COMFORMATIONAL ANALYSIS AND ELECTRONIC PROPERTIES OF FLUOROMETHYLFURAN OLIGOMERS: SEMIEMPIRICAL AND DFT STUDY

Structural and electronic properties of oligomers of fluoromethylfurans (FMFs), OC4H4-CHnF3-n with n = 1, 2, 3 and 4 have been studied using ZINDO/AM1 and B3LYP/6-31G(d) basis set. Preliminary study using AM1 and ab initio (HF) 6-31G(d) with medium basis set was carried out on di-, tri- and tetramer FMFs in order to investigate the stability of configuration of the polymer chains and conformation analysis of the dimers. There is noticeable effect of substituents on the geometries of FMFs as compared to polyfuran, polymethylfuran and chloromethylfuran (CMF) analogues [11]as well as improved characteristics as conducting polymers compared polymethylfurans and CMFs. The most stable conformation is the anti-planar conformation except in fluoromethylfuran in which antigauche conformation is most stable. The energy band gaps, electronic spectroscopy and electronic dipole moment vectors of the compounds are presented. Generally FMFs present lower energy band gaps, longer wavelength and higher electric dipole moments and are therefore more suitable as monomer for conducting polymer especially trifluoromethylfuran.

EFFECT OF SYNTHESIS REACTION TIME AND DOPING ON UV/VIS ABSORPTION OF POLYENE COATING

Absorbance spectra and energy band gap of synthesizing polyene from dechlorination of polyvinyl chloride (PVC) with varying synthesizing reaction times and doping percentages were examined in this paper. The reaction time of dechlorination was varied from 30 minutes, 1 hour, 2 hours and 4 hours. Polyene obtained from the dechlorination reaction was doped with potassium iodide (KI). Sample for UV/Vis test was prepared in the form of film. Modified EO film as control sample showed that there is only a single absorption peak around 327nm. The C-Cl adsorption band link from source link polymer was observed at 422nm and all polyene film samples and new bands absorption were observed from 422nm to 590nm, and 683nm upon the increase in reaction time. The lower energy band gap was observed at 683.18nm absorption with 1.08eV.

Thickness Dependent on Energy Band Gap and Electrical Conductivity of Undoped Conjugated Polymer Thin Films

Conjugated polymers have been widely used for electronic purpose applications due to their numerous advantages. This has led many researches to pay their major attention in studying on characteristics of conjugated polymer thin films. The purpose of this study was to investigate the effect of undoped conjugated polymer thin films on their optical and electrical properties. Poly(3-thiophene acetic acid), Polypyrrole and Polythiophene thin film was fabricated on ITO glass substrate by using EIS. Film thickness, energy band gap and electrical conductivity of thin films were characterized by using profilometer, ultraviolet-visible spectrometer and four point probe method respectively. The thickness of each thin film varied between 50.534 nm to 97.03 nm. The result has shown that thicker film has lower energy band gap compared to the thinner one. However the electrical conductivity showed an opposite behavior.

Growth evolution and phase transition from chalcocite to digenite in nanocrystalline copper sulfide: Morphological, optical and electrical properties

Copper sulfide is a promising p-type inorganic semiconductor for optoelectronic devices such as solar cells, due its small band gap energy and its electrical properties. In this work nanocrystalline copper sulfide (Cu x S), with two stoichiometric ratios (x = 2, 1.8) was obtained by one-pot synthesis at 220, 230, 240 and 260 °C in an organic solvent and amorphous Cu x S was obtained in aqueous solution. Nanoparticle-like nucleation centers are formed at lower temperatures (220 °C), mixtures of morphologies (nanorods, nanodisks and nanoprisms) are seen at 230 and 240 °C, in which the nanodisks are predominant, while big hexagonal/prismatic crystals are obtained at 260 °C according to TEM results. A mixture of chalcocite and digenite phases was found at 230 and 240 °C, while a clear transition to a pure digenite phase was seen at 260 °C. The evolution of morphology and transition of phases is consistent to the electrical, optical, and morphological properties of the copper sulfide. In fact, digenite Cu1.8S is less resistive (346 Ω/sq) and has a lower energy band gap (1.6 eV) than chalcocite Cu2S (5.72 × 105 Ω/sq, 1.87 eV). Low resistivity was also obtained in Cu x S synthesized in aqueous solution, despite its amorphous structure. All Cu x S products could be promising for optoelectronic applications.

NONLINEAR OPTICAL PROPERTIES OF mSTRAWBERRY AND mCHERRY FOR SECOND HARMONIC IMAGING

The second-order nonlinear optical properties of two monomeric red fluorescent proteins, mStrawberry and mCherry, have been experimentally determined by frequency-resolved femtosecond hyper-Rayleigh scattering. These proteins were found to exhibit a stronger nonlinear response than the previously described eGFP, eYFP and DsRed,1 confirming the trend that fluorophores with a more extended conjugated system, or a lower-energy band gap between ground and excited state, exhibit a larger static hyperpolarizability (β0). Furthermore, these experimental data were complemented with quantum chemical calculations. A discrepancy was observed between experimental and theoretical results, but this could be explained by the chromophore model extracted from the available X-ray diffraction data. While eGFP showed a larger dynamic experimental response (βHRS) due to the highest resonance enhancement, we measured an even higher signal for mCherry. Furthermore, mCherry also shows a better separation of the second harmonic signal and two-photon excited fluorescent signal, making this the preferred fluorescent protein for second harmonic imaging at 800 nm so far.

Theoretical Study on the Influence of Iron Mordant in the Optical Properties of Natural Dyes

Geometry optimization of free alizarin, purpurin and luteolin and coordinated Fe(II) complexes was performed at DFT/B3LYP level. TD-DFT spectra were also calculated for free and coordinated alizarin and luteolin. For the Fe(II) complexes several spin multiplicities have been calculated and quintuplet spin structures were found to be the most stable. In the luteolin-Fe(II) complex, the coordination of the chromophore with the iron leads to a decrease in the lower energy band. In the case of luteolin complex, a new band emerges due to interactions between the delocalized π electrons of the luteolin molecule with the d metal orbitals.

Flares and MHD Jets in Protostar

By using ASCA, Koyama et al. (1994, 1996) carried out a systematic survey of hard X-ray sources in molecular clouds and revealed that protostars are strong hard X-ray emitting sources. Some of them show flare-like activities. Protostellar flares differ from solar flares in their total energy(1035-36 erg), size(several times the radius of protostar), and higher temperature(8keV). Protostellar flares are also observed in lower energy band by ROSAT in YLW15 (Grosso et al. 1997). By extending the model of solar flares associated with footpoint shearing motion, we proposed a model of protostellar flares in which the magnetic field connecting the protostar and the disk disrupt by twist injection from the rotating disk(Hayashi et al. 1996).

Optical Properties of Ingan/GaN Multi Quantum Well Structures

A set of GaN/InGaN multiple quantum wells (QWs) with well thickness 30 Å and barrier thickness 60 Å were grown by MOCVD on sapphire substrates. The n-type Si doping of the InGaN QWs was varied, in order to produce a different electron concentration in the QWs for the different samples. Optical spectra were obtained by time resolved photoluminescence spectroscopy. The data show weak excitonic spectra from the QWs as well as a broad deeper emission with a much stronger intensity. The spectral shape becomes narrower and the energy position shifts to higher energies with increasing doping. The two different emissions are not easily separated in CW or time integrated spectra, but are clearly observed in a time resolved spectral measurement due to their different recombination rates. The deeper emission has a long and non-exponential decay, with an average decay time in the order of several hundred nanoseconds. The higher energy exciton emission has a much faster decay of about 1 ns. The lower energy band is tentatively explained as due to separately localized electron-hole (e-h) pairs in the QW.

Energy Localisation and Surface Interactions in the Luminescence of Porous Silicon

The fundamental mechanisms controlling the light emission from porous Si remain unresolved. In this paper we report attempts to modify the luminescence using a variety of surface processing steps, such as vacuum annealing with subsequent anneals in nitrogen and oxygen, exposure to hydrofluoric acid (HF) and rapid thermal oxidation. Luminescence, infrared absorption, and electron spin resonance (ESR) have all been used to gain more information on the link between the optical emission and the localisation of the electrons in this material system. We present evidence that the silicon dangling bond is the key component in the non-radiative recombination. This is based on measurements shown that hydrogen coverage of the surface is significant because of saturation of the dangling bonds and a subsequent reduction in the competing non-radiative paths rather than as an active component in the radiative transition. Finally, we focus our attention upon the lower energy band which appears in the luminescence spectrum of porous Si (∼0.9eV) by examining its behavior under the surface treatments mentioned above. We found that this luminescence band originates from the surface of the porous layer and its intensity correlates well with increasing oxidation of the porous layer.

A Photoluminescence Study of Cd Related Centers in InP

We report the results of a low temperature photoluminescence study of Cd related centers in InP. Besides the previously identified 1.365 eV band a new Cd related band is reported. The peak position of this band lies in the energy ranqe 1.2-1.3 eV at 5.5K dependinq upon the excitation intensity. The peak position of the bands shifts to higher energy with increasing excitation intensity but the change in the peak energy per decade chanqe in excitation intensity is much larger (50 meV) for the lower energy band compared to the 1-2 meV shift for the 1.365 eV band. Both bands exhibit thermal quenching of luminescence above lOOK with an activation energy of 54±4 meV which is comparable to the ionization energy for the substitutional Cd acceptor, CdIn. From this we infer that both bands involve the CdIn acceptor in the recombination process. While the excitation dependence of the bands suggests a donor-to-acceptor pair recombinaton for their origin, we present arguments to show that the larger shift of the peak energy of the 1.2-1.3 eV band with excitation intensity is perhaps a consequence of the involvement of a deep donor in its origin as opposed to a shallow donor in the 1.365 eV band. It is suggested that the deep donor is related to Cd and possible centers are discussed.