Structure and Luminescent Properties of the 4-Arylidene-2-Aryl-5-Oxazolones(Azlactones)In Solution and Crystalline State

Experimental and theoretical evaluations have proven that very low fluorescence quantum yields of azlactones in solution are not caused by an efficient inter system crossing from S₁*(ππ) to T*(nπ) states, but rather from solvation and steric effects, that result in non-planarity of the molecular system. High fluorescence quantum yields in the solid state are attributed to the planarity of the azlactone molecule upon packing into the crystal lattice. Supporting evidence was found upon observation of the excited state proton transfer (ESIPT) bands of fluorescence emissions of o-hydroxyarylidene derivatives. The photoinstability of azlactones in liquid states are attributed to photochemical E-Z isomerization and cleavage of the hetero ring α to the carbonyl group.     

A closed-form expression for the Drinfeld modular polynomial Φ<Subscript><Emphasis Type="Italic">T</Emphasis></Subscript>(<Emphasis Type="Italic">X</Emphasis>, <Emphasis Type="Italic">Y</Emphasis>)

In this paper we give a closed-form expression for the Drinfeld modular polynomial \({\Phi_T(X,Y) \in \mathbb{F}_q(T)[X,Y]}\) for arbitrary q and prove a conjecture of Schweizer. A new identity involving the Catalan numbers plays a central role.     

Synthesis,Spectroscopic Characterization and Polymerization Abilities of Blue and Green Light Emitting Oxazol-5-one Fluorophores

New fluorescent thiophenyl group containing oxazol-5-one fluorophores of 3a (4-(3-thiophenylmethylene)-2-phenyloxazol-5-one), 3b (4-(3-thiophenylmethylene)-2-(4-tolyl)oxazol-5-one) and 3c (4-(3-thiophenylmethylene)-2-(4-nitrophenyl)oxazol-5-one) were synthesized and characterized. The newly synthesized oxazol-5-ones absorption and fluorescence characteristics were studied in some solvents of varying polarities. The heterocyclic chromophores were fluorescent, with two of them, 3a and 3b, emitting blue light, whilst the other one, 3c, emitting green light. The emission maxima of the derivatives varied between 415 and 572 nm according as the extent of conjugation and solvent polarity. As solvent polarity increased, 3c derivatives emission spectra displayed a large bathochromic shift, which revealed the considerable change of the dipole moment of the fluorescent structure because of an intramolecular charge transfer interaction. Furthermore, oxazolones polymerization ability via the thiophenyl group linked to the oxazol-5-one heterocycle showed that copolymerization of 3a was achieved, but homopolymerization was not observed.     

Metal Complexation Properties of Schiff Bases Containing 1,3,5-Triazine Derived from 2-Hydroxy-1-Naphthaldehyde in Solution. A Simple Spectrofluorimetric Method to Determine Mercury (II)

Four new Schiff base ligands carrying naphthalene groups were prepared from the reaction of 2,4-diamino-6-methyl-1,3,5-triazine and 2,4-diamino-6-undecyl-1,3,5-triazine with 2-hydroxy-1-naphthaldehyde. The influence of a series of metal ions including Cu²⁺, Co²⁺, Hg²⁺, Al³⁺, Cr³⁺, Fe³⁺, Pb²⁺, Ni²⁺, Cd²⁺, Zn²⁺, Mn²⁺, Ag⁺, Ba²⁺, Ca²⁺ and Mg²⁺ on the spectroscopic properties of the ligands was investigated by means of absorption and emission spectrometry. The results of spectrophotometric and spectrofluorimetric titrations disclosed the complexation stoichiometry and complex stability constant of the ligands with metal ions. A simple spectrofluorimetric method was developed using the Schiff base derived from 2,4-diamino-6-undecyl-1,3,5-triazine to determine Hg²⁺ ion. No cleanup or enrichment of the tap water sample was required. A modified standard addition method was used to eliminate matrix effect. The standard addition graph was linear between 0.2 and 2.6 mg/L in determination of Hg²⁺. Detection and quantification limits were 0.08 and 0.23 mg/L, respectively. The simple and cost-effective method can be applied to water samples.     

A theoretical study on calculation of absolute hydration enthalpies for some univalent ions

Using the total radius of alkaline fluorides and sodium halides and their experimental total enthalpy values, absolute hydration enthalpies of sodium and fluoride ions ( and ) were previously calculated. Also, by the help of data of sodium and fluoride ions for all alkaline metal ions and halides absolute hydration enthalpies were determined.

Polymer Composites for Thermoelectric Applications

This review covers recently reported polymer composites that show a thermoelectric (TE) effect and thus have potential application as thermoelectric generators and Peltier coolers. The growing need for CO₂‐minimizing energy sources and thermal management systems makes the development of new TE materials a key challenge for researchers across many fields, particularly in light of the scarcity or toxicity of traditional inorganic TE materials based on Te and Pb. Recent reports of composites with inorganic and organic additives in conjugated and insulating polymer matrices are covered, as well as the techniques needed to fully characterize their TE properties.     

Relaxation experiments with synchrotron radiation

Relaxation phenomena show up in standard energy domain Mössbauer spectra via line broadening. The evaluation of such spectra is in most cases done by adopting the stochastic theory mainly developed in the 60s and 70s. Due to the time structure and the polarization of the synchrotron radiation nuclear resonance forward scattering in the time domain gives valuable information on relaxation mechanisms. We report here mainly on Nuclear Forward Scattering (NFS) experiments investigating the paramagnetic relaxation of the Fe³⁺ ion in (NH)₄Al_0.95 ⁵⁷Fe_0.05(SO₄)₂·12H₂O and briefly on recent investigations on charge fluctuations in Eu₃S₄.     

Pure nuclear reflexes and combined hyperfine interactions in YIG

Mössbauer spectra of oriented YIG single crystals were taken and the numerical analysis using the transmission integral yielded a consistent set of hyperfine interaction parameters. They are in good agreement with theoretical values obtained by MO-calculations which included clusters up to 62 ions. Finally pure nuclear reflexes are predicted for single crystals and two theoretical spectra are given.Dedicated to U. Gonser on his 60. birthday