redox potentials of cobalt complexes to more positive potentials than that of their Terpy analogs is achieved by aryl-functionalizing at the four-position and by including isoquinoline at the two- and six-positions of pyridine (Aryl-DiQ).

Solution Shearing of Zirconium (Zr)-Based Metal-Organic Frameworks NU-901 and MOF-525 Thin Films for Electrocatalytic Reduction Applications.

Solution shearing, a meniscus-guided coating process, can create large-area metal-organic framework (MOF) thin films rapidly, which can lead to the formation of uniform membranes for separations or thin films for sensing and catalysis applications. Although previous work has shown that solution shearing can render MOF thin films, examples have been limited to a few prototypical systems, such as HKUST-1, Cu-HHTP, and UiO-66. Here, we expand on the applicability of solution shearing by making thin films of NU-901, a zirconium-based MOF.

Correction: Co-electrocatalytic CO reduction mediated by a dibenzophosphole oxide and a chromium complex.

Correction for 'Co-electrocatalytic CO reduction mediated by a dibenzophosphole oxide and a chromium complex' by Connor A. Koellner , , 2023, https://doi.org/10.

Co-electrocatalytic CO reduction mediated by a dibenzophosphole oxide and a chromium complex.

We report a co-electrocatalytic system for the selective reduction of CO to CO, comprised of a previously reported molecular Cr complex and 5-phenylbenzo[]phosphindole-5-oxide (PhBPO) as a redox mediator. Under protic conditions, the co-electrocatalytic system attains a turnover frequency (TOF) of 15 s and quantitative selectivity for CO. It is proposed that PhBPO interacts with the Cr-based catalyst, coordinating in an axial position to an intermediate hydroxycarbonyl species, M-COH, mediating electron transfer to the catalyst and lowering the barrier for C-OH bond cleavage.

Redox Mediators in Homogeneous Co-electrocatalysis.

Homogeneous electrocatalysis has been well studied over the past several decades for the conversion of small molecules to useful products for green energy applications or as chemical feedstocks. However, in order for these catalyst systems to be used in industrial applications, their activity and stability must be improved. In naturally occurring enzymes, redox equivalents (electrons, often in a concerted manner with protons) are delivered to enzyme active sites by small molecules known as redox mediators (RMs).

Homogeneous Electrocatalytic Reduction of CO by a CrNO Complex: Electronic Coupling with a Redox-Active Terpyridine Fragment Favors Selectivity for CO.

Electrocatalyst design and optimization strategies continue to be an active area of research interest for the applied use of renewable energy resources. The electrocatalytic conversion of carbon dioxide (CO) is an attractive approach in this context because of the added potential benefit of addressing its rising atmospheric concentrations. In previous experimental and computational studies, we have described the mechanism of the first molecular Cr complex capable of electrocatalytically reducing CO to carbon monoxide (CO) in the presence of an added proton donor, which contained a redox-active 2,2'-bipyridine (bpy) fragment, CrNO.

Homogeneous catalysis of dioxygen reduction by molecular Mn complexes.

Continually increasing global energy demand perpetuates the need for effective alternative energy sources and 'green' industrial processes. The oxygen reduction reaction (ORR) is crucial to the development of hydrogen fuel cells, a key device in the development of alternative energy sources. Further, the ORR to hydrogen peroxide by electrochemical means can provide an environmentally friendly alternative to its industrial production, which is capital and energy intensive.

Inverse potential scaling in co-electrocatalytic activity for CO reduction through redox mediator tuning and catalyst design.

Electrocatalytic CO reduction is an attractive strategy to mitigate the continuous rise in atmospheric CO concentrations and generate value-added chemical products. A possible strategy to increase the activity of molecular systems for these reactions is the co-catalytic use of redox mediators (RMs), which direct reducing equivalents from the electrode surface to the active site. Recently, we demonstrated that a sulfone-based RM could trigger co-electrocatalytic CO reduction an inner-sphere mechanism under aprotic conditions.

Homogeneous Catalytic Reduction of O to HO by a Terpyridine-Based FeNO Complex.

We report a new terpyridine-based FeNO catalyst, Fe(tpypho)Cl, which reduces O to HO. Variable concentration and variable temperature spectrochemical studies with decamethylferrocene as a chemical reductant in acetonitrile solution enabled the elucidation of key reaction parameters for the catalytic reduction of O to HO by Fe(tpypho)Cl. These mechanistic studies suggest that a 2 + 2 mechanism is operative, where hydrogen peroxide is produced as a discrete intermediate, prior to further reduction to HO.

Bioinspired mononuclear Mn complexes for O activation and biologically relevant reactions.

A general interest in harnessing the oxidizing power of dioxygen (O) continues to motivate research efforts on bioinspired and biomimetic complexes to better understand how metalloenzymes mediate these reactions. The ubiquity of Fe- and Cu-based enzymes attracts significant attention and has resulted in many noteworthy developments for abiotic systems interested in direct O reduction and small molecule activation. However, despite the existence of Mn-based metalloenzymes with important O-dependent activity, there has been comparatively less focus on the development of these analogues relative to Fe- and Cu-systems.