Charge Transfer Transitions Research Articles

Heteroleptic Cu(I) complex with vapochromism and its application as electrochromic material

Heteroleptic Cu(I) complex with vapochromism and its application as electrochromic material

Investigating spectroscopic properties, biological effects, and molecular docking studies of synthesized Schiff base metal complexes

In this current investigation, we have accomplished the synthesis of a Schiff base ligand termed (E)-4-methyl-N′-(2,4,5-trimethoxybenzylidene)benzohydrazide (HL) through a reversible condensation reaction, which engaged a carbonyl compound and a primary amine. This synthesized Schiff base ligand, HL, served as the foundation for the preparation of two metal complexes, namely, M1L (Cu complex) and M2L (La complex). To characterize these compounds, we employed various analytical techniques, including thermogravimetric studies, elemental analysis, powder X-ray diffraction, FT-IR spectroscopy and 1H NMR. The examination of powder X-ray diffraction data provided valuable insights into the crystalline structures of the Cu and La complexes. These shifts are indicative of structural changes in the complexes. Our electronic spectrum analysis revealed the pivotal involvement of the ligand in promoting charge transfer processes, substantiated by an increased concentration of charge transfer transitions observed when the ligand was present. Additionally, we evaluated the antibacterial efficacy of the Schiff base ligand HL and its metal complexes (Cu, La) against a spectrum of bacteria, encompassing both gram-positive (Bacillus subtilis, Enterococcus faecalis) and gram-negative (Escherichia coli) strains. In the current investigation, we utilized molecular docking techniques to explore the interactions between the synthesized HL and its M1L and M2L complexes with protein receptor molecules. These results highlighted the favorable binding energies and stable interactions of these compounds with the protein receptor, M1L displayed notably more stable interactions and lower binding energy compared to M2L. This suggests that M1L may have a stronger potential impact on the free binding energy and molecular interactions.

Structurally diverse macrocycle co-crystals for solid-state luminescence modulation

Organic co-crystals offer an opportunity to fabricate organic functional materials. Traditional co-crystals are generally packed following the segregated or mixed stacking mode, leading to the lack of structural and functional diversity. Herein, we report three sets of macrocycle co-crystals with identical co-constitutions. The macrocycle co-crystals differ in the stoichiometric ratios (2:1, 1:1, and 2:3) of the constituents and molecular packing modes. The co-crystals are constructed using triangular pyrene-macrocycle and 1,2,4,5-tetracyanobenzene exploiting exo-wall charge-transfer interactions. Interestingly, the three co-crystals exhibit distinct, tunable emission properties. The corresponding emission peaks appear at 575, 602, and 635 nm, covering yellow via orange to red. The X-ray diffraction analyses and the density functional theory calculations reveal the superstructure-property relationships that is attributed to the formation of different ratios of charge-transfer transition states between the donor and acceptor motifs, resulting in red-shifted luminescence.

Optical and ferroelectric properties of lead titanate nanocrystals dispersed within borate glass matrix

Lead titanate nanocrystals dispersed within the borate glass matrix (composite) with the composition 75 B2O3-25 PbTiO3 (in mol %) was prepared. The composite's XRD analysis indicated it contains glassy phase, and this was further confirmed by DSC study. TEM, SAED, and FTIR analyses provided evidence that the PbTiO3 nanocrystals dispersed within the borate glass matrix, establishing the composite nature of this sample. The average particle size found of PbTiO3 was determined to be 57.2 nm via TEM. The composite's FTIR analysis indicated the presence of BO3 with NBO's, and BO4 units. Additionally, the presence of the Ti3+ ions in TiO6 units as well as Ti4+ ions in TiO4 and TiO6 units. The Curie temperature (Tc) of PbTiO3 in present composite sample was confirmed through both DSC and dielectric studies. Optical analysis of this composite sample unveiled three transmission bands, one corresponding to the 3Γ5 →2Γ3 charge transfer transition between Ti3+ and Ti4+ions. While the other transitions 2B2g →2B1g and 2B2g →2A1g are corresponding to the octahedral of Ti3+ (3d1) ions in tetragonal distorted sites. The polarization-field (P-E) loops of this composite sample at various electric fields unveiled relatively narrow hysteresis loops.

Copper(I) photosensitizer-silica nanoparticle assembly towards enhanced aqueous photoluminescence

Harnessing the luminescence potential of Cu(I) complexes in aqueous media is typically hindered by their poor photostability and altered properties. Here, we report the synthesis, engineering and morphological characterization of a hydrophobic homoleptic copper(I) complex entrapped into silica nanoparticles, Cu-I@SiO2 (where “Cu-I” designates [Cu(2,9-diiodo-1,10-phenanthroline)2]+), as a promising stabilisation strategy towards water-compatible, Cu(I) complex-based luminescence. The polyether chain-decorated nano-objects are spherical with an average diameter of ca. 10.8 ± 1.9 nm. Upon dispersion in water, clear solution-like suspensions were obtained. Significantly, the aqueous suspensions photo-luminesce (Φem = 5×10-4) upon excitation through the Metal-to-Ligand Charge-Transfer transition (MLCT) of the embedded copper(I) complexes. In contrast, the corresponding silica-free molecular complex dissolved in an aqueous environment revealed fully quenched emission. Finally, the use of Cu-I@SiO2 suspensions as luminescent probes is reported, first by assessing their potential use as electrochemiluminescent probes, and second by monitoring the photoluminescence from Cu-I@SiO2 in the presence of whole blood.

Hollow gold nanoparticles coated with ZnS with distance-dependent plasma coupling and surface enhanced Raman spectroscopy for applications

Metal@semiconductor core-shell heterostructure with strong exciton-plasmon coupling can integrate multiple functions of each component and exhibit extraordinary benefits in the optical, catalytic, electrical, and magnetic properties due to its excellent synergistic properties at the heterointerfaces. In our work, hollow gold nanoparticles (HGNs)- 4-mercaptobenzoic acid (MBA) @ZnS core-shell heterostructure with the adjustable shell thickness (tshell) of ZnS varied from 1 to 19 nm were successfully prepared for the first time by low temperature and simple two-step method. Here, we report our findings that the surface enhanced Raman scattering (SERS) spectral intensity of HGNs-MBA@ZnS under the 633 nm excitation correlates with the tshell of ZnS, and the experimental results are consistent with theoretical studies. Furthermore, we also investigated the excitation wavelength-dependent SERS enhancement mechanism of HGNs-MBA@ZnS (tshell = 2 nm) and the result showed that the near-field enhancement and plasmon-induced interfacial charge transfer transition (PICTT) synergistically increase the SERS intensity under the excitation line at 633 nm. Our work not only provides guidance for the design and synthesis of other important metal@semiconductor core-shell heterostructure, but presents significant insights into their SERS enhancement mechanism.

Coumarin Linked Cyanine Dye for the Selective Detection of Cyanide Ion in Environmental Water Sample.

A benzoxazole-coumarin-based probe BOC, was synthesized and validated for its anion sensing ability and found to be effective in recognizing cyanide ions. Upon addition of cyanide, a spontaneous color change was observed that was visible to the naked eye. The sensitization process takes place with nucleophilic addition, and the cyanide ion added to the probe disrupts the intra molecular charge transfer transition (ICT) between the donor and acceptor units, causing the pink colored probe to become yellow. Ultraviolet and fluorescence methods were applied to measure the detection limits of probes with added cyanide ions, which were found to be 3.47 µM and 2.48 nM. The stoichiometry of the probe with the cyanide ion was determined by the Job's method, NMR titration, and mass spectrometry and was found to be in a 1:1 ratio. The results obtained from the visual and UV-visible spectral studies are justified by theoretical calculations. The cyanide-loaded probe induced visual changes, which enabled the development of a test strip for field application, and the prepared strip can be used to detect the ppm level of cyanide in water samples. The developed probe, BOC, can be used to detect cyanide ions in various water samples.

Fluorine doping induced fluorescence emission redshift of CDs

Elemental doping is an effective way to modify the optical properties of carbon dots (CDs). In this work, the effects of fluorine-doped (F-doped) types and configurations on the structural stability and fluorescence properties of CDs were investigated based on density functional theory and time-dependent density functional theory. Circumcoronene was selected as an undoped structure, and a series of F-doped CD structures including edge and basal plane fluorine-doping (F-doping) types, and CF, CF2 and CF3 configurations were constructed. The calculation results show that the edge CF groups play a more positive role in the structural stability of CDs than the CF2 and basal plane CF groups. Different from the three configurations, the CF3 groups cannot contribute to the structural stability. For optical properties, the edge CF and CF3 groups have less effect on the electron distribution of CDs, hence only a slight fluorescence emission redshift occurs in two F-doping cases. In contrast, the CF2 and basal plane CF groups can evidently influence the highest occupied molecular orbital of the CDs, which induces the charge transfer transition and the fluorescence emission is redshifted to the near-infrared region. This work is helpful to predict the F-doped types and configurations in CDs, reveals the modulation mechanism of F-doping on the fluorescence properties and provides a theoretical guidance for the controlled synthesis of CDs in the future.

Investigation of Pressure Effects in the Bimetallic Transplutonium Tetrazolate Complexes [(An(pmtz)2(H2O)3)2(μ-pmtz)]2(pmtz)2·nH2O (An3+ = Cm3+, Bk3+, and Cf3+).

Understanding the effects of pressure on actinide compounds is an integral part of safe nuclear waste storage in deep geologic repositories and provides a means of systematically altering the structure and properties. However, detailing how the effects of pressure evolve across the actinide series in the later elements is not typically undertaken because of the challenges of conducting research on these unstable isotopes. Here, a family of bimetallic actinide complexes, [(An(pmtz)2(H2O)3)2(μ-pmtz)]2(pmtz)2·nH2O (An3+ = Cm3+, Bk3+, and Cf3+, pmtz- = 5-(pyrimidyl)tetrazolate; Cm1, Bk1, and Cf1), are reported and represent the first structurally characterized bimetallic berkelium and californium compounds. The pressure response as determined from UV-vis-NIR transitions varies for Cm1, Bk1, and Cf1. The 5f → 5f transitions in Cm1 are notably more sensitive to pressure compared to those in Bk1 and Cf1 and show substantial bathochromic shifting of several 5f → 5f transitions. In the case of Bk1, an ingrowth of a metal-to-ligand charge-transfer transition occurs at elevated pressures because of the accessible Bk3+/Bk4+ couple. For Cf1, no substantial transition shifting or emergence of MLCT transitions is observed at elevated pressures because of the prohibitive energetics of the Cf3+/Cf4+ couple and reduced sensitivity of the 5f → 5f transitions to the local coordination environment because of the more contracted 5f shell versus Cm3+ and Bk3+.

Fe(III) Bis-Alkynyls Supported by the TIM Macrocycle: Molecular and Electronic Structures and Altering the Nature of Charge Transfer Transitions through Reduction

Fe(III) Bis-Alkynyls Supported by the TIM Macrocycle: Molecular and Electronic Structures and Altering the Nature of Charge Transfer Transitions through Reduction

Synthesis, Optical, Dielectric, SHG, Magnetic and Visible Light Driven Catalytic Studies on Compounds Belonging to the Swedenborgite Structure.

A new compound, InBaZn3GaO7, with swedenborgite structure along with transition metal (TM) substituted variants have also been prepared. The structure contains layers of tetrahedral ions (Zn2+/Ga3+) connected by octahedrally coordinated In3+ ion forming the three-dimensional structure with voids where the Ba2+ ions occupy. The TM substituted compounds form with new colors. The origin of the color was understood based on the ligand-field transitions. The near IR reflectivity studies indicate that the Ni - substituted compounds exhibit good near - IR reflectivity behavior, making them possible candidates for 'cool pigments'. The temperature dependent dielectric studies indicate that the InBaZn3GaO7 compound undergoes a phase transition at ~360 °C. The compounds are active towards second harmonic generation (SHG). Magnetic studies show the compounds, InBaZn2CoFeO7 and InBaZn2CuFeO7 to be anti-ferromagnetic in nature. The copper containing compounds were found to be good catalysts, under visible light, for the oxidation of aromatic alkenes. The many properties observed in the swedenborgite structure-based compounds suggests that the mineral structure offers a fertile ground to investigate newer compounds and properties.

Bridge-induced taming of the visible electronic circular dichroism signatures of helicoBODIPYs

Helically-flexible bis(BODIPY)s based on chiral ethane-1,2-diamine or −1,2-diol bridges (named helicoBODIPYs) are an interesting family of accessible and tunable small multichromophoric organic dyes enabling visible electronic circular dichroism (ECD) and, even visible circularly polarized luminescence (CPL). However, their CPL brightness (BCPL) is still limited (up to ca. 10 M−1cm−1), due to low fluorescence efficiency owing to a non-optimal participation of intramolecular charge transfer (CT) emission. Herein, we analyze in depth the origin and factors controlling this CT, demonstrating the key participation of a BODIPY-to-BODIPY symmetry-breaking induced CT (SBCT), beyond the expected CT within each single BODIPY chromophore due to their push-pull character. It is also demonstrated that increasing the overcrowding at the flexible helicoBODIPY ethane bridges leads to BODIPY-BODIPY faced dispositions, promoting the SBCT and enabling the detection of both CT absorption and CT emission bands under specific conditions. Interestingly, this SBCT enhances the visible ECD (absolute gabs values), supporting the key role of the involved forbidden CT transitions in the chiroptical activity of these dyes, as well as the possibility of modulating their valuable visible chiroptical signatures (e.g., visible CPL brightness) by easily playing with steric factors at the dye bridge.

Optical, conductive, and ferroelectric properties of the first layer of dip-coated BiFeO3 films from methoxyethanol and acetic acid-based chemical dissolvents

The overall performance of the multilayer resulting in a sol-gel bismuth ferrite (BiFeO3) film will be primarily determined by the properties of the first layer, but this has yet to receive much attention, even though chemical and morphological defects of this layer can accumulate as the number of layers increases. Here, we perform an optical, conductive, and ferroelectric study of first layer (L 1) dip-coating sol-gel BiFeO3 films using two routes that vary only in the dissolvent; the first one is based on 2-methoxyethanol (MOE), and the second one on acetic acid (AA) with some MOE (AA-MOE). Tauc plots reveal a band gap of 2.43 eV and 2.75 eV for MOE (30 ± 5 nm thick) and AA-MOE (35 ± 5 nm thick) films, respectively. MOE films showed a dielectric function with features at ∼2.5 eV, ∼3.1 eV, and ∼3.9 eV, which were associated with charge-transfer transitions, but such features are absent in AA-MOE films. Advanced atomic force microscopy techniques were used to identify the fine features or defects of the BiFeO3 films: The conductive maps show that the charge transport pathways in both film routes are controlled by nanometer defects rather than grain or grain boundary defects. Current-voltage curves reveal high conductive pathway at a lower voltage for the MOE films than for AA-MOE films. The piezoelectric coefficient for MOE films was ∼20% higher than AA-MOE films. Both deposition methods yield ferroelectric films with an electromechanical strain controlled by the piezoelectric effect and minimal contribution from electrostriction. An optimization for the AA-MOE-based route in the withdrawal speed results in a significant reduction of morphological defects and a more than twofold increase in the piezoelectric coefficient. Our results broaden the understanding of optical and ferroelectric BiFeO3 films based on a chemical solution by dip-coating.

Intervalence Charge Transfer in Nonbonding, Mixed-Valence, Homobimetallic Ytterbium Complexes.

There are several reports of compounds containing lanthanide ions in two different formal oxidation states; however, there are strikingly few examples of intervalence charge transfer (IVCT) transitions observed for these complexes, with those few occurrences limited to extended solids rather than molecular species. Herein, we report the synthesis, characterization, and computational analysis for a series of ytterbium complexes including a mixed-valence Yb25+ complex featuring a remarkably short Yb···Yb distance of 2.9507(8) Å. In contrast to recent reports of short Ln···Ln distances attributed to bonding through 5d orbitals, the formally Yb25+ complex presented here displays clear localization of Ln2+ and Ln3+ character and yet still displays an IVCT in the visible spectrum. These results demonstrate the ability to tune the electronic structure of formally mixed oxidation state lanthanide complexes: the high exchange stabilization of the Yb2+ 4f14 configuration disfavors the formation of a 5d1 bonding configuration, and the short metal-metal distance enforced by the ligand framework allows for the first observed lanthanide IVCT in a molecular system.

Key Role of Metal-to-Metal Charge Transfer Transition between Mo6+ and Bi3+ for Enhancement in NIR Luminescence of Gd2MoO6:Bi,Yb Nanophosphor

Key Role of Metal-to-Metal Charge Transfer Transition between Mo⁶⁺ and Bi³⁺ for Enhancement in NIR Luminescence of Gd₂MoO₆:Bi,Yb Nanophosphor

Chirality Induction and Memory of Pillar[4]arene[1]quinone Derivatives in Visible-Light Range.

Pillar[4]arene[1]quinone derivatives (PQXs) were synthesized by the oxidation of pillar[5]arenes, which exhibited notable charge transfer (CT) transitions at approximately 485 nm. Successful chiral resolution of two pairs of enantiomeric conformers was achieved. Despite reduced binding affinity, PQXs demonstrated slower racemization kinetics. Visible-light chiroptical induction with a significant dissymmetry factor was attained by complexing PQXs with a chiral guest. The induced enantiomeric excess could be maintained through competitive binding with an achiral guest, offering a promising strategy for chiral sensing and memory.

Phosphorescent fac-Bis(triarylisocyanide) W(0) and Mo(0) Complexes.

Homoleptic W(0) and Mo(0) complexes containing bis(triarylisocyanide) ligands with bulky substituents were synthesized and spectroscopically characterized. Crystallographically determined structures revealed that these complexes are hourglass-like in shape with the tridentate ligands adopting a facial coordination mode to the metal center. These complexes luminesce in fluid solutions and in the solid state. Typically in toluene at 298 K, the two W(0) complexes display the emission maximum (lifetime and quantum yield) at 591 nm (0.83 μs and 0.35) and 628 nm (1.04 μs and 0.39), and similarly, the two Mo(0) complexes display it at 575 nm (0.54 μs and 0.15) and 617 nm (0.56 μs and 0.23). DFT and TDDFT calculations indicated that the low-energy absorption bands of the W(0) and Mo(0) complexes could be metal-to-ligand charge transfer (MLCT) transitions in nature. These complexes exhibited a reversible M+/0 redox couple at -0.70 and -0.63 V vs Fc+/0 for the W(0) complexes and -0.86 and -0.67 V for the Mo(0) complexes. The excited-state reduction potentials were hence estimated to be -2.91 and -2.74 V vs Fc+/0 for the W(0) complexes and -3.10 and -2.81 V vs Fc+/0 for the Mo(0) complexes, indicating that they are potentially strong photoreductants.

Temperature-responsive insights: Investigating Eu3+ and Dy3+ activated yttrium calcium oxyborate phosphors for structure and luminescence

An investigation into the luminescent behavior of YCOB (Yttrium Calcium Oxyborate) doped with Eu3+ and Dy3+ ions, synthesized via the combustion method, is presented. The study, employing X-ray diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and Energy-Dispersive X-ray Spectroscopy (EDS) analyses, confirms the structural integrity and purity of the synthesized nanophosphors. An XRD pattern exhibiting distinct crystalline peaks indicates that the dopant ions were successfully integrated into the YCOB lattice. The photoluminescence (PL) response of YCOB with Eu3+ and Dy3+ ions is thoroughly examined, uncovering distinct excitation and emission spectra. In the case of Eu3+ doping, excitation spectra reveal a significant charge transfer (CT) band at 254 nm, indicative of electron transfer between oxygen and europium ions. This CT transition enhances our understanding of the excitation behavior, with the dominant and Laporte-forbidden 5D0 → 7F2 transition. Characteristic peaks at 345 nm in the excitation spectra efficiently stimulate YCOB:Dy3+ when Dy3+ is used as a dopant. The primary emission peak at 585 nm corresponds to the hypersensitive electric dipole transition 4F9/2–6H13/2. Concentration quenching phenomena are observed, with a maximum Eu3+ concentration of 7 wt % attributed to the dipole-quadrupole interaction. Dy3+ doping, with a maximum concentration of 2 wt % primarily shows multipolar interactions, especially dipole-dipole interactions. The study extends to CIE chromaticity analysis, emphasizing Eu3+ doping's suitability for white light-emitting diode (WLED) applications and ensuring color stability. Conversely, varying Dy3+ concentrations do not yield consistent chromaticity coordinates. These findings have significant implications for the development of advanced phosphor materials across diverse applications, offering a roadmap for optimizing their optical performance.

Salicylidene‐based homoleptic metal(II) complexes: Theoretical, in silico molecular modeling and in vitro cytotoxicity studies

A series of 12 salicylidene‐based homoleptic nickel(II), copper(II) and zinc(II) complexes with the general formula [M(L1–4)2] (1–12) containing the tridentate ligands 2‐(((2‐(([1,1′‐biphenyl]‐3‐ylmethylene)amino)phenyl)imino)methyl)phenol (HL1), 2‐(((2‐(([1,1′‐biphenyl]‐3‐ylmethylene)amino)phenyl)imino)methyl)‐4‐methoxyphenol (HL2), 2‐(((2‐(([1,1′‐biphenyl]‐3‐ylmethylene)amino)phenyl)imino)methyl)‐4‐ethoxyphenol (HL3) and 2‐(((2‐(([1,1′‐biphenyl]‐3‐ylmethylene)amino)phenyl)imino)methyl)‐4‐nitrophenol (HL4) have been synthesized and characterized by spectroscopic analysis. The tridentate nature of the ligands form an octahedral geometry around the central metal ion through the phenolic oxygen via deprotonation and two azomethine nitrogen atoms. Further, the charge transfer transitions taking place in the complexes have been explained using HOMO‐LUMO analysis. The in vitro cytotoxicity activity screened by WST assay against human metastatic (MDA‐MB‐231), hepatoma (HepG2) and colorectal adenocarcinoma (CaCo2) cancerous, and normal mouse fibroblast (NIH3T3) cell lines showed higher activity for the complexes 2, 6 and 10 with respect to the standard drug 5‐fluorouracil. The AO/EB, PI, Rh123 and DCFH‐DA staining results indicated that the complexes induced anticancer activity through apoptosis. Furthermore, the complexes interact with FGFR and P13Kγ kinase receptors through the hydrophobic, hydrogen bonding, π–π, σ–π, van der Waals and electrostatic interaction.

Bridging two worlds: (DABCO-H)CuKI3 a hybrid copper iodide phosphor with a perovskite structure

Abstract A novel copper iodide hybrid compound, (DABCO-H)CuKI3, featuring a perovskite structure is here reported. Characterization techniques, including single crystal X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and photoluminescence studies, elucidate the structural and luminescent properties. The compound exhibits blue phosphorescence, attributed to mixed metal-to-ligand and halide-to-ligand charge transfer transitions, as supported by density functional theory (DFT) calculations and XPS valence band analysis. Furthermore, (DABCO-H)CuKI3 displays a remarkable adsorption capacity towards methylene blue dye. Kinetic modelling reveals that both film and intra-particle diffusion processes contribute to the adsorption rate.