Ligand Charge Transfer Research Articles

Luminescent Iridium-Terpyridine Complexes with Various Bis-Cyclometalated Ligands.

A series of luminescent bis-cyclometalated iridium complexes with 2,2':6',2″-terpyridine (tpy), [Ir(C^N)2(tpy)]PF6 (C^N = 2-phenylpyridinate (ppy) for 1; benzo[h]quinolinate (bzq) for 2; 1-phenylisoquinolinate (piq) for 3; and 2-phenylbenzothiazolate (pbt) for 4), have been synthesized and structurally characterized. Single-crystal X-ray diffraction analyses reveal that the tpy ligands of 1-4 are coordinated to the iridium center in a bidentate fashion, and the uncoordinated pendant pyridine rings in the tpy ligands of 1-4 form intramolecular π-π stacking interactions with a phenyl moiety of C^N ligands. In addition, the pendant pyridine ring in the tpy ligand of 1 forms an intramolecular hydrogen bonding interaction, unlike in 2-4. Of interest, the photophysical properties of 1-4 are strongly influenced by the C^N ligands; 1 shows a luminescence band at 572 nm, with a short lifetime (τ) value of 80 nsec and a lower absolute luminescence quantum yield (Φ) of 3.72%, whereas 3 exhibits an intense luminescence band at 588 nm with a long τ value of 1965 nsec and a moderate Φ value of 9.57%. The density functional theory calculations revealed that the luminescence originates from the triplet metal-ligand to ligand charge transfer (3MLL'CT) excited state.

Visible Light Photolysis at Single Atom Sites in Semiconductor Perovskite Oxides.

Designing catalysts with well-defined active sites with chemical functionality responsive to visible light has significant potential for overcoming scaling relations limiting chemical reactions over heterogeneous catalyst surfaces. Visible light can be leveraged to facilitate the removal of strongly bound species from well-defined single cationic sites (Rh) under mild conditions (323 K) when they are incorporated within a photoactive perovskite oxide (Rh-doped SrTiO3). CO, a key intermediate in many chemistries, forms stable geminal dicarbonyl Rh complexes (Rh+(CO)2), that could act as site blockers or poisons during a catalytic cycle. For the first time, we demonstrate that CO removal can occur at mild temperatures (323 K) under low-energy red light (635 nm) irradiation, which is not possible for supported isolated-site Rh catalysts (0.2 wt % Rh/γ-Al2O3). Photolysis of supported Rh+(CO)2 complexes (e.g., 0.2 wt % Rh/γ-Al2O3) has been demonstrated but is limited to high energy UV photons. Rigorous kinetic experiments elucidate disparate mechanisms for CO photodepletion from Rh-doped SrTiO3 and supported isolated site Rh/γ-Al2O3. CO photodepletion from supported isolated site Rh/γ-Al2O3 involves a direct metal to ligand charge transfer mechanism, whereas Rh-doped SrTiO3 is governed by electron-hole pair formation in the perovskite. We show that under visible, low-energy red light, surface Rh species in Rh-doped SrTiO3 introduce midgap energy states above the valence band that facilitate electronic excitations leading to surface CO removal. Isolated Rh sites in Rh-doped SrTiO3 also exhibit exceptional stability under multiple CO photodepletion cycles. Overall, incorporating single sites into photoactive perovskite oxides is an effective strategy to influence surface chemistries with visible light.

Single-Component Coordination Polymers with Excitation Wavelength- and Temperature-Dependent Long Persistent Luminescence toward Multilevel Information Security.

Metal-organic hybrid materials with long persistent luminescence (LPL) properties have attracted a lot of attention due to their enormous potential for applications in information encryption, anticounterfeiting, and other correlation fields. However, achieving multimodal luminescence in a single component remains a significant challenge. Herein, we report two two-dimensional LPL coordination polymers: {[Zn2(BA)2(BIMB)2]·2H2O}n (1) and {[Cd(BA)(BIMB)]·3H2O}n (2) (BIMB = 1,3-bis(imidazol-1-yl)benzene; BA = butanedioic acid). Their LPL colors can be adjusted by the excitation wavelength or temperature variation in a single-component coordination polymer, achieving multimode color adjustment from green to orange or blue to yellow. X-ray single-crystal diffraction analysis and theoretical calculations demonstrate that abundant intermolecular interactions, ligand-to-ligand charge transfer (LLCT) transitions, and heavy atom effects of the central metal can realize multicolor afterglow. This work provides a convenient strategy for new pattern multicolor LPL materials and may also inspire new ideas for advanced information encryption technologies.

Diiridium(III) Complexes with Fluorenylpyridyl Cyclometalating and μ2‐Oxamidato Bridging Ligands and their High Efficiency Phosphorescent Solution‐Processed OLEDs

Three neutral diiridium(III) complexes with 2‐fluorenylpyridyl (flpy) or 5‐fluoro‐2‐fluorenylpyridyl (flpyF) as C^N cyclometalating ligands and a μ2‐oxamidato bridge have been synthesized. NMR spectroscopy shows that the complexes are inseparable mixtures of diastereomers (rac, DD/LL and meso, DL) with bridges in anti and syn configurations. Each isomer was determined using 19F NMR data on the flpyF complex. Single crystal diffraction studies of two complexes revealed meso diastereomers with anti configuration of the bis‐(t‐butylphenyl)oxamidato bridge but an uncertain configuration of the unsubstituted μ2‐oxamidato bridge. The complexes are highly emissive (ΦPL 57‐82% in solution) with excited state lifetimes of tp ca. 40 ms. The vibronic emissions with maxima at 553‐561 nm and at 587‐595 nm in solution are attributed to mixed metal‐ligand to ligand charge transfer (3MLLCT). Density functional theory (DFT) and time dependent‐DFT (TD‐DFT) calculations establish the involvement of the fluorenyl groups and the vibronic structures in the emissions. The bridge mediates intramolecular interactions between iridium centers based on electrochemical measurements Phosphorescent organic light‐emitting diodes (PhOLEDs) using these complexes as the emissive dopants with a solution‐processed active layer have bright greenish‐yellow emission with lmaxEL ca. 560 nm, luminous efficiency up to 26 cd/A and high external quantum efficiency (maximum hext ca. 20%).

Ligand Field and Charge Transfer in Transition-Metal Compounds

Ligand Field and Charge Transfer in Transition-Metal Compounds

Redox Reactions of [RuIII(pic)3] (pic−=picolinate) with Sulfite in Aqueous Solution: Kinetic, and Mechanistic Studies

AbstractThe reaction of [RuIII(pic)3] (pic−=picolinate) and sulfite (SO32−) resulting in the formation of [RuII(pic)3] − and sulfate (SO42−) has been studied spectrophotometrically and kinetically in aqueous solution. The rate of the reaction studied by following the appearance of the MLCT (metal to ligand charge transfer) band of the [RuII(pic)3)]− complex at 466 nm was found to be first‐order in both the complex and sulfite concentrations. The values of the observed rate constant depend on the pH, since it controls the speciation of oxoanions of sulfur(IV)‐species viz. bisulfite (HSO3−) and sulfite (SO32−) in the pH range 3.8 to 8.3. The product of the reaction, sulfate was ascertained by LDI‐mass spectral analysis ofthe post‐reaction solution. The activation parameters (ΔH≠ =56±3 kJ mol−1 and ΔS≠= ‐179±9 J mol−1 K−1) corresponding to the reduction of [RuIII(pic)3] with SO32− supports the operation of an outer‐sphere electron transfer mechanism. The experimentally observed electron‐transfer rate constant (k=5.60 M−1s−1 at 25 °C) is found to be in good agreement with that of calculated (k12=4.75 M−1s−1) using Marcus cross‐reaction relationship for outer‐sphere electron‐transfer reactions. A working mechanism consistent with the spectral and kinetic data is proposed for the aforesaid electron transfer reaction.

Blue Thermally Activated Delayed Fluorescent OLEDs With EQE up to 25% via 3MMLCT‐Induced and Short‐Lived Phosphorescent Dinuclear Pt(II) Sensitizers

AbstractThe novel dinuclear Pt(II) complexes, Di‐Pt‐CH3 and Di‐Pt‐CD3 with non‐fluorinated n‐hetero cyclic (NHC) ligands are developed. They exhibit phosphorescent emission in the range of 440–460 nm in film state with ≈60% photoluminescence quantum yield (PLQY) and a shorter lifetime due to a moderate Pt‐Pt distance of 3.21 Å. By suitably combining with blue multiresornance thermally activated delay fluorescence ( MR‐TADF) emitters, t‐DABNA and ν‐DABNA, efficient energy transfer is achieved from the triplet intraligand state (3IL) and triplet metal ligand change transfer (3MLCT) mixed states of Pt(II) complexes to the singlet state of the emitters. Importantly, the delayed triplet lifetime of the TADF emitter is shortened through the fast relaxation of triplet metal‐metal to ligand charge transfer (3MMLCT) states, possessing 0.07 eV lower energy compared to the triplet states of the TADF emitters. Di‐Pt‐CH3 and Di‐Pt‐CD3 are employed in phosphorescent and phosphorescent sensitized TADF (PS‐TADF) blue OLEDs, resulting in high external quantum efficiency (EQE) of 18.8% and 25.4%, respectively. An extremely low roll‐off characteristic of 9.8% is observed in the PS‐TADF OLED. Additionally, deuterium substitution of the methyl group improved phosphorescent device lifetime by 2.6 times. Notably, Di‐Pt‐CD3 resulted in significant lifetime enhancements: 4.7 times in phosphorescent devices and 6.6 times in PS‐TADF devices, compared with Ir(cb)3‐based devices. The mechanism for the increased lifetime is extensively studied through the magneto‐electroluminescence (MEL) and transient electroluminescence (TrEL) measurements.

Hydrothermally synthesized cobalt oxide/polydimethylsiloxane based photothermal absorber for superior thermal energy conversion and water evaporation application

Solar-driven interfacial evaporation has garnered worldwide interest in recent years due to its unique vapor generating capacity using sustainable solar energy. Many photoabsorber have been studied for conversion of photothermal energy and heat absorption. Unfortunately, the majority of the absorber materials in supply are pricey, and the installation procedures tend to be intricate. This research focuses on the ongoing difficulty of creating cost-efficient photothermal materials that have excellent light absorption and simple manufacturing processes. We created a novel composites coated with Cobalt oxide and polydimethylsiloxane (Co3O4/PDMS) which successfully produce energy and purify water utilizing an extensive spectrum of solar energy. Hydrothermally synthesized Co3O4 particles exhibit distinct optical properties in the UV–Vis region due to ligand field transitions and charge transfer between Co2⁺ and Co³⁺ ions. Additionally, these particles exhibits a strong absorption in the NIR region due to the intervalence charge transfer and d-d transitions, enhancing their photothermal activity. This culminates in outstanding light-to-heat transformation in the Co3O4/PDMS composite, which maintains a surface temperature of 42.7 °C compared to 33.7 °C for pristine PDMS under standard 1 sun intensity for 5 min. The flexible Co3O4/PDMS composite transfers solar energy to electric energy, producing ∼99 mV with 1 sun irradiation, while bare PDMS only achieved a voltage of 61 mV under 1 sun circumstances. An efficient double layer Co3O4/PDMS@MF sponge achieved an evaporation rate of 1.33 kg m−2 h−1 with the photothermal conversion efficiency of 68.8 %. These results motivate thorough investigation in photothermal potential of Co3O4, revealing the promising possibilities for harnessing solar-thermal energy and presents a novel method for using solar power to purify water and generate electricity.

Benzo[1,2-b:4,5-b’]dithiophene diethynyl bridged bimetallic ruthenium complexes: syntheses and characterization, (spectro)electrochemistry combined with theoretical calculations

We have constructed isomeric triruthenium ethynyl complexes 1 and 2 linked by benzo[1,2-b:4,5-b’]dithiophene. The electronic properties of 1 and 2 were compared by (spectro)electrochemical and theoretical calculations. DFT (density functional theory) fully-optimized structures 1 and 2 showed that the ruthenium terminal groups both exhibit a similar pseudo-octahedral configuration as reported for the crystal structure of 1. With step-by-step oxidation, the bond length of Ru-C decreases and the bond length of C≡C increases, which indicated that the complexes undergo a transition from Ru-C≡C to Ru = C = C. The electrochemical results of 1 and 2 featured two consecutive single-electron redox processes, and the ΔE value of 2 (329 mV) was significantly higher than that of 1 (140 mV). The near-IR broad absorptions of 2 + from UV-Vis-NIR spectroelectrochemistry exhibited a blue shift relative to that of 1 +, which could be attributed to MLCT (metal to ligand charge transfer) absorptions and confirmed by TDDFT (time dependent) calculations. The results suggested that the bridge ligands are involved in the redox process. The ν(C≡C) stretch of 2 + from IR spectroelectrochemistry exhibited a strong single peak at 1969 cm-1, while the isomer 1 + showed three asymmetric peaks. These results showed excellent charge delocalization ability of 2.

A homochiral Nickel(II) complex [Ni(P'N)2]Cl2: Synthesis, characterization, crystal structure, luminescence, DFT and Hirshfeld surface studies

A new complex ([Ni(P'N)2]Cl2) is synthesized from an anhydrous NiCl2 and a bidentate P'N (S,S)-NH2CHPhCHPhPPh2) ligand with an enantiopure ethylene backbone. The solubility of the complex in methanol aids its crystallization by slow evaporation. A single crystal X-ray diffraction study of the complex reveals a distorted square planar geometry with the phosphinyl groups coordinated in a cis(P,P) configuration. This imposes steric effects that influence the crystal packing of the complex in an orthorhombic unit cell. The complex possesses characteristic metal to ligand charge transfer (MLCT) transition in the UV region with a peak absorption at 294 nm corresponding to 4.22 eV, which correlates with 4.24 eV derived from the DFT calculation of the energy band gap between the highest molecular orbital (HOMO:7.39 eV) and lowest unoccupied molecular orbital (LUMO:3.15 eV) of the complex. With an excitation wavelength of 415 nm (3.00 eV), the complex emits photons with wavelength 488 nm (2.54 eV) in the blue region of the visible spectrum. The circular dichroism spectrum has multiple peaks in the UV region mainly associated with transitions within the chiral array of phenyl groups. The bond lengths, bond angles, and vibrational bands obtained by simulation of the optimized structure of the complex provide analytical details that strongly correlate with the experimental data with adjusted R2 of 0.9826 (bond lengths), 0.9911 (bond angles) and 0.9983 (vibrational bands). The Hirshfeld surface analysis shows that H…H and C…H interactions between phenyl rings of the cations contribute significantly to the crystal packing of the complex.

Prediction by DFT and Docking Calculations of a Series of Hypothetical 3d Transition Element Isostructural Complexes [M(hfac)2(TTF)2]: A Comparative Study

AbstractThe study aims to predict and compare the structural, electronic, conductivity, and biological properties of a series of 3d transition element complexes with those of the previously studied isostructural copper complex [Cu(hfac)2(TTF)2][PF6]2 (TTF: tetrathiafulvalene, hfac: hexafluoroacetylacetonate). Because transition metals hold open electronic shells, all possible spin states for all divalent compounds have to be considered in order to determine the most stable configurations. These configurations are those corresponding to the highest spin state (5 for Mn, 4 for Fe, 3 for Co, 2 for Ni, 1 for Cu, and 0 for Zn). However, the configurations with the smallest gap are Mn(3) and Co(1), suggesting that these are the most conductive complexes. A significant metal–ligand charge transfer is observed for both Mn and Co complexes. Antifungal (CYP121 (PDB: 2IJ7) and CYP51 (PDB: 1EA1)) and antibacterial (Escherichia coli (PDB: 1KZN)) properties of the compounds studied were evaluated by molecular docking; the results obtained reveal that the following complexes show significant activity: Zn(hfac)2(TTF)2] [PF6]2 (−8.9 kcal/mol), Ni(hfac)2(TTF)2] [PF6]2 (−7.8 kcal/mol), and Cu(hfac)2(TTF)2] [PF6]2 (−8.2 kcal/mol).

Novel CoFe2O4 / LaAlO3 nanocomposites: An impressive photocatalyst with p-n hetero-junction for improved H2 generation under visible exposure

The present work is devoted to the synthesis of perovskite LaAlO3 by Sol-Gel approach and its application for the photo-evolution of H2 in conjunction with cobalt ferrite CoFe2O4 prepared by nitrate route. The thermal analysis (TG/DSC) showed that the formation is completed at 600 °C. The X-ray diffraction (XRD) pattern is characteristic of a single phase, crystallizing in a rhombohedral symmetry with a crystallite size of 36 nm. The SEM micrographs revealed a homogeneous structure with an agglomeration of shaped grains (40–80 nm). The forbidden band (3.39 eV), calculated from diffuse reflectance data, is assigned to the ligand charge transfer O2−: 2p → Al3+: 3s orbital. As prepared, LaAlO3 is an n-type semiconductor as demonstrated from the capacitance - potential (C−2 - E) graph with an electron density of 9.4 × 1014 cm−3 due to oxygen under-stoichiometry. Attention was directed to photo-electrochemistry in connection with water reduction into hydrogen. With a negative conduction band potential (−0.11 VSCE), H2 generation can be synergized over the hetero-system by visible light. The photocatalytic capability of CoFe2O4 25%/LaAlO3 revealed a high H2 generation of 963 μmol g−1 in the alkaline electrolyte (NaOH, 0.1 M) with a catalyst dose of 1 mg mL−1, which is 1.3 times more than CoFe2O4 under similar conditions. Photoactivity is significantly improved by 60%, up to 2400 μmol g−1 in the presence of oxalate C2O42− as a hole scavenger in the hetero-junction, two hydrogen release tests were successfully recorded. The higher H2 production in the hetero-junction system is attributed to the lower recombination rate of electron/hole (e−/h+) in the material, due to the large band bending at the solid interfacial.

1,4-diaminophthalazine complexes of Re(CO)3

1,3-Diiminoisoindolines and substituted variants react with hydrazine to produce 1,4-diaminophthalazines. In this paper, we present the chemistry of 1,4-diaminophthalazine and two modified versions with the Re(CO)3 unit. The 1,4-diaminophthalazine ligand forms a bimetallic complex similar to that seen with unmodified phthalazine. In contrast, the semihemiporphyrazine-derived chelating ligands bind Re(CO)3 as neutral bidentate compounds; the freebase pyrazole and indazole modified 1,4-diaminophthalazines exhibit multiple tautomerization states with ionizable protons. Notably, protonation of the meso bridging nitrogen atom reduces the degree of conjugation between the two halves of the chelate, resulting in a diimine-like complex that lacks significant absorption in the visible spectrum due to the abrogation of the low energy metal to ligand charge transfer (MLCT) transition.

Two 2-dimensional Mn(II)-based coordination polymers: synthesis, structure and luminescence properties

Luminescent ligand 4-([4,2′:6′,4″-terpyridin]-4′-yl)-N,N-diphenylaniline (tpatpy) was coordinated to MnX2 (X = Cl, Br) to construct two novel coordination polymers (CPs) by two-solvent interdiffusion, delivering compounds 1 (C66H48Br2MnN8) and 2 (C66H48Cl2MnN8). Single-crystal X-ray diffraction revealed that the two CPs both possessed microstructures of 2-dimensional layers which were tuned by six-coordinate Mn2+ ions. Compounds 1 and 2 display broad photoluminescent emission with intense peaks at ca. 468 nm, attributed to π*→n or π*→π transitions mixed with the ligand-to-ligand charge transfer (LLCT) transition. Their crystal structures, powder diffraction (PXRD) and thermogravimetry (TG) are also discussed.

A new three-dimensional luminescent MOF for the detection of Fe3+, CrO42−, and Cr2O72− in aqueous solution

A new luminescent MOF were synthesized by solvothermal method based on 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethene (TPPE), with the molecular structure of [Zn2(TPPE)0.5(ndc)2]n (ndc = 1,4-Naphthalenedicarboxylic acid) (LMOF-1). The single crystal structure indicates that LMOF-1 stacks in a three-dimensional structure. The fluorescence test results indicate that LMOF-1 emits blue light with quantum yield at 37.93 %, due to ligand–ligand charge transfer. PXRD and TG analysis confirmed that LMOF-1 has good stability, and PXRD analysis after different solvent exchanges confirmed that LMOF-1 has good stability in water. The results of ion titration experiments show that Fe3+, CrO42−, and Cr2O72− have significant quenching effects on LMOF-1, and the detection limits are 3.83 × 10−6 M, 2.57 × 10−5 M, and 4.33 × 10−6 M, respectively. Indicating that LMOF-1 can serve as a multifunctional ion detector.

Sonoinduced Tumor Therapy and Metastasis Inhibition by a Ruthenium Complex with Dual Action: Superoxide Anion Sensitization and Ligand Fracture.

Photoresponsive ruthenium(II) complexes have recently emerged as a promising tool for synergistic photodynamic therapy and chemotherapy in oncology, as well as for antimicrobial applications. However, the limited penetration power of photons prevents the treatment of deep-seated lesions. In this study, we introduce a sonoresponsive ruthenium complex capable of generating superoxide anion (O2•-) via type I process and initiating a ligand fracture process upon ultrasound triggering. Attaching hydroxyflavone (HF) as an "electron reservoir" to the octahedral-polypyridyl-ruthenium complex resulted in decreased highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps and triplet-state metal to ligand charge transfer (3MLCT) state energy (0.89 eV). This modification enhanced the generation of O2•- under therapeutic ultrasound irradiation at a frequency of 1 MHz. The produced O2•- rapidly induced an intramolecular cascade reaction and HF ligand fracture. As a proof-of-concept, we engineered the Ru complex into a metallopolymer platform (PolyRuHF), which could be activated by low-power ultrasound (1.5 W cm-2, 1.0 MHz, 50% duty cycle) within a centimeter range of tissue. This activation led to O2•- generation and the release of cytotoxic ruthenium complexes. Consequently, PolyRuHF induced cellular apoptosis and ferroptosis by causing mitochondrial dysfunction and excessive toxic lipid peroxidation. Furthermore, PolyRuHF effectively inhibited subcutaneous and orthotopic breast tumors and prevented lung metastasis by downregulating metastasis-related proteins in mice. This study introduces the first sonoresponsive ruthenium complex for sonodynamic therapy/sonoactivated chemotherapy, offering new avenues for deep tumor treatment.

Efficient photoredox catalysis in C–C cross-coupling reactions by two-coordinated Au(I) complex

Photocatalysis provides a versatile approach to redox activation of various organic substrates for synthetic applications. To broaden the scope of photoredox catalysis, developing catalysts with strong oxidizing or reducing power in the excited state is imperative. Catalysts that feature highly cathodic oxidation potentials and long lifetimes in their excited states are particularly in demand. In this research, we demonstrate the catalytic utility of two-coordinate Au(I) complex photocatalysts that exhibit an exclusive ligand-to-ligand charge-transfer (LLCT) transition in C–C cross-coupling reactions between N-heterocycles and (hetero)aryl halides, including redox-resistant (hetero)aryl chlorides. Our photocatalysis system can steer reactions under visible-light irradiation at a catalyst loading as low as 0.1 mol% and exhibits a broad substrate scope with high chemo- and regioselectivity. Our mechanistic investigations provide direct spectroscopic evidence for each step in the catalysis cycle and demonstrate that the LLCT-active Au(I) complex catalysts offer several benefits, including strong visible-light absorption, a 210 ns-long excited-state lifetime without short-lived components, and a 91% yield in the production of free-radical intermediates. Given the wide structural versatility of the proposed catalysts, we envision that our research will provide useful insights into the future utilization of the LLCT-active Au(I) complex for organic transformations.

Phenanthroline-Mediated Photoelectrical Enhancement in Calix[4]arene-Functionalized Titanium-Oxo Clusters.

Incorporating two organic ligands with different functionalities into a titanium-oxo cluster entity simultaneously can endow the material with their respective properties and provide synergistic performance enhancement, which is of great significance for enriching the structure and properties of titanium-oxo clusters (TOCs). However, the synthesis of such TOCs is highly challenging. In this work, we successfully synthesized a TBC4A-functionalized TOC, [Ti2(TBC4A)2(MeO)2] (Ti2; MeOH = methanol, TBC4A = tert-butylcalix[4]arene). By adjusting the solvent system, we successfully introduced 1,10-phenanthroline (Phen) and prepared TBC4A and Phen co-protected [Ti2(TBC4A)2(Phen)2] (Ti2-Phen). Moreover, when Phen was replaced with bulky 4,7-diphenyl-1,10-phenanthroline (Bphen), [Ti2(TBC4A)2(Bphen)2] (Ti2-Bphen), which is isostructural with Ti2-Phen, was obtained, demonstrating the generality of the synthetic method. Remarkably, Ti2-Phen demonstrates good stability and stronger light absorption, as well as superior photoelectric performance compared to Ti2. Density functional theory (DFT) calculations reveal that there exists ligand-to-core charge transfer (LCCT) in Ti2, while an unusual ligand-to-ligand charge transfer (LLCT) is present in Ti2-Phen, accompanied by partial LCCT. Therefore, the superior light absorption and photoelectric properties of Ti2-Phen are attributed to the existence of the unusual LLCT phenomenon. This study not only deeply explores the influence of Phen on the performance of the material but also provides a reference for the preparation of materials with excellent photoelectric performance.

Enzyme mimicking activity of the Ru(pic)3 complex in the oxidation NADH coenzymes: kinetic and mechanistic studies

Mimicking the enzymatic oxidation of NADH and obtaining mechanistic insight into the electron transfer reaction pertinent to the redox inter-conversion of NADH/NAD+ couple is a long-term challenge in biological and energy-related chemistry. The kinetics and mechanism of the oxidation of NADH by [RuIII(pic)3] (pic– = picolinate anion) has been studied spectrophotometrically and kinetically in aqueous solution at pH 7.0 (MES buffer). The reaction was followed over time at 466 nm (metal to ligand charge transfer band of [RuII(pic)3]–). The rate of NADH oxidation was found to be first-order with respect to Ru(III)-complex concentration. The values of the observed rate constant (k obs) increased linearly with increase in the concentration of NADH. The rate of the reaction was independent of the ionic strength of the reacting solution. Activation parameters (ΔH≠ = 56 ± 1 kJ mol−1 and ΔS≠ = −65 ± 3 J.deg−1 mol−1) were determined from the temperature dependence studies (15-35 °C) of the reaction. Kinetic data and activation parameters are interpreted in terms of a mechanism involving outer-sphere electron transfer.

Cyclometalated Pt(II)C^N phosphors bearing a bis(diphenylphorothioyl) amide ligand: synthesis and photophysical properties

Six Pt(II) complexes bearing a primary phenylpyridine (ppy) ligand or a ppy derivative and two Pt(II) complexes bearing a primary 8-hydroxyquinoline (hqnl) or 7-bromo-8-quinolinol ligand have been prepared via coordination with an auxiliary bis(diphenylphosphothionyl) amide (HStpip) ligand. All eight complexes were characterized by NMR (1H,13C, and 31P), HRMS, and elemental analysis. In addition, complexes 2, 4, 5, and 8 were characterized by single crystal XRD. The eight complexes were not emissive in solution under N2 at room temperature (r.t.). However, they all exhibited an intense emission in the solid state and in 2 wt.% polymethyl methacrylate (PMMA) films. In particular, 5 bearing a primary 2-([1,1'-biphenyl]-3-yl)-4-phenylpyridine ligand exhibited a triplet emission at 525 and 552 nm with a quantum yield of 80% in pure solid state. Density functional theory (DFT) and time dependent (TD) DFT calculations were performed for optimization and predicting the excitation properties of 2, 4, 5, and 8. The computational results reveal that the intrinsic triplet emissions of 2, 4, and 5 are the result of combinations of ligand-to-metal charge transfer (LMCT) (π*(ppy) → d(Pt)) and ligand-to-ligand charge transfer (LLCT) (π*(ppy) → p(Stpip)), whereas the triplet emission of 8 shows a π*–π character with a small LMCT (π*(hqnl) → d(Pt)) component.