Effects of long-wavelength fluorescence excitation in N, N′-dimethylaminobenzonitrile liquid solutions

We have studied the properties of the emission, absorption, and excitation of dual fluorescence of N,N??-dimethylaminobenzonitrile in a set of solvents of different polarity under selective irradiation of solutions by light with different energies of quanta in the range of the long-wavelength absorption band. In all cases, dual fluorescence is observed, which is caused by emission from locally excited Franck-Condon and charge-transfer states. A change in the energy of excitation quanta has no effect on the position of the fluorescence bands; however, the intensity ratio between the bands noticeably changes in favor of the intensity of the long-wavelength band, which belongs to the charge-transfer state. To explain the observed effects, we involve data of quantum-mechanical calculations, which show that there is a considerable probability of occurrence in solutions of these systems of rotational isomers that differ in the orientation of the dimethylamino group with respect to benzonitrile. In the excited state, these rotamers have different charge-transfer reaction rates, which leads to a change in the intensity ratio of the observed fluorescence bands upon using the selective excitation.     

The influence of temperature on red-edge excitation effects in liquid solutions of N,N′-dimethylaminobenzonitrile

A systematic study of new photophysical and photochemical processes in solutions is continued by the example of a recently found phenomenon of redistribution of the intensities of two fluorescence bands of N,N′-Dimethylaminobenzonitrile (DMABN) in polar solutions at room temperatures under selective irradiation by light with different photon energies in the region of the long-wavelength absorption band. The effects observed are explained using data of quantum-mechanical calculations, which reveal that solutions of these systems are very likely to contain rotational isomers with different orientations of the dimethylamino group with respect to the plane of the benzonitrile residue. The excited-state charge transfer reactions in these rotamers occur in different ways and, hence, with different rates, because of which the intensity ratio of recorded fluorescence bands is different for different wavelengths of selective excitation. In this study, the influence of the temperature on the red-edge excitation effect observed in the fluorescence of DMABN solutions in acetonitrile is studied in the temperature range of 274–313 K using the previously used selective excitation method. It is found that these effects manifest themselves at any temperature within this range, but are especially strong at 313 K. The parameters of the dual fluorescence that are most sensitive for recording of the considered effects are determined, and the obtained temperature dependences are interpreted.     

ESR study on radiation chemical processes in polyvinyl alcohol films at 77°k

Abstract

Trapped electrons (e_t ^?) were detected in irradiated PVA films at 77°K. Yield of e_t ^? was decreased as evaporating water from the films, indicating that water molecules contribute to construct pre-existing traps in the polymer. The radical produced at 77°K was identified as a precursor of the radical produced at room temperature.     

Investigations on Fe doped polyvinyl alcohol films with and without gamma (γ)-irradiation

This paper deals with the preparation of pure and ferric chloride (FeCl₃) doped polyvinyl alcohol (PVA) films by solution casting method. Optical and electrical properties were systematically investigated. We have found the decrease in optical band gap energy of PVA films on doping FeCl₃. The optical band gap energy values in the present work are found to be 3.10 eV for pure PVA, 2 eV for PVA:Fe³⁺ (5 mol%), 1.91 eV for PVA:Fe³⁺(15 mol%) and 1.8 eV for PVA:Fe³⁺(25 mol%). Direct current electrical conductivity (σ) of pure, FeCl₃ doped PVA films in the temperature range 70-127 °C has been studied. At 387 K dc electrical conductivity of pure PVA film is 5.5795 μ Ω⁻¹ cm⁻¹, PVA:Fe³⁺ (5 mol%) film is 10.0936 μ Ω⁻¹ cm⁻¹ and γ-Irradiated PVA:Fe³⁺ (5 mol%) film for 900 CGY/min is 22.1950 μ Ω⁻¹ cm⁻¹. The result reveals the enhancement of the electrical conductivity with γ-irradiation. FT-IR study signifies the intermolecular hydrogen bonding between Fe³⁺ ions of FeCl₃ with OH group of PVA.     

Vibrational Spectroscopic and Theoretical Studies of Urea Derivatives with Biochemical Interest: N,N′-Dimethylurea,N,N,N′,N′-Tetramethylurea,and N,N′-Dimethylpropyleneurea

Abstract

Mid-infrared, far-infrared, and Raman vibrational spectroscopic studies were combined with density functional theory (DFT) calculations and normal coordinate force field analyses for N,N′-dimethylurea (DMU), N,N,N′,N′-tetramethylurea (TMU), and N,N′-dimethylpropyleneurea (DMPU: IUPAC name 1,3-dimethyltetrahydropyrimidin-2(1H)-one). The equilibrium molecular geometry of DMU (all three conformers), TMU, and DMPU and the frequencies, intensities, and depolarization ratios of their fundamental infrared (IR) and Raman vibrational transitions were obtained by DFT calculations. The vibrational spectra were fully analyzed by normal coordinate methods as well. A starting force field for DMPU was obtained by adapting corresponding force constants for DMU and TMU, resulting after refinements in the stretching force constants C=O (7.69, 7.30, 7.68 N·cm^?1), C–N (5.16, 5.55, 5.05 N·cm^?1), and C-Me (5.93, 4.00, 4.22 N·cm^?1) for DMU, TMU, and DMPU, respectively. The dominating conformer of liquid DMU was identified as trans-trans, strong intermolecular hydrogen bonding was verified in solid DMU, and weak dipole–dipole association was found in liquid TMU and in DMPU. Special attention was paid to analyzing the methyl group frequencies, which revealed deviations from local C_3v symmetry. A linear correlation was found between the CH stretching force constants and the inverse of the CH bond lengths (1/r ²). The averaged NH stretching frequencies of gaseous, dissolved, and solid urea and of DMU, with variations for hydrogen bonding of different strength, are linearly correlated to the NH stretching force constants. Characteristic skeletal vibrations were assigned for a broad variety of urea derivatives and also for pyrimidine derivatives, which all contain the N₂C=O entity. The very strong IR bands of C=O stretching (1,676 ± 40 cm^?1) and asymmetric CN₂ stretching (1,478 ± 60 cm^?1), and the very intense Raman feature of symmetric CN₂ stretching or ring breathing (757 ± 80 cm^?1), can be recognized as fingerprint bands also for the pyrimidine derivatives cytosine, thymine, and uracil, which all are nucleobases in DNA and RNA nucleotides.     

Modulation of charge transfer rate in (N,N′-dimethylamino)benzonitrile liquid solutions

We studied the properties of the emission, absorption and excitation of dual fluorescence of (N,N′?dimethylamino)benzonitrile in a polar aprotic solvent acetonitrile under selective irradiation of solutions by light with different energies of quanta to elucidate mechanisms of dual fluorescence arising in this solvent at different temperatures in the range 274–313 K. In all cases, dual fluorescence of the solute in acetonitrile was observed, which is caused by emission from locally excited Franck-Condon and charge-transfer states. A change in the energy of excitation quanta has a weak effect on the position of the fluorescence bands; however, the intensity ratio between the bands noticeably changes in favour of the intensity of the long-wavelength band at excitation in the range of the long-wavelength absorption band. An interesting and unusual fact is that solution heating is accompanied by essential growth of quantum yield of dual fluorescence at all wavelengths of the excitation. To explain the observed effects, the same dependences were measured and analysed for DMABN in neutral solvent n-hexane in the same conditions. We involve also the data of quantum-mechanical calculations, which show that there is a considerable probability of occurrence in solutions of DMABN rotational isomers with differing orientation of the dimethylamino group with respect to the benzonitrile. In the excited state, these have different charge-transfer rates, resulting in a modulation in the intensity ratio of the observed fluorescence bands with change excitation energy quanta on the red wing of the absorption band, doi: 10.1134/S0030400X12050219.     

Fluorescence of the Schiff bases of pyridoxal and pyridoxal 5′-phosphate withl-isoleucine in aqueous solutions

The present study reports on the absorption and emission properties of the Schiff bases formed by pyridoxal and pyridoxal 5-phosphate withl-isoleucine in aqueous solutions. Species protonated at the imine and ring nitrogen are the most fluorescent in both Schiff bases with a quantum yield of 0.02, i.e., 20-fold the value found for species in alkaline solutions. In agreement with other studies, species protonated at the imine nitrogen shows an emission around 500 nm upon excitation at 415 nm. In contrast to previous observations on other PLP Schiff bases, emissions at 560 nm (PL-Ile) and 540 nm (PLP-Ile) are observed upon excitation at 365 and 415 nm, respectively. The emission at 470 nm found in PLP-Ile Schiff base upon excitation at 355 nm is ascribed to a multipolar monoprotonated species. An estimation for the pK _a of the imine in the excited state ( 8.5) for both Schiff bases is also reached. Our results suggest that fast protonation reactions on the excited state are responsible for the observed fluorescence. These effects, in which the hydrogen bond and the phosphate group seem to play a role, could be extended to understanding coenzyme environments in proteins.     

Dispersibility and characterization of polyvinyl alcohol–coated magnetic nanoparticles in poly(glycerol sebacate) for biomedical applications

Journal of Nanoparticle Research - Triggered by experimental observations of nanometer-sized Ni precipitate motion in a La2O3 matrix, the migration and morphological evolution by interface...     

Structural and dielectric properties of polyvinyl alcohol/barium zirconium titanate polymer–ceramic composite

The polyvinyl alcohol (PVA)/barium zirconium titanate Ba[Zr_0.1Ti_0.9]O₃ (BZT) polymer–ceramic composites with different volume percentage are obtained from solution mixing and hot-pressing method. Their structural and electrical properties are characterized by X-ray diffraction (XRD), Rietveld refinement, cluster modeling, scanning electron microscope and dielectric study. XRD patterns of PVA/BZT polymer–ceramics composite (with 50% volume fractions) indicate no obvious differences than the XRD patterns of pure BZT which shows that the crystal structure is still stable in the composite. The scanning electron micrograph indicates that the BZT ceramic is dispersed homogeneously in the polymer matrix without agglomeration. The dielectric permittivity (ε_r) and the dielectric loss (tan δ) of the composites increase with the increase of the volume fraction of BZT ceramic. Theoretical models are employed to rationalize the dielectric behavior of the polymer composites. The dielectric properties of the composites display good stability within a wide range of temperature and frequency. The excellent dielectric properties of these polymer–ceramic composites indicate that the BZT/PVA composites can be a candidate for embedded capacitors.     

Synthesis of hydantoins via N,N′-ureas derived from polymer-bound amino acids

Starting from carboxy-linked amino acids on trityl functionalized polystyrene resin a highly efficient solid-phase synthesis of hydantoins via N, N-ureas was elaborated. The polymer-bound hydantoins can be used as scaffolds for further combinatorial transformations, such as alkylation. Cleavage from the resins yielded the corresponding hydantoins in good yields and purities as shown by ESI-MS and HPLC.     

Influence of the thickness of N,N′-Bis(naphthalene-1-yl)-N,N′-bis(phenyl) benzidine layer on the performance of organic light-emitting diodes

We investigated the influence of the thickness of hole-transport layer, N,N′-biphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB), on the performance of the typical bi-layer organic light-emitting diodes (OLEDs). It was found that both the current efficiency and the power efficiency of bi-layer OLEDs were improved when the thickness of the hole-transport layer varied from 30 to 120 nm. By investigating the hole-injection efficiency of ITO/NPB contact with various thicknesses of NPB film, we found that the hole-injection efficiency was reduced with the thickness of NPB layer increasing from 60 to 180 nm, which improved the injected carriers balance in devices and increased the efficiency of the bi-layer OLEDs.     

Infrared Absorption Study of Some Cyclic Ureas,Cyclic Thioureas and Their N,N′-Dialkyl Derivatives

Abstract

In his communication on the detection limits for thermal emission spectroscopy of metallic species in flame media, Fassel (¹) attacks our previous statement that detection limits for Al, Be and Mo were available only for turbulent oxygen-supported hydrogen or acetylene flames. It should be borne in mind that he was referring to a preliminary communication (²) which naturally does not carry an extensive bibliography. It should also be noted that we were concerned, in context, with a comparison of the separated flame with conventional flames, not with highly unconventional flames such as those to which he refers. Whilst the point with which he takes issue was a very minor one, incorporated in our preliminary communication mainly as an “aside”, we firmly disagree with his observation. The flame he refers to (³) (⁴) is, in fact, a diluted oxy-acetylene flame which is supported by venting some air (and therefore nitrogen) to dilute the fuel-oxygen mixture. Fassel's communication (¹) erroneously refers to this as a 'premixed oxy-acetylene flame', whereas elsewhere (⁵) it is described more correctly as an oxygen-nitrogen-acetylene flame. The burner he long-pathlength carbonaceous flames (¹⁰). They also allow more sensitive molecular emission spectroscopy of sulphur in an air-hydrogen flame (¹¹), etc. We hope that this unfortunate correspondence will not distract attention from the main issue of our previous or previous preliminary communication on the separated nitrous oxide-acetylene flime.     

Structural,thermal and electrical properties of polyvinyl alcohol/poly(vinyl pyrrolidone)–sodium nitrate solid polymer blend electrolyte

Sodium ion conducting solid polymer blend electrolyte thin films have been prepared by using polyvinyl alcohol (PVA)/poly(vinyl pyrrolidone) (PVP) with NaNO₃ by solution cast technique. The prepared films were characterized by various methods. The complexation of the salt with the polymer blend was identified by X-ray diffraction (XRD) and Fourier transforms infrared spectroscopy (FTIR), Differential scanning calorimetry was used to analyze the thermal behavior of the samples, and the glass transition temperature is low for the highest conducting polymer material. The scanning electron microscopy gives the surface morphology of the polymer electrolytes. The frequency and temperature dependent of electrical conductivities of the films were studied using impedance analyzer in the frequency range of 1 Hz to 1 MHz. The highest electrical conductivity of 50PVA/50PVP/2 wt% NaNO₃ concentration has been found to be 1.25 × 10^?5 S cm^?1 at room temperature. The electrical permittivity of the polymer films have been studied for various temperatures. The transference number measurements showed that the charge transport is mainly due to ions than electrons. Using this highest conducting polymer electrolyte, an electrochemical cell is fabricated and the parameters of the cells are tabulated.     

Spectroscopic Study on the Photophysical Properties of Lanthanide Complexes with 2, 2′-Bipyridine-N, N′-dioxide

Five novel lanthanide (Eu3+, Tb3+, Gd3+, Sm3+ and Dy3+) complexes with 2, 2'-bipyridine-N, N'-dioxide (bipyO2) were synthesized and characterized by elemental analysis, IR spectrum. The triplet state energy of bipy O2 was determined to be 22275 cm(-1) with the phosphorescence spectrum of bipy O2 and its gadolinium complex. The photophysical properties of these complexes indicated that the triplet state energy of the ligand is suitable for the sensitization of the luminescence of Eu3+, Tb3+, Sm3+ and Dy3+, especially of Tb3+.     

Positive domain wall resistance of 180 degrees Néel walls in Co thin films

We measured the intrinsic domain wall resistance (DWR) of 180 degrees Ne el walls in a polycrystalline Co thin film deposited on top of a patterned antiferromagnetic CoO template. After field cooling through the CoO blocking temperature, exchange bias induces a spatially modulated coercivity of the Co film, resulting in a periodic domain pattern with 180 degrees Ne el walls. The intrinsic DWR is determined unambiguously by using rotating magnetic fields that result in a reversible creation and annihilation of the Ne el walls. In contrast with earlier reports, the DWR is positive and in agreement with models based on the giant magnetoresistance mechanism. A reliable, quantitative determination of the DWR requires careful numerical evaluation of the anisotropic magnetoresistance effect.     

Ambiguities on structure analysis of Fe–N thin films

Fe–N thin films with good soft magnetic properties were prepared by RF sputtering and vacuum annealed at 250°C under 12000 A/m magnetic field for 4 h. The structure of α′ in thin films deposited at room temperature is different from α′ formed through the Bain mechanism in bulk samples. In thin films, the lattice parameters of α′ are $\text{c=2.866+1.559}\text{C}{}_{\mathrm{<mtext>N</mtext>}}{}^{\mathrm{<mtext>\alpha </mtext><mtext>\prime </mtext>}}\text{,a=2.864+0.181}\text{C}{}_{\mathrm{<mtext>N</mtext>}}{}^{\mathrm{<mtext>\alpha </mtext><mtext>\prime </mtext>}}$.     

Thermal Behavior of the Fluorescence Lines of Ho~(3 ) in Cr,Tm,Ho∶YAG

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｃｒ,Ｔｍ ,Ｈｏ∶ＹＡＧｉｓａｋｉｎｄｏｆｖｅｒｙｉｍｐｏｒｔａｎｔ 2 μｍｌａｓｅｒｃｒｙｓｔａｌ,ｗｈｏｓｅ 2 .1 μｍｌａｓｅｒｉｓａｂｓｏｒｂｅｄｓｔｒｏｎｇｌｙｂｙｗａｔｅｒｃｏｍｐｏｎｅｎｔｏｆｔｉｓｓｕｅ,ｒｅｓｕｌｔｉｎｇｉｎｓｈａｌｌｏｗｔｉｓｓｕｅｐｅｎｅｔｒａｔｉｏｎａｎｄｇｏｏｄｓｕｒｇｉｃａｌｐｒｅｃｉｓｉｏｎｉｎｍｏｓｔｔｙｐｅｓｏｆｓｏｆｔａｎｄｈａｒｄｔｉｓｓｕｅ .Ｈｏ∶ＹＡＧｌａｓｅｒｈａｓｂｅｃｏｍｅａｎｉｍｐｏｒｔａｎｔｓｏｕｒｃｅ…     

Absorption and luminescence spectroscopic analysis of tautomeric forms of protonatedN,N-dimethyl-N′-(1-nitro-9-acridinyl)-1,3-propanediamine (nitracrine) and its nitro isomers in poly(vinyl alcohol) films

The electronic absorption, fluorescence, and phosphorescence excitation spectra, as well as the fluorescence and phosphorescence spectra, at either room or liquid nitrogen temperatures, were measured forN,N-dimethyl-N-(1-nitro-9-acridinyl)-1,3-propanediamine and its three nitro isomers in acidified poly(vinyl alcohol) (PVA) film. The spectral characteristics obtained reveal the existence of the compounds studied in at least two structural forms. The results are interpreted in terms of the tautomeric phenomena which originate due to the migration of the hydrogen atom, which is bound to the nitrogen atom attached to the carbon atom (9), to the acridine ring nitrogen.