Stereospecific Synthesis and Photophysical Properties of Propeller-Shaped C90H48 PAH

Herein, we have synthesized an enantiomerically pure propeller-shaped PAH, C₉₀H₄₈, possessing three [7]helicene and three [5]helicene subunits. This compound can be obtained in gram quantities in a straightforward manner. The photophysical and chiroptical properties were investigated using UV/Vis absorption and emission, optical rotation and circular dichroism spectroscopy, supported by DFT calculations. The nonlinear optical properties were investigated by two-photon absorption measurements using linearly and circularly polarized light. The extremely twisted structure and packing of the homochiral compound were investigated by single-crystal X-ray diffraction analysis.     

Comparing results of X-ray diffraction, µ-Raman spectroscopy and neutron diffraction when identifying chemical phases in seized nuclear material,during a comparative nuclear forensics exercise

Journal of Radioanalytical and Nuclear Chemistry - This work presents the results for identification of chemical phases obtained by several laboratories as a part of an international nuclear...     

Energetic distribution of the electrons from a 200 keV beam in polyurethane layers : EGS4 calculation and FTIR analysis

The aim of this study is to characterize the chemical transformation of a polymer resulting from irradiation by a 200 keV electron beam. Thermoplastic PU polyetherurethane material was used and irradiation was performed with applied electron fluences in the range of 10¹⁴–10¹⁷ electron cm⁻² at 77 K.

The chemical changes have been observed by FTIR analysis of irradiated layers. A NH bond evolution study has allowed us to follow polymer degradation versus depth and fluence. The results have been compared to a simulation of electronic energy loss and to the energy spectrum of the generated electrons in the polymer using EGS4 code.     

A review on use of TRNSYS as simulation tool in performance prediction of desiccant cooling cycle

Journal of Thermal Analysis and Calorimetry - Solid desiccant-assisted cooling and dehumidification systems are becoming very popular nowadays for maintaining the required thermal comfort in...     

Breaking the Semi‐Quinoid Structure: Spin‐Switching from Strongly Coupled Singlet to Polarized Triplet State

2,7‐TMPNO (4,5,9,10‐tetramethoxypyrene‐2,7‐bis(tert‐butylnitroxide)) was found to exist in semi‐quinoid form with unprecedented strong intramolecular magnetic exchange interaction of 2 J/k_B=1185 K operating over a distance of 10 Å. Structural transformations with the activation energy of ΔE_eq=949 K were observed by varying the temperature, from more quinoid structure at low temperature to more biradicaloid structure at higher temperature. Moreover, this molecule undergoes a transient spin transition from singlet to polarized triplet state upon photoexcitation revealed by TREPR spectroscopy. The spin Hamiltonian parameters were determined to be S=1, g=2.0065, D=?0.0112 cm^?1, and E=?0.0014 cm^?1 by spectral simulation with the hybrid Eigenfield/exact diagonalization method.     

Electron irradiation of polyesterurethane: study of chemical and structural modifications using FTIR, UV spectroscopy and GPC

To understand the electron irradiation effects on polymers, a polyesterurethane (ESPU) was irradiated by a 200 keV electron beam perpendicular to the surface under a vacuum of 0.04 Torr with electron fluxes of 0.25–1.25×10¹³ s⁻¹ on the irradiated zone. To perform a study of ESPU degradation versus the electron's penetration depth, a stratified structure was made with seventeen 30-μm-thick films. The irradiation was performed at both room temperature (293 K) and 77 K. The applied fluence was in the range of 10¹⁴–10¹⁷ cm⁻². Chemical transformations, such as degradation and oxidation, are studied by FTIR, by following NH and OH bond evolution, and by UV spectroscopy, by following the absorbance shift towards the visible region. These effects are analyzed versus depth, fluence and electron flux. Structural transformations are also characterized by GPC for soluble samples. An increase of crosslinking rate of the polymer is observed and analyzed.     

Effect of synthesis temperature and doping level on conductivity and structure of poly(3-methyl thiophene)

Poly(3-methyl thiophene) was synthesized by oxidative chemical polymerization technique using ferric chloride as the dopant in an inert atmosphere. Samples of different doping levels were prepared and analyzed by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, and direct current (DC) conductivity measurement at room temperature (300 K). Synthesis of the polymer was confirmed by FTIR studies. FTIR spectra showed a shift in the heterocyclic bands in the region of 700-1200 cm(-1) with a decrease in synthesis temperature. It was evident from the scanning electron micrographs that the surface structure of the polymer became denser with an increase in doping level. The measured DC conductivity increased initially up to the doping level of 0.8 M and then this increase tended to slow down. Samples having a doping level of 0.4 M were synthesized at 300, 280, and 270 K while maintaining the other synthesis parameters. The conductivity and yield were found to increase as the temperature of the polymerization decreased.     

Synthesis of Nitrogen‐Doped ZigZag‐Edge Peripheries: Dibenzo‐9a‐azaphenalene as Repeating Unit

A bottom‐up approach toward stable and monodisperse segments of graphenes with a nitrogen‐doped zigzag edge is introduced. Exemplified by the so far unprecedented dibenzo‐9a‐azaphenalene (DBAPhen) as the core unit, a versatile synthetic concept is introduced that leads to nitrogen‐doped zigzag nanographenes and graphene nanoribbons.