Synthesis, Study, and Application of Pd(II) Hydrazone Complexes as the Emissive Components of Single-Layer Light-Emitting Electrochemical Cells

Full Solution Process of a Near-Infrared Light-Emitting Electrochemical Cell Based on Novel Emissive Ruthenium Complexes of 1,10-Phenanthroline-Derived Ligands and a Eutectic Alloy as the Top Electrode

Near-infrared luminescent materials have recently received considerable attention for a large number of applications, including in solid-state lighting, as bioimaging agents, as photovoltaic cells, and in the telecommunication industry. By adding diverse electron-donating or withdrawing groups on ancillary ligands based on benzenethiol-phenanthroline, we synthesized and optoelectronically characterized a series of novel ionic ruthenium complexes, namely RuS, RuSCl, RuSMe, and RuSNH₂, for using in a light-emitting electrochemical cell. The synthesized complexes are intense red emitters in the range of 584-605 nm in solution, which depends on the substitutions of electron donor/acceptor moieties on the ancillary ligands. To find a suitable quantum mechanical approach, benchmark calculations based on time-dependent density functional theory were carried out on these complexes. Our benchmark revealed that the M06-L method has results close to those of the experiment. Furthermore, to gain a deeper insight into electronic transitions, several excitation processes were investigated at the TD-DFT-SMD-MN12-L/gen level. The results showed that in the designed complexes, the dominant transition is between the 4d_Z² electron of Ru (particle) and the π* orbitals of the ancillary ligand (hole). The single-layer devices, including these complexes along with a Ga/In cathode by a facile deposition method without the addition of any electron or hole transport layers, were fabricated and displayed red (678 nm) to near-infrared (701 nm) emission as well as a decrease of turn-on voltage from 3.85 to 3.10 V. In particular, adding a methyl group to the ancillary ligand in the complex RuSNH₂ increases the external quantum efficiency to 0.55%, one of the highest observed values in the ruthenium phenanthroline family. This simple structure of the device lets us develop the practical applications of light-emitting electrochemical cells based on injection and screen-printing methods, which are very promising for the vacuum-free deposition of top electrodes.

Investigation of electrocatalytic activity of a new mononuclear Mn(II) complex for water oxidation in alkaline media

Water splitting is a promising way to alleviate the energy crisis. In nature, water oxidation is done by a tetranuclear manganese cluster in photosystem II. Therefore, the study of water oxidation by Mn complexes is attractive in water splitting systems. In this report, a new mononuclear Mn(II) complex, MnL₂ (HL = (E)-3-hydroxy-N'-(pyridin-2-ylmethylene)-2-naphthohydrazide) was prepared and characterized by spectroscopic techniques and single-crystal X-ray diffraction. Crystallographic analysis indicated that the geometry around the Mn(II) ion is distorted octahedral. The MnN₄O₂ coordination moiety is achieved by bounding of oxygen and two nitrogen donor atoms of two hydrazone ligands. The synthesized complex was also investigated for electrochemical water oxidation using electrochemical techniques, scanning electron microscopy, energy dispersive spectrometry, and PXRD analysis. Linear sweep voltammetry experiment showed that the modified carbon paste electrode by the complex displays high activity for water oxidation reaction with an overpotential of 565 mV at a current density of 10 mA cm^-2 and Tafel slope of 105 mV dec^-1 in an alkaline solution. It was found that the complex structure finally changes during the reaction and converts to Mn oxide nanoparticles which act as active catalytic species and oxidize the water.

Green solvent free epoxidation of olefins by a heterogenised hydrazone-dioxidotungsten(vi) coordination compound

A new mononuclear tungsten coordination compound, [WO₂L(CH₃OH)] (1), was synthesized by the reaction of WCl₆ and H₂L (H₂L = (E)-4-amino-N′-(5-bromo-2-hydroxybenzylidene)benzohydrazide) in methanol. Both the H₂L and compound 1 were characterized by elemental analysis and UV-Vis, FT-IR and NMR spectroscopic methods. The molecular structure of compound 1 was also determined by single crystal X-ray analysis which confirmed the compound is a mononuclear coordination compound of cis-dioxidotungsten(vi) containing a free amine functionality on the ligand. Compound 1 was supported on propionyl chloride-functionalized silica gel by amidification reaction to obtain a heterogeneous catalyst. The obtained heterogeneous catalyst was characterized by FT-IR spectroscopy, thermal gravimetric analysis (TGA), diffuse-reflectance spectroscopy (DRS), X-ray diffraction analysis (XRD), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) and its catalytic activity was investigated in the epoxidation of olefins with hydrogen peroxide under solvent free conditions. The catalyst was successfully recovered several times and the recovered catalyst was also characterized by various methods including FT-IR, DRS, TGA, SEM and EDX analyses. The results indicated this heterogeneous catalytic system is an effective and selective catalyst for epoxidation of olefins and can be reused several times without significant change in its catalytic activity.

In this study the solvent free catalytic oxidation of olefins by a new silica supported hydrazone-dioxidotungsten(vi) coordination compound is investigated.

High-Efficiency Deep-Red Light-Emitting Electrochemical Cell Based on a Trinuclear Ruthenium(II)-Silver(I) Complex

Turn-on time is a key factor for lighting devices to be of practical application. To decrease the turn-on time value of a deep-red light-emitting electrochemical cells (DR-LECs), two novel approaches based on molecularly engineered ruthenium phenanthroimidazole complexes were introduced. First, we found that with the incorporation of ionic methylpyridinium group to phenanthroimidazole ligand, the turn-on time of the DR-LECs device was dramatically reduced, from 79 to 27 s. By complexation of ruthenium emitter with Ag⁺, the turn-on time was improved by 85%, and the EQE of DR-device was increased from 0.62 to 0.71%. These results open a new avenue in decreasing the turn-on time without adding ionic electrolytes, leading to an efficient LEC.

Zinc (II) and AIEgens: The "Clip Approach" for a Novel Fluorophore Family. A Review

Aggregation-induced emission (AIE) compounds display a photophysical phenomenon in which the aggregate state exhibits stronger emission than the isolated units. The common term of "AIEgens" was coined to describe compounds undergoing the AIE effect. Due to the recent interest in AIEgens, the search for novel hybrid organic-inorganic compounds with unique luminescence properties in the aggregate phase is a relevant goal. In this perspective, the abundant, inexpensive, and nontoxic d10 zinc cation offers unique opportunities for building AIE active fluorophores, sensing probes, and bioimaging tools. Considering the novelty of the topic, relevant examples collected in the last 5 years (2016-2021) through scientific production can be considered fully representative of the state-of-the-art. Starting from the simple phenomenological approach and considering different typological and chemical units and structures, we focused on zinc-based AIEgens offering synthetic novelty, research completeness, and relevant applications. A special section was devoted to Zn(II)-based AIEgens for living cell imaging as the novel technological frontier in biology and medicine.