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Herein we report a ligand-centered redox-controlled strategy for the synthesis of an unusual binuclear diradical cobalt(III) complex, [Co2 III(L•3–)2] (1), featuring two three-electron reduced trianionic monoradical 2,9-bis(phenyldiazo)-1,10-phenanthroline ligands (L •3–) and two intermediate-spin cobalt(III) centers having a Co–Co bond. Controlled ligand-centered oxidation of 1 afforded two mononuclear complexes, [CoII(L •–)(L0)]+ ([3])+ and [CoII(L0)2]2+ ([2]2+), which upon further ligand-centered reduction yielded a di-azo-anion diradical complex, [CoII(L •–)2] (4). In complex 1, two three-electron reduced di-azo-anion monoradical ligands (L •3–) bridge two intermediate Co(III) centers at a distance of 2.387(2) Å, while upon oxidation, one of the coordinating azo-arms of L becomes pendent, and in complexes [2]2+, [3]+, and 4, two tetradentate ligands coordinate a single Co(II) center in a tridentate meridional fashion with one uncoordinated azo-arm from each of the ligands. In the presence of reducing agents, the monomers [2]2+, [3]+, and 4 undergo ligand-centered reduction to form azo-anion radicals, and the otherwise pendent azo-arms in the presence of cobalt(II)-salts like Co(ClO4)2 or CoCl2 bind the second Co(II)-ion; further internal electron transfer from the cobalt center to the arylazo backbone produces the binuclear complex 1. Spectroscopic analysis, DFT studies, and control experiments were performed to understand the electronic structures and the ligand-centered redox-controlled interconversion. The application of complex 1 as a molecular memory device (memristor) was also explored. Complex 1 showed encouraging results as a memristor with a current ON/OFF ratio > 104 and is highly promising for resistive RAM/ROM applications.

devices has surged from 3.8% to 25.5%. [2] Furthermore, perovskites also exhibit fascinating properties, such as easy solution processing, bandgap tunability, narrow band absorption as well as emission, high quantum yield, long carrier diffusion length as well as lifetime, excellent carrier transport, and so on. [3] Despite these exciting features, the commercialization of lead-based perovskites encounters enormous challenges due to their poor stability in ambient condition and lead toxicity to the environment. Therefore, the search for nontoxic alternatives of lead (Pb) has recently become one of the most critical research directions in perovskites.The advancement to develop lead-free or lead-less perovskite materials is still far from satisfactory since the replacement of Pb often worsens the remarkable optoelectronic properties. For example, isovalent substitution of Pb 2+ by atoms like Sn 2+ and Ge 2+ negatively impacts the photovoltaic properties of the material due to rapid conversion to higher oxidation state to Sn 4+ and Ge 4+ , respectively. [4] Alternatively, heterovalent substitution (M(III) = Sb 3+ , Bi 3+ , Au 3+ , In 3+ , etc.) was also implemented to obtain Cs 3 M(III) 2 X 9 (X = Br, Cl, or I) 2D layered perovskite derivatives. [5] However, these materials generally depict poor properties, including low carrier mobility, indirect bandgap, and large optical gap for direct bandgap since the layers of corner connected M(III)-centered octahedral are separated by layers of cationic vacancies. [6] To overcome these complications, Vargas et al. first introduced 〈111〉-oriented vacancy-ordered cesium copper antimony chloride [Cs 4 Cu(II)Sb(III) 2 Cl 12 or CCAC] layered double perovskite structure in 2017, which shows a direct bandgap of 1.0 eV. [7] Interestingly, this material does not decompose even in the presence of high humidity and upon exposure to light unlike lead halide perovskite. Further, Singhal et al. reported an easy mechanochemical growth of CCAC with long-range magnetic ordering due to the presence of an unpaired electron through Cu II -d 9 electrons. [8] Bulk CCAC perovskite has low carrier mobility due to high electron effective mass, thus hindering further device application. [9] Brain-inspired artificial neural networks and neuromorphic computing are taking space to a new height based on solid-state memristor devices. Despite considerable progress already made, the use of lead-free double perovskite materials with direct bandgap can be recognized as a significant paradigm shift in this field. Here, growth, thin film deposition, and analog electroforming-free resistive switching property along with promising artificial synaptic and neural activities of lead-free layered cesium copper antimony chloride (Cs 4 CuSb 2 Cl 12 or CCAC) double perovskite nanocrystals are reported. Optical and structural characterizations of CCAC microcrystals (MCs) and nanocrystals (NCs) confirm the growth, the existence of direct bandgap, and <111> oriented monoclinic crystal phase of space group C2/m. Inte...

Here, we report robust and highly reproducible nonvolatile resistive switching (RS) devices with artificial synaptic functionalities utilizing redox-exfoliated few-layered 2H-MoS 2 nanoflakes. Advantageous polar solvent compatibility of 2D MoS 2 from this method were utilized to fabricate thin film devices very easily and cost-effectively using polystyrene as matrix. Prominent RS property of polystyrene thin film devices with varying MoS 2 concentrations strongly favors electroforming-free operation. The conduction band position of 2D MoS 2 nanosheet in combination with the work functions of chosen electrodes looks alleviating to switch the current from low to high at a suitable positive bias voltage. We further confirmed the mechanism of charge transport through fitting the results with theoretical models, say injectiondominated Schottky emission model for low-conducting states and space-charge-limited current mechanism for the high-conducting state. Interestingly, a relatively high current On/Off ratio 10 2 was recorded during the pump-probe testing to show resistive random-access memory (ReRAM) application. Finally, artificial synaptic functionalities-the building blocks of neuromorphic computing architectures is also illustrated by considering the robust RS property and ReRAM application.

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