Charge-transfer Complexes Research Articles

Charge Transfer Interaction Dynamics between 2-Methyl-8-hydroxyquinoline and 2,4-Dinitrophenol: Synthesis, Spectroscopic Characterization, DNA Binding and DFT Studies

A novel charge transfer (CT) complex was formed by combining the electron-acceptor 2,4-dinitrophenol (DNP) with the electron-donor 2-methyl-8-hydroxyquinoline (MHQ). The complex obtained was further characterized using both experimental and theoretical methods. The Benesi-Hildebrand equation can be utilized to determine various spectroscopic physical measurements such as the molar absorptivity (εCT) and formation constant (KCT). The CT complex has a stoichiometry of 1:1. Multiple spectroscopic methods were employed to investigate the resultant solid compound. The existence of charge and proton transfer in the resultant complex was confirmed by FT-IR, 1H NMR, SEM-EDX and powder-XRD studies. An electron absorption spectroscopy examination was done to analyze the complex DNA binding capability. The resulting complex was determined to have an intercalative binding mechanism, with an intrinsic binding constant (Kb) value of 4.2 × 106 M-1. The experimental results were corroborated by performing theoretical calculations using DFT using a CAM-B3LYP/6-31G(d,p) basis set. The geometrical parameters, electrostatic potential maps (MEPs) and Mullikan charges were computed and examined in agreement with the experimental observations. In addition to electron transmission, the stability of the complex is influenced by the presence of a hydrogen bond.

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.

Wide-range tunable circularly polarized luminescence in triphenylamine supramolecular polymers via charge-transfer complexation

Wide-range tunable circularly polarized luminescence in triphenylamine supramolecular polymers via charge-transfer complexation

Development of novel DNA aptamers and colorimetric nanozyme aptasensor for targeting multi-drug-resistant, invasive Salmonella typhimurium strain SMC25

Invasive, biofilm-forming Non-typhoidal Salmonella (iNTS), propagating through the global food and water supply chain, presents a significant risk to food safety and public health. Developing a robust detection system is crucial for enabling point-of-care, affordable, and equipment-free identification of this pathogen throughout the supply chain. In this study, we screened a novel pool of ssDNA aptamers specific to a multidrug resistant iNTS strain SMC25, previously isolated from Indian poultry products in our earlier research. Through 13 rounds of whole-cell SELEX, we identified, characterized, and selected seven full-length aptamers (ST18, ST19, ST25, ST28, ST29, ST31, and ST32). Flow cytometric analysis reveals superior binding of ST25, ST28, ST29, and ST31. These aptamers were translated onto Nanozyme-based aptasensing system for efficient, cost-effective detection of SMC25. This system harnesses the aptamer-mediated, reversible peroxidase-like activity of gold nanoparticles (GNPs) to oxidize the TMB substrate into a one-electron oxidation state, resulting in a blue-colored Diamine charge transfer complex (DCTC). The catalytic process, coupled with GNP aggregation, induces a visible color change in the test mixture from ruby-red to blue. Post-SELEX truncations identified the optimal aptamer sequence (T_ST31), which selectively detected SMC25 in water with a limit of detection (LOD) of ∼10⁴ CFU/mL. Lower concentrations (10 CFU/mL) of SMC25 could be detected after non-selective enrichment within 120 min. This research introduces a novel pool of iNTS-specific aptamers along with a cost-effective (0.25 USD per sample) solution for colorimetric detection by the naked eye.

Photocatalysis of Adsorbed Catechol on Degussa P25 TiO2 at the Air-Solid Interface.

Semiconductor photocatalysis with commercial TiO2 (Degussa P25) has shown significant potential in water treatment of organic pollutants. However, the photoinduced reactions of adsorbed catechol, a phenolic air pollutant from biomass burning and combustion emissions, at the air-solid interface of TiO2 remain unexplored. Herein we examine the photocatalytic decay of catechol in the presence of water vapor, which acts as an electron acceptor. Experiments under variable cut-off wavelengths of irradiation (λcut-off ≥ 320, 400, and 515 nm) distinguish the mechanistic contribution of a ligand-to-metal charge-transfer (LMCT) complex of surface chemisorbed catechol on TiO2. The LMCT complex injects electrons into the conduction band of TiO2 from the highest occupied molecular orbital of catechol by visible light (≥2.11 eV) excitation. The deconvolution of diffuse reflectance UV-visible spectral bands from LMCT complexes of TiO2 with catechol, o-semiquinone radical, and quinone and the quantification of the evolving gaseous products follow a consecutive kinetic model. CO2(g) and CO(g) final oxidation products are monitored by gas chromatography and Fourier-transform infrared spectroscopy. The apparent quantum efficiency at variable λcut-off are determined for reactant loss (Φ- TiO2/catechol = 0.79 ± 0.19) and product growth ΦCO2 = 0.76 ± 0.08). Spectroscopic and electrochemical measurements reveal the energy band diagram for the LMCT of TiO2/catechol. Two photocatalytic mechanisms are analyzed based on chemical transformations and environmental relevance.

A Comprehensive Multireference Study of Excited-State Ni-Br Bond Homolysis in (dtbbpy)NiII(aryl)(Br).

The mechanism of visible light-driven Ni-C(aryl) bond homolysis in (2,2'-bipyridine)NiII(aryl)(halide) complexes, which play a crucial role in metallaphotoredox catalysis for cross-coupling reactions, has been well studied. Differently, the theoretical understanding of Ni-halide bond homolysis remains limited. In this study, we introduce a novel electronic structural framework to elucidate the mechanisms underlying photoinduced Ni-Br bond rupture in the (dtbbpy)NiII(aryl)(Br) complex. Using multireference ab initio calculations, we characterized the excited state potential energy surfaces corresponding to metal-to-ligand charge transfer (MLCT) and ligand-to-metal charge transfer (LMCT). Our calculations reveal that the Ni-Br dissociation, triggered by an external photocatalyst, begins with the promotion of Ni(II) to a 1MLCT excited state. This state undergoes intersystem crossing with repulsive triplet surfaces corresponding to the 3MLCT and Br-to-Ni 3LMCT states, resulting in Ni-Br bond breaking via the Dexter energy transfer mechanism. In the absence of a photocatalyst, the photoexcited Ni(II) favors Ni-C(aryl) homolysis, whereas the presence of a photocatalyst promotes Ni-Br dissociation. The Ni(III) species, resulting from the oxidation of Ni(II) by the photocatalyst, was found to be unproductive toward Ni-Br or Ni-C(aryl) activation.

Solvent assisted mechanochemical synthesis, antimicrobial and antioxidant studies of Ni2+, Mn2+, Cr<sup>2+</sup> , and Cu<sup>2+</sup> Metal complexes of some ligands derived from l-histidine and l-alanine

Mechanochemistry enables rapid, quantitative reactions to occur at or close to 27℃. It is a one-step process that allows for reactant homogenization, product nucleation, and particle growth. These processes use little or no solvent, making them less wasteful and more environmentally friendly than solvent-based reactions. Ni2+ , Mn2+, Cr2+and Cu2+ metal ions were synthesized by grinding in an agate mortar with pestle using ligands derived from amino acids (Histidine &Alanine) which were further synthesized to form complexes. The entire experiment was carried out by solvent solvent-assisted mechanochemical process and ethanol was used as liquid liquid-assisted solvent. The complexes were characterized by IR spectroscopy, U-V spectroscopy, X-ray analysis, melting point, solubility test, and conductivity measurement. The Solubility test showed that the complexes are soluble in DMSO, DMF, and ethanol and are insoluble in both hexane and tetrachloromethane. The molar conductivity values are in the range of (6.05-28.56) Ω-1cm2mol-1 ) indicating the complexes behave as non-electrolytes. IR analysis showed a vibrational frequency band observed at (1620-1625) cm-1 which is assigned to the ʋ(C=N) of the azomethine, also the new bands M=N, M=O indicate the coordination reaction between the metal and the ligands. The UV visible analysis shows various transitions, the metal complexes showed adsorption bands at λ of 420 and 575nm respectively because of the ligand-to-metal charge transfer (LMCT). The XRD analysis showed that there was a change in phase between the starting material and the product which indicate that a reaction occurred, also the nature of the spectra showed that the compounds are all crystalline. The Antimicrobial activity showed that both the complexes and the ligands have good activity against the bacterial isolates. Antioxidant activity was also tested and the compound appeared to have moderate scavenging activities compared to the reference used. The values indicated that the activities are more pronounced when coordinated with metal ions.

Ancillary Ligand-Promoted Charge Transfer in Bis-indole Pyridine Ligand-Based Nickel Complexes.

There is growing demand for the utilization of first-row transition metal complexes in light-driven processes instead of their conventional noble metal counterparts due to the greater sustainability of first-row transition metal complexes. However, their major drawback is the ultrafast lifetime of the electronic excited states of these first-row transition metal complexes, particularly those of d8 square-planar systems such as Ni(II) complexes, wherein low-lying metal-centered (MC) states provide the deactivation pathway. To increase the excited-state lifetime and broaden their applications, it is important to develop sterically bulky, strong field ligands with low-lying π* orbitals and a highly σ-donating nature to augment the energy of MC states. The current strategy relies on synthetically carbene-based ligands, which are substitutionally cumbersome and act as σ-donors only. In this work, we introduce a bis-indole pyridine (H2BIP) ligand framework, whose dianionic congener (BIP) demonstrates the ability to form stronger covalent bonds with a Ni(II) center compared to neutral donors like carbene and its effect on the complex to produce a less distorted excited-state structure. When conjoined with ancillary ligands such as pyridine or lutidine, the BIP ligand orchestrates the formation of low-energy 3CT states, which decay in ∼40 ps.

Sunlight-Driven Direct/Mediated Electron Transfer for Cr(VI) Reductive Sequestration on Dissolved Black Carbon-Ferrihydrite Coprecipitates.

Surface runoff horizontally distributed chromium (Cr) pollution into various surface environments. Sunlight is a vital factor for the Cr cycle in the surface environment, which may be affected by photoactive substances such as ferrihydrite (Fh) and dissolved black carbon (DBC). Herein, sunlight-driven transformation dynamics of Cr species on DBC-Fh coprecipitates were studied. Under sunlight, the removal of aqueous Cr(VI) by DBC-Fh coprecipitates occurred through sunlight-driven reductive sequestration including adsorption, followed by surface reduction (pathway 1) and aqueous reduction, followed by precipitation (pathway 2). Additionally, coprecipitates with a higher DBC content exhibited a more effective reduction of both adsorbed (kapp,S_red) and aqueous Cr(VI) (kapp,A_red). Photoelectrons facilitated Cr(VI) reduction through direct electron transfer; notably, electron donating DBC promoted the production of photoelectrons by consuming photogenerated holes. Photogenerated Fe(II) species (mineral-phase and aqueous Fe(II)) mediated electron transfer for Cr(VI) reduction, which was reinforced via a ligand-to-metal charge transfer (LMCT) process between DBC-organic ligands and mineral Fe(III). Furthermore, ·O2- also mediated Cr(VI) reduction, although this impact was limited. Overall, this study demonstrates that photoelectrons and photogenerated electron mediators play a crucial role in Cr(VI) reductive sequestration on DBC-Fh coprecipitates, providing new insights into the geochemical cycle of Cr pollution in sunlight-influenced surface environments.

Low-Dispersity Polymers via Free Radical Alternating Copolymerization: Effects of Charge-Transfer-Complexes.

Alternating copolymers are crucial for diverse applications. While dispersity (Ð, also known as molecular weight distribution, MWD) influences the properties of polymers, achieving low dispersities in alternating copolymers poses a notable challenge via free radical polymerizations (FRPs). In this work, we demonstrated an unexpected discovery that dispersities are affected by the participation of charge transfer complexes (CTCs) formed between monomer pairs during free radical alternating copolymerization, which have inspired the successful synthesis of various alternating copolymers with low dispersities (>30 examples, Ð=1.13-1.39) under visible-light irradiation. The synthetic method is compatible with binary, ternary and quaternary alternating copolymerizations and is expandable for both fluorinated and non-fluorinated monomer pairs. DFT calculations combined with model experiments indicated that CTC-absent reaction exhibits higher propagation rates and affords fewer radical terminations, which could contribute to low dispersities. Based on the integration of Monte Carlo simulation and Bayesian optimization, we established the relationship map between FRP parameter space and dispersity, further suggested the correlation between low dispersities and higher propagation rates. Our research sheds light on dispersity control via FRPs and creates a novel platform to investigate polymer dispersity through machine learning.

Investigating the effect of Cu underlayer and FTO etching towards photoelectrochemical performance enhancement of Cu2O photoelectrode

Cuprous oxide (Cu2O) exhibits potential as a photoactive material for photoelectrochemical water splitting, owing to its appropriate bandgap, efficient charge carrier separation, and ability to enhance solar-driven hydrogen production. This study investigates the influence of substrate etching, Cu underlayer and Cu2O electrodeposition time, and annealing time on enhancing the photoelectrochemical (PEC) performance. Electrodeposition and thermal oxidation techniques were used to fabricate the Cu2O/Cu/FTOe-A photocathode. It has been observed that FTO etching improves adhesion, light transmission, and efficiency. A Cu underlayer also impacts the PEC performance, wherein an ideal thickness of Cu leads to enhanced PEC performance. This study also focuses on the annealing time that leads to CuO layers and nanowires forming on the Cu2O surface. The structural and chemical changes before and after annealing are confirmed via XRD, XPS, AFM and FESEM analyses. UV–Vis analysis also reveals that the presence of Cu underlayer, FTO etching, and the annealing process affect the electrical properties and light absorption capacities of the Cu2O photoelectrode. Electrochemical impedance analysis (EIS) and Mott-Schottky analysis have provided insights into the enhanced charge transfer properties and band bending in the Cu2O/Cu/FTOe-A, resulting in enhanced PEC performance. Overall, this study provides significant insights into the understanding and enhancement of Cu2O/Cu/FTOe-A photocathodes for potential use in PEC water splitting applications.

Energy transfer-mediated multiphoton synergistic excitation for selective C(sp3)–H functionalization with coordination polymer

Activation and selective oxidation of inert C(sp3)–H bonds remain one of the most challenging tasks in current synthetic chemistry due to the inherent inertness of C(sp3)–H bonds. In this study, inspired by natural monooxygenases, we developed a coordination polymer with naphthalenediimide (NDI)-based ligands and binuclear iron nodes. The mixed-valence FeIIIFeII species and chlorine radicals (Cl•) are generated via ligand-to-metal charge transfer (LMCT) between FeIII and chlorine ions. These Cl• radicals abstract a hydrogen atom from the inert C(sp3)–H bond of alkanes via hydrogen atom transfer (HAT). In addition, NDI converts oxygen to 1O2 via energy transfer (EnT), which then coordinates to FeII, forming an FeIV = O intermediate for the selective oxidation of C(sp3)–H bonds. This synthetic platform, which combines photoinduced EnT, LMCT and HAT, provides a EnT-mediated parallel multiphoton excitation strategy with kinetic synergy effect for selective C(sp3)–H oxidation under mild conditions and a blueprint for designing coordination polymer-based photocatalysts for C(sp3)–H bond oxidation.

N-Halosuccinimide-CeCl3 Transient Charge-Transfer Complexes as Semi Heterogeneous Photocatalyst in Cyclization of N-Propargylamides.

In this work, we used photoinert anhydrous cerium(III) chloride, to form a transient charge-transfer (CT) complex with NXS (N-bromosuccinimide or NBS and N-iodosuccinimide or NIS) in acetonitrile. These transient CT complexes acted as a semi-heterogeneous photocatalyst. These complexes allowed the Ce(III) ions to absorb light, turning them into strong electron donors that transferred electrons to NXS. This created halide radicals from NXS radical anions, helping to turn N-propargylamides into oxazole aldehydes. Experiments with DMPO and spin-trapping showed that a radical-based mechanism followed a single electron transfer (SET) pathway. Notably, CeCl3 was reused after the reaction without much decomposition, as it was regenerated and separated through simple filtration.

Tetraphenylethene-Based Ni8-Pyrazolate Metal-Organic Framework for Photoredox/Nickel Dual Catalysis of C-S Cross-Coupling.

As a prototypical aggregation-induced emission luminogen (AIEgen), the tetraphenylethene (TPE) moiety has been judiciously modified as organic linkers for constructing various functional metal-organic frameworks (MOFs). However, these AIEgen-based MOFs have rarely received research attention in photocatalytic applications due to their limited stability in harsh reaction conditions. In this work, we report a robust Ni8-pyrazolate-based MOF (denoted as TPE4Pz-Ni) under the guidance of reticular chemistry, which is assembled by an AIE-active tetratopic linker of 1,1,2,2-tetrakis(4-(1H-pyrazol-4-yl)phenyl)ethane (H4-TPE4Pz) with a 12-connected Ni8-cluster of [Ni8(OH)4(H2O)2Pz12] (Pz = pyrazolate) in a (4,12)-connected ftw-a topological network. Notably, MOF TPE4Pz-Ni exhibits excellent stability in a wide range of solvents and even in a saturated NaOH solution. Moreover, its luminescent emission is effectively quenched via a ligand-to-metal charge transfer (LMCT) process originating from the TPE-cored linker to the Ni8 cluster, which enables TPE4Pz-Ni to act as an efficient photoredox/nickel dual catalyst for light-mediated C-S cross-coupling reactions between various aryl iodides and thiols.

Optimizing ligand-to-metal charge transfer in metal–organic frameworks to enhance photocatalytic performance

Metal-organic frameworks (MOFs) have been widely investigated as active photocatalytic material for energy conversion and environmental purification. This review meticulously examines the charge transfer mechanisms within MOFs upon photoexcitation, with a particular emphasis on ligand-to-metal charge transfer (LMCT) and metal-to-ligand charge transfer (MLCT). These processes are essential for the generation and maintenance of effective charge separation, wherein LMCT is especially critical for the photocatalytic applications of MOFs. The analysis begins with an exploration of the charge transfer mechanisms within the MOFs’ structure, assessing the impact of various factors on LMCT, including the metal center, ligand structure, overall spatial configuration and reaction environment. Furthermore, the review provides an in-depth exploration of the advantages and applications of LMCT in photocatalysis. It concludes with an outlook on the future development of LMCT in the field of photocatalysis, underscoring its transformative potential with ongoing research and innovation.

Synthesis and Optical Properties of Organic-Inorganic Hybrid[(18-Crown-6)K][MoOCl4(H2O)

Crown ether anchored organic-inorganic hybrid halides have been recently reported as interesting luminescent materials in the visible region of electromagnetic spectrum. Is it possible to develop such crown ether anchored hybrid materials for near infrared emission? Motivated by this question, we designed a new hybrid material, namely, [(18-Crown-6)K][MoOCl4(H2O)]. 18-Crown-6 ether bound with K+ form the cationic part [(18-Crown-6)K]+. The K+ of [(18-Crown-6)K]+ electrostatically interacts with Cl- of the anionic part [MoOCl4(H2O)]-, forming the hybrid crystal [(18-Crown-6)K][MoOCl4(H2O)]. It crystallizes in orthorhombic crystal system with Pnma space group. The Mo(V) possesses one d-electron (d1) in C4v point group symmetry in the [MoOCl4(H2O)]- polyhedra. This electronic configuration leads to multiple spin-allowed d-d transitions along with a ligand to metal charge transfer (LMCT) resulting into multiple optical absorption bands in the near UV-visible-near infrared (NIR) region. The lowest energyd-dtransition via 2E to2B2 leads to NIR PL with peak at 952 nm, but with a poor intensity at room temperature.

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.

Metal-Ligand Covalency in the Valence Excited States of Metal Dithiolenes Revealed by S 1s3p Resonant Inelastic X-ray Scattering.

Metallo dithiolene complexes with biological and catalytic relevance are well-known for having strong metal-ligand covalency, which dictates their valence electronic structures. We present the resonant sulfur Kβ (1s3p) X-ray emission spectroscopy (XES) for a series of Ni and Cu bis(dithiolene) complexes to reveal the ligand sulfur contributions to both the occupied and unoccupied valence orbitals. While S K-edge X-ray absorption spectroscopy played a critical role in identifying the covalency of the unoccupied orbitals of metal dithiolenes, the present focus on XES explores the occupied density of states. For a series of [Cu(mnt)2]n- and [Ni(mnt)2]n- anions and dianions, a comparison of the nonresonant and resonant S Kβ XES spectra highlights the dramatic improvement in spectral resolution and corresponding ability to differentiate subtle changes in occupied electronic structure across the series. Furthermore, the use of resonant inelastic X-ray scattering (RIXS) probes the valence excited states and the core-valence couplings of the complexes. By employing a theoretical approach based on time-dependent density functional theory to interpret the RIXS spectra, we reveal how metal-ligand covalency influences the excited state energies and covalencies. We identify the low energy excited states as having the same symmetry as the nominal "ligand field" or "d-d" states that typically dominate the photophysics of 3d metal complexes but with significant metal-ligand charge transfer character dictated by their covalency. These results suggest that strong metal-ligand covalency can be used to influence the charge-transfer photochemistry of first row transition metal complexes.

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).

Dy3+-doped niobate phosphor based on charge transfer band red-shift effect: Luminescence thermal stability and temperature sensing performance

The thermal quenching behavior seriously limits the application prospect of phosphors, so it is urgent to improve the thermal quenching behavior of phosphors. It is expected that the red-shift of charge transfer band (CTB) caused by temperature can be used to improve the luminescent stability of phosphor. Therefore, we designed a family of LuNbO4:x%Dy3 (x = 0.25, 1, 2, 5) phosphors based on the characteristic of the red-shift of CTB edge, and investigated the relationship between the red-shift of the CTB edge and the luminescence thermal stability of the phosphor, further broadening the application of this phosphor in temperature sensing. The effects of three different excitation positions, CTB (260 nm), CTB edge red-shift (288 nm) and Dy3+ 4f-4f transition (354 nm), on the luminescence thermal stability of phosphors were also investigated. It was found that only excitation in the red-shift range of CTB edge showed complete antithermal quenching behavior. The LuNbO4:2 %Dy3+ phosphor showed complete antithermal quenching under the excitation of CTB edge, and the comprehensive emission intensity at 573 K is 741 % of that at 298 K. According to the above characteristics, a dual-mode optical thermometry based on fluorescence intensity ratio (FIR) and International Commission on Illumination (CIE) chromaticity coordinates is proposed, in which the maximum relative temperature sensitivity of LuNbO4:x%Dy3+ is 5.04 % K−1 (298 K, FIR) and 3.14 % K−1 (573 K, CIE). Interestingly, when constructing CIE temperature measurement model, we found that LuNbO4:0.25 %Dy3+ phosphor at 260 nm excitation position has obvious color change at each temperature stage, showing temperature visualization characteristics. At 354 nm excitation position, it shows constant white light emission. The excellent optical temperature measurement performance and temperature visualization characteristics of the phosphor shows that it has excellent application potential in optical sensing.