Fluorescence Properties and Electrochemical Behavior of Some Schiff Bases Derived from N-Aminopyrimidine

A series of Schiff bases (L ₁ , L ₂ and L ₃ ) were prepared by refluxing aromatic aldehydes with N-Aminopyrimidine derivatives in methanol and ethanol. The structures of synthesized compounds were characterized by FTIR, ¹H NMR, ¹³C NMR and microanalysis. The electrochemical behaviors of the Schiff base ligands were also discussed. Moreover, the evaluation of absorption and emission properties of the structures were carried out in five different solvents. The products show visible absorption maxima in the range of 304–576 nm, and emission maxima from 636 to 736 nm in all solvents tested.     

Spectroscopic studies on the luminescence properties of ternary europium complexes with different ligands

In this paper, ligand effect of several bi-dental oxygen (O) and nitrogen (N) ligands on the red luminescence properties of europium ion (Eu³⁺) was studied comprehensively. Absorption, emission, and excitation spectral properties of ternary europium complexes with different combinations of ligands including thenoyl trifluoroacetone (TTA), naphthyl trifluoroacetone (NTA), 2,2′-bipyridyl (bpy) and phenanthroline (Phen) were investigated. Efficient Eu³⁺ red emission was observed with all the combinations of the above mentioned ligands. The most intense emission was found with the all nitrogen coordinated complex Eu(bpy)₂(Phen)₂ while the longest wavelength excitation band was recorded with oxygen-nitrogen mixed NTA-bpy complex Eu(NTA)₁(bpy)₃. With change of the ligands combination and ratio, the Eu³⁺ emission peak changes slightly from 612 to 618 nm. The absorption and excitation spectra of the europium complexes were compared and analyzed referring to the individual absorption spectral properties of the ligands. The relation between ligand-to-metal charge transfer states and luminescence intensities for different complexes was studied.     

Effect of symmetric substitution on the phenyl groups of Eu-dibenzoyl methane complexes on their luminescence properties

Complexes of Eu³⁺ ion and ligands like dibenzoylmethane (DBM) as well as flouro- and methoxy-substituted DBMs have been prepared and characterized. Peak maxima and line shapes of the π-π^* transitions arising from the ligands in these complexes were very sensitive to the nature of the substituents attached to the phenyl groups of DBM. Symmetric substitution at both the phenyl groups led to improved luminescence in terms of higher quantum yields of emission and longer lifetime of the excited state (⁵D₀) of Eu³⁺ ions. Effective averaging/cancellation of the dipole-dipole interactions in symmetrically substituted ligands and the associated decrease in the extent of quenching were responsible for the improved luminescence from such complexes.     

Photoluminescence, optical absorption and hypersensitivity in mono- and dinuclear lanthanide (Tb and Ho) β-diketonate complexes with diimines and bis-diimine bridging ligand

The photoluminescence properties of three Tb(III) complexes of the form [Tb₂(fod)₆(μ-bpm)], [Tb(fod)₃(phen)] and [Tb(fod)₃(bpy)] and optical absorption properties of their Ho(III) analogues (fod=anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, bpm=2,2′-bipyrimidine, phen=1,10-phenanthroline and bpy=2,2′-bipyridyl) in a series of solvents are presented. The luminescence of the complexes is sensitive to changes in environment (ligand/solvent) around Tb(III) and co-sensitization of the ancillary ligands. The enhancement of the luminescence intensity in coordinating solvents is attributed to the transformation of eight-coordination into less symmetric nine-coordination structure around Tb(III). Among phen and bpy, the phen is better co-sensitizer while bpm has been observed as poor co-sensitizer. The enhancement of the oscillator strength of ⁵G₆←⁵I₈ hypersensitive transition in the 4f-4f absorption in some coordinating solvents is attributed to decrease in the symmetry of the field around Ho(III) ion. The [Ho(fod)₃(phen)] is inert towards the solvents and retains its bulk structure and composition in solution. The transformation of the holmium complexes in DMSO into [Ho(fod)₃(DMSO)₂] species is found. The results reveal that the luminescence and 4f-4f absorption properties of lanthanide complexes in solution can be modulated by tuning the coordination structure through ancillary ligands and donor solvents.     

Synthesis of a Novel Fluorescent Schiff Base as a Possible Cu(II) Ion Selective Sensor

In this study a new fluorescent Schiff base; 1,1′-(4,4′-oxybis(4,1-phenylene)bis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)dinaphthalen-2-ol (2-HNA) was synthesized and characterized by FT-IR, UV-vis, and ¹H and ¹³C-NMR techniques. Photoluminescent properties of 2-HNA were investigated in different solvents including methanol, THF, DMF, DMSO, acetone, acetonitrile, and dichloromethane. 2-HNA was found to have higher emission intensity and Stoke’s shift value (∆λ_ST) in methanol solution. Relative emission intensity changes (I₀−I/I₀) of 2-HNA in methanol/water mixtures depending on different Cu⁺² ion concentrations were determined and a linearized plot was obtained. Possible interference of some other transition metal ions was also determined. Sensitivity limit of the new sensor was found to be higher than 5 × 10⁻⁷ mol/L. 2-HNA has quite high selectivity against Cu⁺² ion and, thus, can be used as a new fluorescence Cu⁺² ion sensor in practice.     

Hypersensitivity in the Luminescence and 4f?C4f Absorption Properties of Mono- and Dinuclear EuIII and ErIII Complexes Based on Fluorinated ??-Diketone and Diimine/ Bis-Diimine Ligands

The results of our investigation on the sensitized luminescence properties of three Eu(III) ??-diketonate complexes of the form [Eu₂(fod)₆(??-bpm)], [Eu(fod)₃(phen)] and [Eu(fod)₃(bpy)] and 4f?C4f absorption properties of their Er(III) analogues ( fod = anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione, bpm = 2,2??-bipyrimidine, phen = 1,10-phenanthroline and bpy = 2,2??-bipyridyl) in a series of non-aqueous solvents are presented. The Eu(III) complexes are highly luminescent and their luminescence properties (intensity and band shape) are sensitive to the changes in the inner coordination sphere of the Eu(III) ion. The luminescence intensity of the mononuclear complexes in pyridine is drastically decreased. The coordination structure of the complexes in pyridine is transformed into a more symmetrical one which results into a slow radiative rate of the emission from the complexes. The ancillary ligands, phen and bpy are found better co-sensitizers as compared to the bpm to sensitize Eu(III)-luminescence. The 4f?C4f absorption properties (oscillator strength and band shape) of the Er(III) complexes demonstrate that ⁴G_11/2 ?? ⁴I_11/2 and ²H_11/2 ?? ⁴I_15/2 hypersensitive transitions of Er(III) are very sensitive in some coordinating solvents which reflects complex?Csolvent interaction in solution. The hypersensitive transitions of [Er(fod)₃(phen)] remain unaffected in any of the solvents and this complex retains its bulk composition in solution. The erbium complexes as well as the Er(fod)₃ chelate are invaded by DMSO. This solvent enters the inner coordination sphere by replacing heterocyclic ligand and the complexes acquire similar structure [Er(fod)₃(DMSO)₂] in this solvent. The results reveal that the luminescence and absorption properties of lanthanide complexes in solution can be controlled by tuning the coordination structure through ancillary ligands and donor solvents. This work shall prove useful in designing new biological applications with such probes.     

Synthesis and Fluorescence Properties of Eu<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript> Complexes with Schiff Base Derivatives

Novel Schiff base ligands derived from N′-benzylidene-benzohydrazide (substituted by –H, ?CH₃, ?OCH₃, ?Cl) and 2-chloro-N-phenylacetamide were synthesized. The solid complexes of rare earth (Eu, Tb) nitrate with these Schiff base ligands were synthesized and characterized by elemental analysis, EDTA titrimetric analysis, thermal analysis, infrared spectra and UV–Vis spectra analysis. The fluorescence properties of rare earth (Eu, Tb) complexes in solid were studied. Under the excitation of ultraviolet light, these complexes exhibited characteristic emission of europium and terbium ions. The results showed that the ligand favored energy transfer to the emitting energy of Eu and Tb ions. Effects of different ligands on the fluorescence intensity of rare earth (Eu, Tb) complexes had been discussed. The electrochemical properties of rare earth (Eu, Tb) complexes were also investigated.     

Synthesis and Spectroscopic Studies of Some New Polyether Ligands of the Schiff Base Type

Abstract

New polyether ligands of Schiff base type (3–13) were synthesized from the reaction of diethylene glycol bis(2‐aminophenyl)ether and triethylene glycol bis(2‐aminophenyl)ether with salicylaldehyde, 5‐methoxysalicylaldehyde, 5‐bromosalicylaldehyde, 5‐nitro salicylaldehyde, and 2‐hydroxy‐1‐naphthaldehyde. The products were characterized by elemental analysis, IR, ¹H, ¹³C NMR, and UV‐VIS techniques. The UV‐VIS spectra of those Schiff bases with an OH group in the ortho position to the imino group were studied in polar and nonpolar solvents in acidic and basic media. The compounds are in tautomeric equilibrium (enol‐imine, O–H · N?keto‐amine, O · H–N forms) in solvents, acidic chloroform, and benzene solutions and basic DMSO, chloroform, and benzene solutions. These tautomers were not observed in polar and non‐polar solvents and in basic solutions of DMSO, chloroform, and benzene for the Schiff bases 5–10. Tautomer proportions, which were obtained from ¹H NMR and UV‐VIS data in DMSO, were compared for compounds 3, 4, 11, and 12.     

Design,Synthesis, Photophysical Properties,Biological Estimation and Molecular Docking Studies of Novel Schiff Base Derivatives as Potential Urease Inhibitors

A quinoline functionalized two novel fluorescent Schiff bases, N-(quinolin-2-ylmethylene) anthracen-1-amine (SB1) and 2-(quinolin-2-ylmethyleneamino) benzene thiol (SB2) were synthesized and confirmed by using ¹H NMR, IR and GC-MS techniques. The spectroscopic properties were examined by absorption spectroscopy and fluorescence spectroscopy. The absorption and fluorescence spectra of the probes (SB1 and SB2) were measured in a variety of solvents. Both the compounds were tested for urease inhibitory activity. The synthesized compound SB2 proved to be the most effective screening for enzyme inhibitory activity with IC₅₀?=?0.111 μM than SB1 (IC₅₀?=?0.287 μM). Molecular docking studies were performed to delineate the binding affinity and conformational positions of chemical compounds within the active region of the target protein. In-vitro analysis depicts the potency of SB1 in free radical scavenging as compared to the reference drug vitamin C.     

Synthesis,spectroscopic, thermal and electrical conductivity studies of three charge transfer complexes formed between 1,3-di[(<Emphasis Type="Italic">E</Emphasis>)-1-(2-hydroxyphenyl)methylideneamino]-2-propanol Schiff base and different acceptors

Charge-transfer complexes (CTC) resulting from interactions of 1,3-di[(E)-1-(2-hydroxyphenyl) methylideneamino]-2-propanol Schiff base with some acceptors such as iodine (I₂), bromine (Br2), and picric acid (PiA) have been isolated in the solid state in a chloroform solvent at room temperature. Based on elemental analysis, UV-Vis, infrared, and ¹H NMR spectra, and thermogravimetric analysis (TG/DTG) of the solid CTC, [(Schiff)(I₂)] (1), [(Schiff)(Br₂)] complexes with a ratio of 1:1 and [(Schiff)(PiA)₃] complexes with 1:3 have been prepared. In the picric acid complex, infrared and ¹H NMR spectroscopic data indicate that the charge-transfer interaction is associated with a hydrogen bonding, whereas the iodine and bromine complexes were interpreted in terms of the formation of dative ion pairs [Schiff⁺, I₂^∙−] and [Schiff⁺, Br₂^∙−], respectively. Kinetic parameters were obtained for each stage of thermal degradation of the CT complexes using Coats–Redfern and Horowitz–Metzger methods. DC electrical properties as a function of temperature of these charge transfer complexes have been studied.     

Phosphorescent iridium(III) complexes with hetero (C ˆN) ligands

In order to improve luminescence efficiency, it is necessary to design a phosphorescent material which is capable of transferring the excited energy without triplet–triplet (T–T) annihilation. For this purpose, new types of metal complexes were designed with different species of (C ˆN) ligands. Herein, Ir(ppy)₂(piq), Ir(ppy)₂(piq-F) and Ir(ppy)₂(piq-CF₃) were designed and prepared, where ppy, piq, piq-F and piq-CF₃ represent 2-phenylpyridine, 1-(phenyl)isoquinoline, 1-(4′-fluorophenyl)isoquinoline and 1-(4′-trifluoromethylphenyl)isoquinoline, respectively. These Ir(III) complexes having two different ligands (hetero-Ir complexes) are expected to have a high luminescence efficiency by intramolecular energy transfer from the energy absorbing ligand to the luminescent ligand leading to a decrease in quenching or energy deactivation. To compare luminescent characteristics of these hetero-Ir complexes, homo-Ir complexes Ir(ppy)₃, Ir(piq)₃, Ir(piq-F)₃ and Ir(piq-CF₃)₃ were prepared and investigated photophysically.     

Comparison of the ht Ultraviolet-Visible Spectra of the Copper(Ii) Complexes of Bidentate Schiff Base Ligands

Abstract

The bis(salicylaldiminato)copper(II) complexes of the ligand series of salicylaldimines derived from the condensation of n-alkyl or n-alkyloxy substituted aromatic amines with 2,4-dihydroxybenzaldehyde were synthesized. a series of Schiff base ligands with the general formula 4-X-N-(2,4-dihydroxybenzylidene)-aniline and differing only in substituents were synthesized. Some of these compounds have already been reported in literature. X=OCH₃[1],OC₂H₅[2],C₄H₉[1]. the copper(II) complexes of these ligands having the general formula, copper, bis[o-[N-(p-X-phenyl) formimidoyl]-4-hydroxyphenolato] were also synthesized. the ligands and their complexes, a total of 24 in number, are studied systematically with ultraviolet-visible spectroscopy to examine the effect of various n-alkyl- and n-alkyloxy substituents on the ligands and on their complexes. in the electronic spectrum of these compounds, the bands observed in the 200-450 run region which involve charge transfer π-π? transition were interpreted.     

Spectrophotometric Studies of the Influence of Organic Solvents and Substituents on Some Schiff Bases

The effect of the substituents, solvent polarities and hydrogen ion concentration on the electronic structure and UV/VIS absorption spectra of some Schiff bases, derivatives of N-(R-benzylidene)benzidine (R = o-NO₂ and o-OH, p-OH) and N-(R-furfurylidene)benzidine (R = H and 5 - NO₂), have been studied. The spectral shifts obtained in various organic solvents were discussed on the basis of the specific solute - solvent interactions through the formation of hydrogen bonds between hydrogen-bond donor (HBD) solvents and the benzidine nitrogen atom of the Schiff bases. Some interpretations of the electronic aspects of this type of hydrogen bonding were discussed as well as the stabilization effects due to the solvation. Finally, the pK values of the compounds were determined.     

Excitation energy dependent chromaticity of BaZr(BO3)2:Eu

The luminescence properties of BaZr(BO₃)₂:5% Eu were investigated under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation and different luminescence behaviors were observed by different excitation energies. After the analyses of the luminescence spectra, the result indicates that Eu³⁺ occupying non-centrosymmetric sites Ba²⁺ can be excited preferentially under 254 nm excitation, while Eu³⁺ occupying centrosymmetric sites Zr⁴⁺ can be excited preferentially under 147 nm excitation.     

Magnetic and optical properties of nitroxide radicals and their lanthanide complexes

This paper reports the structural, magnetic and optical properties of three series of lanthanide complexes [Ln(radical)₄](ClO₄)₃, [Ln(radical)₂(NO₃)₃] and [Ln(radical)(hfac)₃] (Ln=Gd(III), La(III) or Eu(III)) with nitronyl or imino nitroxide radicals.The magnetic properties of the gadolinium complexes were studied. Along the series, most gadolinium(III) complexes exhibit antiferromagnetic Gd^III-radical interaction. These results are discussed.The full absorption and luminescence spectra of some lanthanide complexes and their uncoordinated free radical ligands were measured. The rich vibronic structure in luminescence and absorption spectra indicates that several excited states define the absorption spectra between 400 and 800 nm. Qualitative trends can be established between magnetic ground state properties and the energies and vibronic structure of the title compounds.     

Intramolecular Energy Transfer and Co-luminescence Effect in Rare Earth Ions (La, Y, Gd and Tb) Doped with Eu3+ β-diketone Complexes

In this paper, Eu³⁺ β-diketone Complexes with the two ligands 1-(2-naphthoyl)-3, 3, 3-trifluoroacetonate (TFNB) and 2’2-bipyridine (bpy) have been synthesized. Furthermore, we reported a systematical study of the co-fluorescence effect of Eu(TFNB)₃bpy doped with inert rare earth ions (La³⁺, Gd³⁺ and Y³⁺) and luminescence ion Tb³⁺. The co-luminescence effect can be found by studying the luminescence spectra of the doped complexes, which means that the existence of the other rare earth ions (La³⁺, Y³⁺, Gd³⁺ and Tb³⁺) can enhance the luminescence intensity of the central Eu³⁺, which may be due to the intramolecular energy transfer between rare earth ions and Eu³⁺. The efficient intramolecular energy transfer in all the complexes mainly occurs between the ligand TFNB and the central Eu³⁺. Full characterization and detail studies of luminescence properties of all these synthesized materials were investigated in relation to co-fluorescence effect between the central Eu³⁺ and other inert ions. Further investigation into the luminescence properties of all the complexes show that the characteristic luminescence of the corresponding Eu³⁺ through the intramolecular energy transfers from the ligand to the central Eu³⁺. Meantime, the differences in luminescence intensity of the ⁵D₀→⁷F₂ transition, in the ⁵D₀ lifetimes and in the ⁵D₀ luminescence quantum efficiency among all the synthesized materials confirm that the doped complex Eu_0.5Tb_0.5(TFNB)₃bpy exhibits higher ⁵D₀ luminescence quantum efficiency and longer lifetime than the pure Eu(TFNB)₃bpy complex and other materials.     

Spectroscopic Characterization of Oxime Ligands and Their Complexes

New imine–oxime ligands H₃L¹–H₃L³ have been obtained from reactions of the Schiff base ligands H₂B¹–H₂B³ with monochloroglyoxime. Mononuclear copper(II), cobalt(II), nickel(II), vanadyl(IV) and zinc(II) complexes of the imine–oxime ligands H₃L¹–H₃L³ have been prepared and characterized by elemental analyses, infrared and electronic spectra, magnetic moment and molar conductance data. The molar conductance data show that the complexes are non‐electrolytes. When the imine–oxime ligands react with the metal salts in a 2:1 ratio, they behave as dibasic bidentate ligands towards one metal ion. The nickel(II) and zinc(II) complexes are diamagnetic. The ¹H(¹³C)‐nmr spectra of all ligands and nickel(II) and zinc(II) complexes of the ligands H₃L¹–H₃L³ have been recorded. Mass spectra of the imine–oxime ligands and their nickel(II) and zinc(II) complexes were recorded. Some of the ligands and metal complexes have antibacterial activity.     

The luminescence properties of Eu2+ doped Na2CaMg(PO4)2 phosphor

The blue-emitting phosphors of Eu²⁺-doped Na₂CaMg(PO₄)₂ were prepared by high-temperature solid-state reaction. The crystal phase formation was confirmed by X-ray powder diffraction measurement. The luminescence properties were investigated by photoluminescence excitation and emission spectra. The phosphor exhibited the blue luminescence due to the 4f⁶5d¹→4f⁷ transition of Eu²⁺ ions under the excitation of near UV light. The influence of temperature on the luminescence intensities and decay lifetimes of Eu²⁺ was investigated. An unusual increase of the decay lifetimes of the 4f⁶5d emission of Eu²⁺ ion is observed in Na₂CaMg(PO₄)₂ from 10 K to room temperature. The thermal stability of the luminescence of Eu²⁺-doped Na₂CaMg(PO₄)₂ was discussed.     

Applicability of Reddish-Orange Light Emitting Samarium (III) Complexes for Biomedical and Multifunctional Optoelectronic Devices

Six crimson samarium (III) complexes based on β-ketone carboxylic acid and ancillary ligands were synthesized by adopting the grinding technique. All synthesized complexes were investigated via elemental analysis, infrared, UV–Vis, NMR, TG/DTG and photoluminescence studies. Optical properties of these photostimulated samarium (III) complexes exhibit reddish-orange luminescence due to ⁴G_5/2?→?⁶H_7/2 electronic transition at 606 nm of samarium (III) ions. Further, energy bandgap, color purity, CIE color coordinates, CCT and quantum yield of all complexes were determined accurately. Replacement of water molecules by ancillary ligands enriched these complexes (S2-S6) with decay time, quantum yield, luminescence, energy bandgap and biological properties than parent complex (S1). Interestingly, these efficient properties of complexes may find their applications in optoelectronics and lighting systems. In addition to these, the antioxidant and antimicrobial assays were also investigated to explore the applications in biological assays.