Bipyridyl Complexes Research Articles

An Efficient Fluorescent Chemosensing Probe for Total Determination and Speciation of Ultra-Trace Levels of Mercury (II) Species in Water.

The current study reports a novel fluorescent chemosensor based on the tagging agent 4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein (Rose Bengal, RB) for detection of trace levels of Hg2+in environmental water. The established probe has been based upon liquid-liquid extraction (LLE) of the developed ternary complex ion associate {[Hg (bpy)2]2+.[RB]2-} of Hg2+ -2,2- bipyridyl complex [Hg (bpy)2]2+ and RB at pH 9.0 onto chloroform and measuring the resulting fluorescence enhancement signal intensity at λex/em = 570/ (580-600) nm. The limits of detection (LOD) and quantification (LOQ) of for Hg2+ was calculated to be 6.06 and 20 nM with a linear dynamic range (LDR) of 0.02-20µM, respectively. The stability constant, stoichiometry, chemical equilibria, and the thermodynamic parameters (ΔH, ΔS, and ΔG) of the developed ion associate were evaluated and assigned. Student's t and F tests at 95% confidence were fruitfully used for validation of the proposed methodology for Hg2+ detection in water samples with the aid of inductively coupled plasma-optical emission spectrometry (ICP-OES). The established strategy was successfully applied for detection of trace levels of Hg2+ in water samples with acceptable results. The proposed probe was satisfactorily applied for total determination and speciation of Hg in various water samples. Integrating the functional chelating agent onto associate formation to improve the selectivity and sensing properties of the LLE combining sensing probe towards target analyte in water represent the main interest.

Light exposure of tetra-cationic porphyrins containing peripheral Pd(II)-bipyridyl complexes and the induced effects on purified DNA molecule, fibroblast and melanoma cell lines.

Photodynamic therapy (PDT) combines a light source, oxygen, and a photosensitizer (PS) to generate reactive oxygen species (ROS) for treating diseases. In this study, we evaluated two meso-tetra-pyridyl porphyrins with [Pd(bpy)Cl]+, namely 3-PdTPyP and 4-PdTPyP, as PS for PDT application. DNA interaction was assessed by spectroscopic measurements (UV-Vis and fluorescence emission), viscosity analysis, and molecular docking simulations. The results indicate that Pd(II)-porphyrins do not intercalate into DNA, suggesting that the minor groove is the primary interaction site, mainly through van der Waals forces. These metalloporphyrins effectively induced nitrogenous bases oxidation, particularly in purines, after white light irradiation. The induced DNA lesions were able to inactivate plasmid DNA metabolism (DNA replication and transcription) in a bacterial model. 3-PdTPyP and 4-PdTPyP significantly decreased the viability of treated melanoma cell lines (A375 and B16-F10), demonstrating that melanoma cell lines were more sensitive to these Pd(II)-porphyrins than the fibroblast cell line (L929). Moreover, 3-PdTPyP was more photototoxic to A375 cells (IC50 = 0.43 μM), whereas 4-PdTPyP was more photototoxic to B16-F10 cells (IC50 = 0.51 μM). These findings suggest that these porphyrins are promising PS for future PDT research focused on skin cancer.

Guanidinate Yttrium Complexes Containing Bipyridyl and Bis(benzimidazolyl) Radicals.

Ancillary ligand scaffolds that sufficiently stabilize a metal ion to allow its coordination to an open-shell ligand are scarce, yet their development is essential for next-generation spin-based materials with topical applications in quantum information science. To this end, a synthetic challenge must be met: devising molecules that enable the binding of a redox-active ligand through facile displacement and clean removal of a weakly coordinating anion. Here, we probe the accessibility of unprecedented radical-containing rare-earth guanidinate complexes by combining our recently discovered yttrium tetraphenylborate complex [{(Me3Si)2NC(NiPr)2}2Y][(μ-η6-Ph)(BPh3)] with the redox-active ligands 2,2'-bipyridine (bpy) and 2,2'-bis(benzimidazole) (Bbim), respectively, under reductive conditions. Our endeavor resulted in the first evidence of guanidinate complexes that contain radicals, namely, a mononuclear bipyridyl radical complex, {(Me3Si)2NC(NiPr)2}2Y(bpy•) (1), and a dinuclear bis(benzimidazolyl) radical-bridged complex, [K(crypt-222)][{(Me3Si)2NC(NiPr)2}2Y]2(μ-Bbim•) (2'). The latter was achieved by an in situ reduction of [{(Me3Si)2NC(NiPr)2}2Y]2(μ-Bbim) (2), which was isolated from a salt metathesis reaction. 1 and 2 were characterized by X-ray crystallography and IR and UV-vis spectroscopy. Variable-temperature electron paramagnetic resonance spectroscopy was applied to gain insight into the distribution of unpaired spin density on 1 and 2'. Density functional theory calculations were conducted on 1 and 2' to elucidate further their electronic structures. The redox activity of 1 and 2' was also probed by electrochemical methods.

Structure Activity Relationships for Second‐Coordination Sphere Functional Group Dependent CO2 Reduction by Manganese Bipyridyl Electrocatalysts

AbstractA series of twelve second coordination sphere (SCS) functionalized manganese tricarbonyl bipyridyl complexes are investigated for their electrocatalytic CO2 reduction properties in acetonitrile. A qualitative and quantitative assessment of the SCS functional groups is discussed with respect to the catalysts’ thermodynamic and kinetic efficiencies, and their product selectivities. In probing a broad scope of functional groups, it is clear that only the aprotic ortho‐arylester SCS is capable of promoting the highly desired low‐overpotential proton‐transfer electron‐transfer (PT‐ET) pathway for selective CO production. The ortho‐phenolic analogues cause an increase in overpotential with a product selectivity favoring H2 evolution, consistent with a high‐overpotential pathway via the anionic [Mn−H]− intermediate. Alternative aprotic Lewis base functional groups such as trifluoromethyl, morpholine and acetamide are shown to also be capable of intermediate manganese hydride generation. The tertiary amine substituent, 2‐morpholinophenyl, exhibits a desirable product distribution characteristic of syn‐gas (CO : H2=30 : 48) with an impressive turnover frequency, while the secondary amine group, 2‐acetamidophenyl, induces a notable shift in selectivity with a faradaic yield of 55 % for the formate (HCO2−) product. In addition to their catalytic properties, cyclic voltammetry and infrared spectroelectrochemistry (IR‐SEC) studies are presented to probe pre‐catalyst electronic properties and the two‐electron reduction activation pathway.

An effective visible-light driven fumarate production from gaseous CO2 and pyruvate by the cationic zinc porphyrin-based photocatalytic system with dual biocatalysts.

Fumaric acid is a useful unsaturated dicarboxylic acid that serves as a precursor for the biodegradable plastics poly(butylene succinate) and poly(propylene fumarate). Currently, fumaric acid is mainly synthesised from petroleum resources such as benzene. It is therefore desirable to develop methods to produce fumaric acid from renewable resources such as those derived from biomass. In this work, an effective visible-light driven fumarate production from gaseous CO2 and pyruvate with the system consisting of triethanolamine, cationic water-soluble zinc porphyrin, zinc tetrakis(4-N,N,N-trimethylaminophenyl)porphyrin, pentamethylcyclopentadienyl coordinated rhodium(III) 2,2'-bipyridyl complex, NAD+, malate dehydrogenase (NAD+-dependent oxaloacetate-decarboxylating) and fumarase was developed.

Photoluminescent ruthenium(II) bipyridyl complexes containing phosphonium ylide ligands.

A P-ylide Ru(II) bipyridyl complex was readily synthetized and fully characterized, constituing one of the rare examples of photoluminescent metal ylide complexes. Its photophysical and redox properties have been compared with those of related NHC and cyclometalated Ru complexes and exploited in visible-light photocatalyzed SET and EnT processes.

Precise analyses of photoelectrochemical reactions on particulate Zn0.25Cd0.75Se photoanodes in nonaqueous electrolytes using Ru bipyridyl complexes as a probe.

Recombination of photoexcited carriers at interface states is generally believed to strongly govern the photoelectrochemical (PEC) performance of semiconductors in electrolytes. Sacrificial reagents (e.g., methanol or Na2SO3) are often used to assess the ideal PEC performance of photoanodes in cases of minimised interfacial recombination kinetics as well as accelerated surface reaction kinetics. However, varying the sacrificial reagents in the electrolyte means simultaneously changing the equilibrium potential and the number of electrons required to perform the sacrificial reaction, and thus the thermodynamic and kinetic aspects of the PEC reactions cannot be distinguished. In the present study, we propose an alternative methodology to experimentally evaluate the energy levels of interfacial recombination centres that can reduce PEC performance. We prepare nonaqueous electrolytes containing three different Ru complexes with different bipyridyl ligands; redox reactions of Ru complexes represent one-electron processes with similar charge transfer rates and diffusion coefficients. Therefore, the Ru complexes can serve as a probe to isolate and evaluate only the thermodynamic aspects of PEC reactions. Recombination centres at the interface between a nonaqueous electrolyte and a Zn0.25Cd0.75Se particulate photoanode are elucidated using this method as a model case. The energy level at which photocorrosion proceeds is also determined.

Enhanced Visible Light-Driven Photocatalytic Water-Splitting Reaction of Titanate Nanotubes Sensitised with Ru(II) Bipyridyl Complex.

The ion exchange of Na+ cations was used to photosensitise titanates nanotubes (Ti-NTs) with tris(2,2'-bipyridine)ruthenium(II) cations (Ru(bpy)32+); this yielded a light-sensitised Ti-NTs composite denoted as (Ru(bpy)3)Ti-NTs, exhibiting the characteristic absorption of Ru(bpy)32+ in visible light. Incident photon-to-current efficiency (IPCE) measurements and the photocatalytic reduction of methyl viologen reaction confirmed that in the photosensitisation of the (Ru(bpy)3)Ti-NTs composite, charge transfer and charge separation occur upon excitation by ultraviolet and visible light irradiation. The photocatalytic potential of titanate nanotubes was tested in the water-splitting reaction and the H2 evolution reaction using a sacrificial agent and showed photocatalytic activity under various light sources, including xenon-mercury lamp, simulated sunlight, and visible light. Notably, in the conditions of the H2 evolution reaction when (Ru(bpy)3)Ti-NTs were submitted to simulated sunlight, they exceeded the photocatalytic activity of pristine Ti-NTs and TiO2 by a factor of 3 and 3.5 times, respectively. Also, (Ru(bpy)3)Ti-NTs achieved the photocatalytic water-splitting reaction under simulated sunlight and visible light, producing, after 4 h, 199 and 282 μmol×H2×gcat-1. These results confirm the effective electron transfer of Ru(bpy)3 to titanate nanotubes. The stability of the photocatalyst was evaluated by a reuse test of four cycles of 24 h reactions without considerable loss of catalytic activity and crystallinity.

Heteroleptic/Heterometallic Sierpiński Triangle with Room Temperature Fluorescence Emission and Photocatalytic Amine Oxidation Activity.

As a result of their optical and redox properties, bipyridyl (bpy) and terpyridyl (tpy) ruthenium complexes play vital roles in numerous domains. Herein, the design and synthesis of two bipyridyl and terpyridyl ruthenium(II) building units L1 and L2 are explained. A [Ru(bpy)3]2+ functionalized triangle S1 and a Sierpiński triangle S2 were synthesized in almost quantitative yields by the self-assembly of L1 with Zn2+ ions and by the heteroleptic self-assembly of L1 and L2 with Zn2+ ions, respectively. The Sierpiński triangle S2 contains the coordination metals [Ru(bpy)3]2+, [Ru(tpy)2]2+, and [Zn(tpy)2]2+. According to research on the catalytic activity of amine oxidation on supramolecules S1 and S2, the benzylamine substrates were nearly entirely transformed to N-benzylidenebenzylamine derivatives after 1 h under a Xe lamp. Furthermore, the observed ruthenium-containing terpyridyl supramolecule S2 maintains high luminous performance at ambient temperature. This discovery opens up new possibilities for the rational molecular design of terpyridyl ruthenium fluorescent materials and catalytic functional materials.

Laser-induced graphene as a sustainable counter electrode for DSSC enabling flexible self-powered integrated harvesting and storage device for indoor application

Dye-sensitized solar cells (DSSCs) are gaining a newfound interest thanks to their superior ability to harvest indoor light with efficiency higher than other photovoltaic technologies. This study reports, for the first time, the possibility of using laser-induced graphene (LIG) as a flexible counter electrode material for DSSCs. A flexible LIG (F-LIG) electrode was fabricated by direct laser writing of a polyimide film, without the need of a starting conductive substrate. The prepared electrodes showed a higher catalytic activity towards the reduction of I3−/I−with respect to a more expensive Pt-based counter electrode. Moreover, the F-LIG electrodes outperformed electrodeposited PEDOT as a catalytic material for reduction of a copper bipyridyl complex (Cu(II/I)(tmby)2TFSI2/1) electrolyte. The F-LIG based DSSCs showed an open circuit voltage as high as 0.94 V and an increase in photoconversion efficiency higher than 60% with respect to the PEDOT-based counterpart, stepping from 3.08% to 4.96%. Thanks to the easy one-step laser-based fabrication process, the LIG-based DSSC was integrated with a LIG-based supercapacitor (SC), obtaining a flexible energy harvesting and storage system that was able to self-charge both under simulated solar illumination and under indoor artificial illumination, appearing to be a promising energy source for the next generation of self-powered connected Internet of Things devices.

A bipyridyl quinoline ruthenium(Ⅱ) complex as a “Light Switch” for living cell mitochondrial singlet oxygen

Visualization of 1O2 in cells is of great significance for revealing the laws of life activities. Although many 1O2 fluorescent probes have been reported, their mechanism of capturing 1O2 has not been innovated. Herein, we report a ruthenium(Ⅱ) bipyridyl complex [Ru(bpy)2L3]PF6 with the ability to specifically identify 1O2 based on a novel mechanism of action. The non-fluorescent [Ru(bpy)2L3]PF6 can be accurately oxidized by 1O2 to generate a fluorescent substance with a large Stokes shift (184 nm). [Ru(bpy)2L3]PF6 was successfully applied for visualizing the generation process of 1O2 in living cells and monitoring the morphological changes of mitochondria during photodamage. Therefore, [Ru(bpy)2L3]PF6 has potential to be a useful molecular probe for analyzing physiological processes related to 1O2 in organisms.

On the Nature of the Partial Covalent Bond between Noble Gas Elements and Noble Metal Atoms

This article provides a discussion on the nature of bonding between noble gases (Ng) and noble metals (M) from a quantum chemical perspective by investigating compounds such as NgMY (Y=CN, O, NO3, SO4, CO3), [NgM-(bipy)]+, NgMCCH, and MCCNgH complexes, where M=Cu, Ag, Au and Ng=Kr-Rn, with some complexes containing the lighter noble gas atoms as well. Despite having very low chemical reactivity, noble gases have been observed to form weak bonds with noble metals such as copper, gold, and silver. In this study, we explore the factors that contribute to this unusual bonding behavior, including the electronic structure of the atoms involved and the geometric configuration of the concerned fragments. We also investigate the metastable nature of the resulting complexes by studying the energetics of their possible dissociation and internal isomerization channels. The noble gas-binding ability of the bare metal cyanides are higher than most of their bromide counterparts, with CuCN and AgCN showing higher affinity than their chloride analogues as well. In contrast, the oxides seem to have lower binding power than their corresponding halides. In the oxide and the bipyridyl complexes, the Ng-binding ability follows the order Au > Cu > Ag. The dissociation energies calculated, considering the zero-point energy correction for possible dissociation channels, increase as we move down the noble gas group. The bond between the noble gases and the noble metals in the complexes are found to have comparable weightage of orbital and electrostatic interactions, suggestive of a partial covalent nature. The same is validated from the topological analysis of electron density.

Antimicrobial photodynamic in vitro inactivation of Enterococcus spp. and Staphylococcus spp. strains using tetra-cationic platinum(II) porphyrins

This manuscript presents the first report on antimicrobial photo-inactivation in vitro using tetra-cationic porphyrins with peripheral platinum(II) bipyridyl complexes against Gram-positive bacteria. Two isomeric tetra-cationic porphyrins (3TPyP and 4TPyP) were tested against clinically important bacterial species. The antimicrobial activity assays were performed at specific photosensitizer (PS) concentrations under dark and white-light LED irradiation conditions for 120 min. The porphyrin 3-PtTPyP was the most efficient PS against the bacteria tested, inhibiting bacterial growth in just 15 min and 30 min at low concentrations (3.75 and 0.45 µM). The minimal inhibitory concentration of the porphyrin increased in the presence of reactive oxygen species scavengers, indicating that singlet oxygen and radical species likely participated in the photo-oxidation mechanism. In addition, the checkerboard assay that tests the association of compounds, showed a synergistic effect, suggesting a potentiation of the antibacterial effect when porphyrin was tested in combination with ciprofloxacin and vancomycin. Thus, tetra-cationic porphyrins containing platinum(II) complexes are promising agents for microbial photo-inactivation as an alternative therapy against infections.

Interaction of the Bipyridyl Gold(III) Complex with Anions of Thiol-Containing Acids in Aqueous Solution

The equilibria of stepwise substitution Au(bipy)+ OH– = Au(bipy)ClOH+ + Cl– and Au(bipy)+ 2OH– = Au(bipy)+ 2Cl– in aqueous solution at T = 25°C and I = 0.2 M (NaCl), log β1 = 9.22, log β2 = 16.61 have been studied. For bipyridyl complexes Au(bipy)(X = Cl, OH) at pH 2.0 and 7.4, redox interactions with anions of thiol-containing acids (glutathione, cysteine, thiomalate) have been studied. In all cases, at the initial stage, a rapid reduction of gold(III) to gold(I) was observed with the simultaneous release of bipyridyl. A detailed analysis of UV spectra showed that the main products of gold(III) reduction are highly stable gold(I) thiolate complexes. The presence of further slower steps depends on the initial ratio of thiol to gold.

Preparation of spiroborate supramolecular and peapod polymers containing a photoluminescent ruthenium(ii) complex.

The immobilization of functional metal complexes onto polymer supports remains one of the most important research areas. In this study, we prepared spiroborate supramolecular and peapod polymers containing a cationic photoluminescent ruthenium(ii) complex. The supramolecular polymer was obtained by mixing spiroborate cyclic trimer bearing homoallyl group and a ruthenium(ii) tris(bipyridyl) complex, and was further converted into the corresponding peapod polymer by olefin metathesis polymerization. The structure of these polymers was determined by 1H NMR, dynamic light scattering, inductively coupled plasma-atomic emission spectroscopy, energy dispersive X-ray analyses, and atomic force microscopy. The absorption and emission behaviors of the ruthenium(ii) complex were almost the same for the free form and the supramolecular polymer in the mixed solvent of N,N-dimethylformamide and chloroform, although the emission intensity decreased when the chloroform portion was increased. On the other hand, the hypsochromism was observed upon the emission of the ruthenium(ii) complex in the peapod polymer, probably due to the rigidochromic effect of the tight encapsulation by the peapod structure.

Multi-Stimuli-Responsive Organo-Sulfonated Anil and Its Organic Complex

Sensing by molecules is an intriguing phenomenon that can lead to next-generation intelligent materials. Stimuli-responsive organic molecules or molecular complexes, although less reported, can open up new avenues and opportunities in the area of artificial intelligence and memory. Extending the scope of organo-sulfonated Anils as stimuli-responsive materials, we report hydrated sulfonated Anil 1 and its nonstoichiometric bipyridyl complex 1.BPY. The formation of new materials is well supported and further substantiated through the solid-state structural elucidation of 1. Thermal and crystallographic studies validate the presence of two lattice water molecules each in 1 and 1.BPY. Structural studies also indicate that 1 undergoes intramolecular proton transfer between sulfonate and imine groups and exists in the zwitterionic form. Both 1 and 1.BPY respond to external stimuli: temperature, solvent polarity, and ammonia vapor. The thermochromism in both forms is reversible and interestingly triggered by the breathing of lattice water, a rare phenomenon in organic materials, supported by Fourier-transform infrared (FT-IR), thermal, and diffraction studies. Compared with the transition temperature of 130 °C for 1, 1.BPY undergoes a color change at 65 °C, and their heated forms, 1-Heat and 1.BPY-Heat, in turn, can be used as humidity sensors. Both solid forms exhibit solvatochromism and show emission turn-on in nonprotic polar solvents, dimethyl sulfoxide (DMSO) and dimethylformamide (DMF). The incipience of emission of 1.BPY in highly polar solvents DMSO (φ = 12%) and DMF (φ = 46%), and its absence in the solvents of relatively lower polarity such as H2O and MeOH as well as in solid forms, may be attributed to aggregation-induced quenching, which is supported by the solubility and DLS studies of 1 and 1.BPY in the solvents. Very interestingly and to the best of our knowledge, molecular solids 1 and 1.BPY represent the first examples of organic materials that exhibit emission turn-on on exposure to fumes of a base. When exposed to the fumes of ammonia, 1 and 1.BPY undergo a color change from maroon and orange to yellow, respectively, and the 1.NH3 and 1.BPY-NH3 forms show a striking green emission, which may be attributed to proton transfer within the molecular systems most likely involving the excited-state intermolecular proton-transfer (ESIPT) pathway. The overall analyses of the results indicate that the molecular complex 1.BPY is a better material vis-à-vis its response time (thermochromism), intensity (solvatochromic), and fatigue (vapochromism) and substantiate the scope of the crystal-engineering principles in designing next-generation smart materials.

Steric and Lewis Basicity Influence of the Second Coordination Sphere on Electrocatalytic CO2 Reduction by Manganese Bipyridyl Complexes.

This study aims to provide a greater insight into the balance between steric (bpy vs (Ph)2bpy vs mes2bpy ligands) and Lewis basic ((Ph)2bpy vs (MeOPh)2bpy vs (MeSPh)2bpy ligands) influence on the efficiencies of the protonation-first vs reduction-first CO2 reduction mechanisms with [MnI(R2bpy)(CO)3(CH3CN)]+ precatalysts, and on their respective transition-state geometries/energies for rate-determining C-OH bond cleavage toward CO evolution. The presence of only modest steric bulk at the 6,6'-diphenyl-2,2'-bipyridyl ((Ph)2bpy) ligand has here allowed unique insight into the mechanism of catalyst activation and CO2 binding by navigating a perfect medium between the nonsterically encumbered bpy-based and the highly sterically encumbered mes2bpy-based precatalysts. Cyclic voltammetry conducted in CO2-saturated electrolyte for the (Ph)2bpy-based precatalyst [2-CH3CN]+ confirms that CO2 binding occurs at the two-electron-reduced activated catalyst [2]- in the absence of an excess proton source, in contrast to prior assumptions that all manganese catalysts require a strong acid for CO2 binding. This observation is supported by computed free energies of the parent-child reaction for [Mn-Mn]0 dimer formation, where increased steric hindrance relative to the bpy-based precatalyst correlates with favorable CO2 binding. A critical balance must be adhered to, however, as the absence of steric bulk in the bpy-based precatalyst [1-CH3CN]+ maintains a lower overpotential than [2-CH3CN]+ at the protonation-first pathway with comparable kinetic performance, whereas an ∼2-fold greater TOFmax is observed at its reduction-first pathway with an almost identical overpotential as [2-CH3CN]+. Notably, excessive steric bulk in the mes2bpy-based precatalyst [3-CH3CN]+ results in increased activation free energies of the C-OH bond cleavage transition states for both the protonation-first and the reduction-first pathways relative to both [1-CH3CN]+ and [2-CH3CN]+. In fact, [3-CH3CN]+ requires a 1 V window beyond its onset potential to reach its peak catalytic current, which is in contrast to the narrower (<0.30 V) potential response window of the remaining catalysts here studied. Voltammetry recorded under 1 atm of CO2 with 2.8 M (5%) H2O establishes [2-CH3CN]+ to have the lowest overpotential (η = 0.75 V) in the series here studied, attributed to its ability to lie "on the fence" when providing sufficient steric bulk to hinder (but not prevent) [Mn-Mn]0 dimerization, while simultaneously having a limited steric impact on the free energy of activation for the rate-determining C-OH bond cleavage transition state. While the methoxyphenyl bpy-based precatalyst [4-CH3CN]+ possesses an increased steric presence relative to [2-CH3CN]+, this is offset by its capacity to stabilize the C-OH bond cleavage transition states of both the protonation-first and the reduction-first pathways by facilitating second coordination sphere H-bonding stabilization.

Microwave-assisted synthesis of pentamethylcyclopentadienyl iridium dihalide dimers

[Cp*IrCl2]2 is a common precursor used to synthesize a large family of organometallic catalysts. While [Cp*IrCl2]2 is commercially available, dimers featuring other halides are not, although they can be accessed through [Cp*IrCl2]2. Published synthetic methods for the preparation of these halide dimers are time consuming, requiring reflux for 48 h. We have developed a new synthetic approach utilizing microwave-assisted synthesis (MAS) that significantly decreases the time required to prepare [Cp*IrX2]2 (X = Cl, Br, I). Reagents were heated beyond their normal boiling point in sealed reactors for 15 min at 120 °C and products were isolated using traditional methods with yields comparable or exceeding literature methods. [Cp*IrX2]2 dimers synthesized using MAS were characterized by NMR spectroscopy, UV–Visible spectroscopy, and elemental analysis. These dimers were then used to synthesize a series of mononuclear iridium bipyridyl complexes, [Cp*Ir(bpy)X]X. This series of complexes was explored spectroscopically and electrochemically to identify potential electrocatalysts for future studies.

Role of the Trifluoropropynyl Ligand in Blue-Shifting Charge-Transfer States in Emissive Pt Diimine Complexes and an Investigation into the PMMA-Imposed Rigidoluminescence and Rigidochromism.

Square-planar PtII complexes are of interest as dopants for the emissive layer of organic light-emitting diodes. Herein, the photophysics of three Pt bipyridyl complexes with the strongly e- withdrawing, high-field, 3,3,3-trifluoropropynyl ligand has been investigated. One complex, (phbpy)PtC2CF3 (phbpy = 6-phenyl-2,2'-dipyridyl), has also been characterized by single-crystal X-ray diffraction. All complexes reported are emissive in both RT CH2Cl2 solution (ΦPL = 0.007 to 0.027) and PMMA film (ΦPL = 0.25 to 0.42). The trifluoropropynyl ligand elevates the energy of the MLCT and LL'CT states above that of the IL π-π* state, resulting in IL emission in all cases. The emission energies of the trifluoropropynyl compounds are also blue-shifted relative to the analogous pentafluorophenylethynyl compounds, suggesting that the trifluoropropynyl ligand is one of the most electron-withdrawing alkynyl ligands. Rate constants for radiative and nonradiative deactivation were determined from experimentally determined values of ΦPL and excited-state lifetimes in both solution and PMMA films. The increase in ΦPL upon incorporation into PMMA film (rigidoluminescence) results from a decrease in the rate constant for non-radiative relaxation. Experimental activation energies for excited-state decay in combination with TDDFT are consistent with the rigidoluminescence resulting from an increase in the energy of the non-emissive triplet metal-centered state. Two of the complexes investigated, (Ph2bpy)Pt(C2CF3)2 and (t-Bu2bpy)Pt(C2CF3)2, where t-Bu2bpy = 4,4'-di-tert-butyl-2,2'-dipyridyl and Ph2bpy = 4,4'-diphenyl-2,2'-dipyridyl, exhibit concentration-dependent excimer emission (orange) along with monomer emission (blue), enabling fine-tuning of the emission color. However, excimer emission was absent in cured PMMA films up to the solubility limit for solution processing of (Ph2bpy)Pt(C2CF3)2 in CH2Cl2, demonstrating the diffusional nature of excimer formation.

Highly Robust Rhenium(I) Bipyridyl Complexes Containing Dipyrromethene-BF2 Chromophores for Visible Light-Driven CO2 Reduction.

New rhenium bipyridyl complexes with dipyrromethene-BF2 chromophores (A-ReBDP-CZ, A-ReBDP2 , ReBDP-CZ, and ReBDP2 ) were developed for highly efficient photocatalytic carbon dioxide (CO2 ) reduction to carbon monoxide (CO). These catalysts consisted of two moderate electron-deficient groups (dipyrromethene-BF2 , BDP) as the visible-light-harvesting antenna as well as both electron donor (N-phenylcarbazole, CZ) and acceptor (BDP) on Re bipyridyl framework. Among ReBDP-CZ and ReBDP2 complexes, the ReBDP2 incorporating two electron-deficient BDP chromophores had a longer-lived photoexcited state (182.4 μs) and a twofold enhanced molar absorption coefficient (ϵ=157000 m-1 cm-1 ) compared with ReBDP-CZ. Thus, ReBDP2 achieved the superior photocatalytic reactivity and stability with a CO turnover number (TONCO ) value as high as 1323 and quantum yield (ΦCO ) up to 55 %, which was the most excellent photocatalysis efficiency among the single-active-site Re catalysts without additional photosensitizer. Furthermore, the acetylene-bridged linker was detrimental to the photoactivity and durability of the catalyst. In brief, two BDP-based Re bipyridyl systems with outstanding catalytic performance and significant visible-light-harvesting capabilities in the solar spectrum offer a promising strategy for solar-to-fuel conversion schemes.