Mihaela Homocianu

Optical properties of some new azo photoisomerizable bismaleimide derivatives.

Novel polythioetherimides bearing azobenzene moieties were synthesized from azobismaleimides and bis-2-mercaptoethylether. Kinetics of trans-cis photoisomerization and of thermal conversion of cis to trans isomeric forms were investigated in both polymer solution and poly(methyl methacrylate) doped films using electronic absorption spectroscopy. Thermal recovery kinetics is well described by a two-exponential relation both in solution and polymer matrix, while that of low molecular weight azobismaleimide fit a first-order equation. The photoinduced cis-trans isomerization by visible light of azobenzene chromophores was examined in solution and in polymer films. The rate of photoinduced recovery was very high for azobismaleimides.

Solvatochromic effects in the UV/vis absorption spectra of some pyridazinium ylides.

Solvatochromic behavior of some carbanion monosubstituted and disubstituted pyridazinium ylides was studied experimentally in various polar and nonpolar solvents. Different solvent parameters, such as microscopic solvent polarity, E(T)(30), the Kamlet-Taft and the Catalan parameters have been used for describing the solute-solvent interactions and solvatochromic shifts of the visible intramolecular charge transfer (ICT) absorption band of pyridazinium ylides. It is found that the solute hydrogen bond donating ability and dipolarity/polarizability play an important role in the description of the pronounced solvatochromism in the studied solutions. The Catalan solvent scales are found to be the most suitable for describing the solvatochromic shifts.

Solvent effects on the photophysical properties of poly[1,4-dihydroxyanthraquinoneimine-1,3-bis(phenylene-ester-methylene)tetramethyldisiloxane]

Absorption and fluorescence spectra of a polyquinoneimine, PQI, built on 1,4-dihydroxyanthraquinone and a siloxane diamine, 1,3-bis(amino-phenylene-ester-methylene)tetramethyldisiloxane, have been investigated in solvents of different polarities. The effect of solvents on the spectral properties was investigated using Lippert-Mataga and Bakhshiev polarity functions and Cataláns multiple linear regression approach. Absorption and fluorescence spectra in studied solvents exhibit hypsochromic and bathochromic shifts, respectively. The polarity of the solvent was the main parameter which changes the spectral properties of PQI. Also, the binary mixtures of chloroform with methanol and dimethyl sulfoxide were used to analyze the intermolecular interactions and preferential solvation. The preferential solvation parameters (local mole fraction (X₂(L)), excess function (δs₂) and preferential solvation constant (KPS)) were calculated from spectral data and discussed as a function of cosolvent content. The values of quantum yield, decreased linearly with increasing solvent polarity (for non-polar and polar solvents).

Optical Properties of Some Fluorinated Poly(1,3,4-Oxadiazole-Ether)s in Homogeneous and Heterogeneous Media. Changes Induced by SnO2, NiO and SnO2/NiO Mixed-Oxide Nanoparticles

Optical characteristics of some fluorinated poly(1,3,4-oxadiazole-ether)s in presence of SnO2, NiO and SnO2/NiO mixed-oxide nanoparticles (NPs) was investigated. The interactions between polymers and metal oxide NPs were studied by steady-state UV-Vis absorption and fluorescence spectroscopy techniques. The absorption and fluorescence signals of all investigated polymers was modified by presence of both pure and mixed-oxide nanoparticles. The moderate values of Stern-Volmer quenching constant and non-linear trend of Scott plot indicate the less affinity between metal oxide NPs and polymers. The solvation behavior of some fluorinated poly(1,3,4-oxadiazole-ether)s in chloroform–N,N-dimethylformamide and N,N-dimethylformamide-dimethylsulfoxide mixtures was discussed.

Intermolecular interactions in binary solutions of some pyridazinium ylids studied by visible electron spectroscopy

Some pyridazinium ylids used as precursors in obtaining pulmonary active drugs were studied from the point of view of intermolecular interaction nature in different solvents. The solvatochromic effect in solvents with different physicalchemical properties was used to establish the nature of the intermolecular forces acting on the pyridazinium ylid molecules in binary solutions. In the aprotic solvents only universal interactions were emphasized, while in the protic ones a supplemental hypsochromic shift of the visible electronic band proves the existence of specific interactions. The supply of different kind of interactions in pyridazinium ylid solutions was also estimated.

Synthesis and photophysical study of new blue fluorescent poly(azomethine-1,3,4-oxadiazole)s containing dimethylamino groups:

New aromatic polyazomethines were synthesized by polycondensation reaction of a diamine containing 1,3,4-oxadiazole ring, namely, 4,4′-diamino-4″-[2-(4-phenoxy)-5-(4-dimethylaminophenyl)-1,3,4-oxadiazole)]triphenylmethane, with terephthalic aldehyde or bis(4-formylphenoxyphenyl)fluorene, by using N-methyl-2-pyrrolidinone (NMP) as solvent. The polymers were easily soluble in polar solvents, such as NMP, N,N-dimethylacetamide, or chloroform, and showed high thermal stability with the initial decomposition temperature above 415°C and the temperature of 10% weight loss in the range of 450–460°C. They exhibited high char yield at 800°C in the range of 52–56%. Optical properties were studied by absorption and photoluminescence spectra. In solution, the polymers presented two absorption maxima in the ranges 273–278 and 330–346 nm and emitted violet-blue light in the range of 413–468 nm, depending on the solvent polarity. The Stokes shift and emission quantum yield values depend on the polymer structure and solvent polarity. The emission intensity in NMP solution was enhanced upon increasing the HCl concentration, while the absorption spectral profile was slightly influenced.

1,3,4-Oxadiazole Derivatives. Optical Properties in Pure and Mixed Solvents.

Abstract1,3,4-Oxadiazole derivatives-organic materials are an interesting and continuously developing area of research. This review describes some optical properties and highlights the current applications of these compounds in biomedical and optoelectronic fields. The relationships between polymer structures, environmental factors and optical properties (absorption and fluorescence) of several selected and relevant l,3,4-oxadiazole-containing molecules were presented in this review. These aspects were analyzed in various pure solvents and microheterogeneous media (mixed solvents). Also, the selectivity and sensitivity of some 1,3,4-oxadiazole derivatives-organic materials for different metal ions were discussed and evaluated by using spectral techniques. Finally, some important photophysical characteristics of 34 series of organic materials containing −1,3,4-oxadiazole rings, were collected in a table.

New Thermoplastic Ionic Elastomers Based on MA-g-EPDM with Advanced Characteristics

a. Synthesis of elastomers containing ionizable monomers or just preparing the thermoplastic ionic elastomers on the same equipment where polymerization, copolymerization or polycondensation of the basic monomers in the polymer chain are performed, but adding small amounts (5-7%) of other monomers resulting in ionic or ionizable groups in the polymer chain. b. Converting chemically some elastomers containing double bonds in their macromolecules. c. Processing elastomers containing ionizable groups with metal salts, metal alkali or metal oxides which can react with the functional groups in the ionizable groups, thus yielding ionic ranges; fillers, ionic plasticizers, polyolefins, antioxidants etc. can be also added in order to obtain ionic thermoplastic elastomer compounds with a large variety of applications depending on their composition (Zuga, 2005).