Thermochromism In Solution Research Articles

Mononuclear copper(II) complexes containing chelating ligand of 2-methyl-N-(pyridine-2-yl-methyl)propane-2-amine as chromotropic probes

The synthesis of two mononuclear copper(II) complexes of formula [L2CuX]X where L is a bidentate ligand of N-(pyridin-2-yl-methyl)propane-2-amine and X = Cl, 1 and Br, 2, is reported. Both complexes are fully characterized by elemental analysis, spectroscopic techniques (IR, UV–Vis, and EPR), thermal analysis, conductance measurements, and single-crystal X-ray structure determination. The structures of both complexes are similar and display a distorted square–pyramidal arrangement around copper(II) ion. The chromotropism behavior of the complexes, including thermo- and halochromism, was investigated. The complexes demonstrated strongly pronounced reversible thermochromism in solution due to dissociation and re-coordination of halide and bidentate ligands. Their halochromism was investigated in pH range of 3.0–11.0 by visible absorption spectroscopy. Their reversible color variations from blue to colorless attributed to the deprotonation and protonation of the bidentate ligands.

Chromotropism studies on copper(II) compounds. Part II. Dinuclear copper(II) complexes with triply-bridged hydroxo, acetate, and halo ligands

Two triply-bridged dinuclear copper(II) complexes of formula [LCu(μ-OH)(μ-OAc)(μ-X)CuL]X⋅0.5H2O where L is a bidentate ligand of N-(pyridine-2-ylmethyl)propane-2-amine and X=Cl, 1 and Br, 2 were synthesized and characterized by elemental analyses, spectroscopic techniques (IR, UV–Vis, EPR), thermal analysis, conductance measurements, and single-crystal X-ray structure determination. The structures of both complexes are similar. The complexes show a distorted square-pyramidal arrangement around each copper(II) ion with a CuN2O2X chromophore in which both copper(II) ions are connected by a hydroxo bridge and a triatomic syn-syn carboxylato bridge in equatorial positions and a halide ion bridge at the axial site. The chromotropism behavior of the complexes, including solvato-, thermo-, and halochromism, were investigated in detail. Their halochromism was investigated in the pH range of 2.0–11.0 by visible absorption spectroscopy. The reversible color variations from blue to colorless are attributable to deprotonation and protonation of the ligands. The complexes show reversible thermochromism in solution due to dissociation and recombination of ligands to copper ions.

Solvato- and thermochromism study in oxalato-bridged dinuclear copper(II) complexes of bidentate diamine ligands

Two new oxalato complexes of the formula [Cu2(L)2(µ-ox)(MeOH)2](ClO4)2 (1) and [Cu2(L)2(µ-ox)](NO3)2 (2), where ox=oxalato and L=N,N′-dibenzylethane-1,2-diamine, were prepared and characterized by elemental analysis, IR and UV–vis spectroscopies and molar conductance measurements. The crystal structure of compound 1 was determined by single-crystal X-ray analysis. The compounds are solvatochromic and their solvatochromism was studied with different solvent parameter models using the stepwise multiple linear regression (SMLR) method with SPSS/PC software. It was demonstrated that the donor power of the solvent plays the most important role in the observed positive solvatochromism of the compounds. The complexes show irreversible thermochromism in solution due to the substitution of the weakly coordinated counter ions and coordinated solvents by solvent molecules.

Chromotropism in halo-bridged dimers. Structural characterization of bis(μ-halo)bis(halo N-(pyridin-2-ylmethyl)cyclohexanamine copper(II))

Two dinuclear copper(II) complexes, [LCu(μ-Cl)Cl]2 (DMF) (1) and [LCu(μ-Br)Br]2 (2), with the bidentate ligand N-(pyridin-2-ylmethyl)cyclohexanamine, L, were synthesized and characterized by physicochemical and spectroscopic (IR, UV–vis) data. The crystal structural analysis of 1 shows that both copper(II) ions are in a distorted square pyramidal N2Cl3 environment with the apical position of the copper(II) being occupied by the bridging chloride anion which is equatorial to the other copper ion, forming a dimeric copper(II) complex. The chromotropic properties of both complexes, including solvato-, thermo-, and halochromism, were investigated. The complexes show reversible thermochromism in solution which is irreversible in the solid state. It was found that the solvatochromism is due to structural change followed by solvation of the vacant sites of the complexes. Their halochromic properties were studied in pH range of 1–11 by visible absorption spectroscopy. The color changes from blue to green and to colorless are due to deprotonation and protonation of the ligands.

Structure and chromotropism properties of an unsymmetrical alkoxo-bridged nickel(II) cubane-like complex

A new tetranuclear cubane-like complex, [Ni4(L)4Cl4(H2O)3(EtOH)]·(H2O), has been synthesized from the reaction of a metal salt with the bidentate ligand 2-hydroxymethylpyridine (LH), and its crystal structure, spectroscopic and chromotropic properties have been studied. The complex has a [Ni4O4] core comprising a distorted cubane arrangement, of which four nickel(II) ions were bridged by μ3-alkoxo moieties. Each nickel(II) was coordinated to three μ3-alkoxo oxygens, one pyridine nitrogen and one chloride. The peripheral ligation was completed by an oxygen atom of water or ethanol ligand, which participated in intramolecular hydrogen bonding. Chromotropism properties of the complex including solvato-, thermo-, and ionochromism were investigated. The complex displayed strong ionochromism and shows high-sensitive and selective activity toward CN− and SCN− anions in the presence of other halides and pseudo-halides. The solvatochromic property of the complex was analyzed by a multi-parametric equation using SPSS/PC software. The stepwise multiple linear regression method demonstrated that the acceptor power of the solvent plays the most important role in the observed negative solvatochromism of the compound. It shows reversible thermochromism in solution due to loss of the weakly coordinated water and ethanol from the nickel(II) units.

Synthesis, structural characterization and chromotropism of a copper(II) complex containing a bidentate ligand

A new coordination compound, [Cu(L)2(OH2)](ClO4)2 where L=N-(pyridin-2-ylmethyl)propane-2-amine, was prepared and characterized by elemental analysis, molar conductance and IR and UV–Vis spectroscopic techniques. X-ray crystal analysis of the complex confirmed that the copper(II) ion has a distorted square pyramidal environment. The complex is chromotropic in solution. The chromotropic properties of the complex, including solvato-, thermo-, halo- and ionochromism, were investigated in detail. The complex displayed strongly pronounced reversible thermochromism in solution due to dissociation and of re-coordination of a water molecule.

Nickel(II) complexes with tetradentate N4 ligands: Synthesis, structure, electrochemistry and thermochromism in solution

Complexes of nickel(II) chloride with homologous tetradentate aminopyridine ligands 1,8-bis(2-pyridyl)-3,6-dimethyl-3,6-diazaoctane (pdao) and 1,6-bis(2-pyridyl)-2,5-dimethyl-2,5-diazahexane (bpmen) were prepared in the crystalline state and characterized by elemental analysis and X-ray diffraction as [Ni(pdao)(H2O)2]Cl2·H2O (1) and [Ni(bpmen)Cl2]·H2O (2). In the solid state, both complexes are blue-green and contain octahedral Ni(II) with a cis-α-coordinated tetramine. In aqueous solution, both complexes are strong electrolytes as follows from the measurements of electrical conductivity: complex 2 is hydrated and forms purple [Ni(bpmen)(H2O)2]2+(aq). Complex 1 displays thermochromic behavior in solution (it is blue-green at low temperatures and yellow at high temperatures) due to a temperature sensitive equilibrium [Ni(pdao)(H2O)2]2+(aq)⇄[Ni(pdao)]2+(aq)+2H2O(l), ΔH°=+30(1)kJ/mol and ΔS°=+80(3)J/molK in 0.1M NaClO4(aq). Complex 1, but not 2, can be reversibly reduced to the Ni(I) species (E1/2=−0.9V versus SHE in aqueous solution and −1.37V versus Fc+/Fc in acetonitrile). The relative stabilization of nickel(I) by ligand pdao can be attributed to an optimal size of the ligand bite and to the presence of the pyridine and tertiary amine N-donors.

Pyromellitic Diimide-Based Donor–Acceptor Poly(phenylene ethynylene)s

A series of donor–acceptor poly(phenylene ethynylene)s (PPEs) with N,N′-dialkylpyromellitic diimide (PMDI) as electron acceptor and various donor units are reported. Optoelectronic properties were investigated by UV/vis absorption and electrochemical measurements, revealing constant LUMO energies (∼−3.6 eV) across the series with HOMO energy levels governed by the donor monomers and optical band gaps from 2.30 to 1.50 eV. With a high volume fraction of solubilizing side chains, the polymers are soluble in common organic solvents, but solution NMR measurements and thermochromism in solution indicate aggregation due to additive intermolecular interactions between donor and acceptor units.

A New Class of Organosoluble Rigid-Rod, Fully Aromatic Poly(1,3,4-oxadiazole)s and Their Solid-State Properties, 2. Solid-State Properties

New symmetrical and unsymmetrical dialkoxy-substituted aromatic poly(1,3,4-oxadiazole)s are investigated by cyclovoltammetric measurements. The electrochemical redox behaviour of these materials is compared with the chemical structure. The reduction behaviour allows the estimation of the electron affinity, and shows that these polymers are suitable candidates for electron-transport materials in electronic devices. Surprisingly it is found from UV-vis and fluorescence spectroscopic measurements that the polyoxadiazole with linear alkoxy side chains (C16) shows a reversible thermochromism in solution as well as in the solid state. The changes in this temperature range are ascribed to a phase transition between aggregated chains, in solution as well as in the film, at room temperature and molecularly dissolved polymer chains at higher temperature. The other poly(1,3,4 oxadiazole)s with branched alkoxy side chains exhibit an improved solubility and they are completely soluble in odichlorobenzene at room temperature. The absorption and emission behaviour does not change in the temperature range from 25 °C to 100 °C. The fluorescence excitation studies of these poly(1,3,4-oxadiazole)s show a blue emission in solution and in the film. Due to these results the poly(1,3,4-oxadiazole)s are used as electron transport and blue emitting layers in electronic devices like diodes or polymer light emitting diodes (PLED).

Photoluminescence studies of solution thermochromism in a cyano-subsituted phenylene vinylene derivative

Time-resolved and steady-state photoluminescence (PL) studies of a cyano-substituted poly(phenylene vinylene) (CNPPV) in toluene solution are reported as a function of temperature. On reducing temperature there is no evidence for the formation of aggregates, with both the absorption and emission properties revealing only a moderate increase in the average length of conjugation. Time-resolved anisotropy data reveal a single rotational correlation time of six nanoseconds. These data are consistent with a very low molecular weight polymer sample that behaves in a molecular fashion.

Structural, Photophysical, and Conductive Properties of n-Hexyl Substituted Hybrid Polysilylene−Polysilyne Networks

Structural, photophysical, and charge transport properties of n-hexyl substituted polysilylenes containing 5, 33 or 67% n-hexylsilyne branching points were investigated. According to WAXD, DSC, and vibrational studies, introduction of branching points partially reduces the high degree of crystallinity of linear poly(di-n-hexylsilylene). A thermal transition occurs in all polymers, which leads to solid state thermochromic behavior. Solution thermochromism is also observed. It is shown that in the partially branched polymers the narrow band gap of polysilynes is accompanied by an exciton delocalization approaching that of linear polysilylenes. In the solid state, charge carrier mobilities, determined with the pulse-radiolysis time-resolved microwave conductivity technique, are high but decrease with increasing branching. They range from 1.5 × 10-5 for the linear polymer to 7.6 × 10-7 m2 V-1 s-1 for the polymer with 67% branching sites. At the thermal transition an abrupt drop in the mobility is observed, of which the magnitude decreases with increasing branching. The branching points appear to act as scattering points for both exciton and charge carrier migration.

SPIN STATE EQUILIBRIUM OF IRON(III) COMPLEX WITH PLANAR UNSYMMETRICAL QUADRIDENTATE SCHIFF BASE IN SOLUTION

Abstract New iron(III) complex containing planar unsymmetrical quadridentate Schiff base, [FeIm2L]Bφ4, showed a striking thermochromism in solution, changing from dark red to green with decrease of the temperature, where Im, L, and Bφ4 denote imidazole, N-hydroxyacetophenone-N′-acetylacetone-ethylenediimine, tetraphenylborate, respectively. The electronic and ESR spectra established that the thermochromism is caused by the spin equilibrium between high spin(S=5/2) and low spin(S=1/2) of iron(III).

Spectral investigation of the thermochromism of solutions of 1-benzothiazolyl-and 1-thiazolyl-5-p-nitrophenylformazans at low temperatures

Spectral investigation of the thermochromism of solutions of 1-benzothiazolyl-and 1-thiazolyl-5-p-nitrophenylformazans at low temperatures