Investigation of a Photochromic Diarylethene with Electron-acceptor Attached

In this contribution, an electron acceptor attached diarylethene derivative was synthesized and fully characterized. The photochromic behavior was investigated in THF. Under exposure of UV and visible light cycles, the solution color can be switched between colorless and yellow smoothly. Fatigue resistance measurements could be repeated 50 times with an acceptable degradation. Due to the electron acceptor attached to the framework of diarylethene, the photo- and thermal-stability were enhanced both. A full-photo mode switch can be established based on the well-defined states by external excitation. The molecular structures of ring-open and ring-closed form were optimized by Dmol³. The distance between photocyclizing atoms in aptiparallel conformation meets the requirement for photochromic reaction. And the calculated absorption wavelengths were also in agreement with the experimental values.     

Synthesis of the Copolymer Based on Diketopyrrolopyrrole with Didecyl Chain for OPVs

A new accepter unit, diphenylpyrrolo[3,2-b]pyrrole-2,5-dione with didecyl chain, was prepared and utilized for the synthesis of the conjugated polymer containing electron donor-acceptor pair for OPVs. The iDPP, part of the structure of a natural dye found in lichens, is the regioisomer of the known DPP with switched position of the carbonyl group and nitrogen atom. At the 4-positions of the N-substituted phenyl groups of 1,4-bis(4-butylphenyl)-pyrrolo[3,2-b]-pyrrole-2,5-dione unit in P-butyl, the butyl group was substituted with decyl group to increase solubility. The absorption spectrum of polymer with diphenylpyrrolo[3,2-b]pyrrole-2,5-dione unit exhibit two maximum peaks at about 365 and 542 nm. The spectrum of the P1 as the solid thin film shows absorption band with maximum peaks at 370 and 536 nm, and the absorption onset at 703 nm, corresponding to band gap of 1.76 eV. The oxidation and reduction potential onset of the synthesized polymer were estimated to be 0.84 and ?1.22 V, which correspond to HOMO and LUMO energy levels of ?5.64 and ?3.58 eV, respectively. The devices comprising P1 with PC₆₁BM annealed at 100°C showed a V_OC of 0.79 V, a J_SC of 1.75 mA/cm², and a FF of 0.31, leading to the power conversion efficiency of 0.43% under white light illumination (AM 1.5 G, 100 mW/cm²).     

Theoretical Design Study on the Electronic Structures and Phosphorescent Properties of Four Iridium(III) Complexes

The geometry structures, electronic structures, absorption, and phosphorescent properties of four Ir(III) complexes have been investigated using the density functional method. Calculations of ionization potential (IP) and electron affinity (EA) were used to evaluate the injection abilities of holes and electrons into these complexes. The result also indicates that the –CF₃ substituent group on the ligand not only change the character of transition but affect the rate and balance of charge transfer. The lowest energy absorption wavelengths are located at 428 nm for 1a, 446 nm for 1b, 385 nm for 2a, and 399 nm for 2b, respectively, in good agreement with the energy gap (ΔE_L-H) trend because the HOMO–LUMO transition configurations are predominantly responsible for the S₀→S₁ transition. 2b has the 433 nm blue emission, which might be a potential candidate for blue emitters in phosphorescent dopant emitters in organic light emitting diodes (OLEDs). The study could provide constructive information for designing novel OLEDs materials in the future.

[Supplemental materials are available for this article. Go to the publisher's online edition of Molecular Crystals and Liquid Crystals to view the free supplemental file.]     

Photochromic behavior of Li-stabilized MoO3 sol–gels

Photochromic behavior of Li-doped MoO₃ sol–gels prepared by the peroxo sol–gel method was studied in details using various experimental techniques, including UV–vis, XRD, Raman, EPR, and XPS. The lithium doping has drastically enhanced the stability of the MoO₃ sol–gels. Upon UV-light irradiation from a high-pressure mercury lamp, the Li-doped MoO₃ sol turned from yellowish into deep blue, and the sol in ethanol exhibited much more intense color change than the sol in water. The UV-light exposure has the effect of re-arranging the structural units of MoO₃ and building up short-range order inside the solid. The formation of a blue colored bronze in the photo-irradiated sols because of the reduction of Mo⁶⁺ to Mo⁵⁺ is also evidenced by the experimental data. Based on these data, a mechanism for the photochromic behavior is proposed.     

Study of the surface state density and potential in MIS diode Schottky using the surface photovoltage method

ABSTRACT

The effects of surface preparation and illumination on electric parameters of Au/GaN/GaAs Schottky diode were investigated. The thin GaN film is realized by nitridation of GaAs substrates with different thicknesses of GaN layers (0.7 – 2.2 nm). In order to study the electrical characteristics under illumination, we use an He-Ne laser of 632 nm wavelength. The I(V) current- voltage, the surface photovltage SPV measurement were plotted and analysed taking into consideration the influence of charge exchange between a continuum of the surface states and the semiconductor. The barrier height Ф_Bn, the serial resistance R_s and the ideality factor n are respectively equal to 0.66 eV, 1980 Ω, 2.75 under dark and to 0.65 eV, 1160 Ω, 2.74 under illumination for simple 1 (GaN theckness of 0.7 nm). The interface states density N_ss in the gap and the excess of concentration δn are determined by fitting the experimental curves of the surface photovltage SPV with the theoretical ones and are equal to 4.5×10¹² eV^?1 cm^?2, 5×10⁷ cm^?3, respectively, for sample 1 and 3.5×10¹² eV^?1 cm^?2, 7×10⁸ cm^?3 for sample 2 (GaN theckness of 2 nm). The results confirm that the surface photovoltage is an efficient method for optical and electrical characterizations.     

Effect of high-energy electron irradiation in an electron microscope column on fluorides of alkaline earth elements (CaF2, SrF2, and BaF2)

The effect of high-energy (150 eV) electron irradiation in an electron microscope column on crystals of fluorides of alkaline earth elements CaF₂, SrF₂, and BaF₂ is studied. During structural investigations by electron diffraction and electron microscopy, the electron irradiation causes chemical changes in MF₂ crystals such as the desorption of fluorine and the accumulation of oxygen in the irradiated area with the formation of oxide MO. The fluorine desorption rate increases significantly when the electron-beam density exceeds the threshold value of ∼2 × 10³ pA/cm²). In BaF₂ samples, the transformation of BaO into Ba(OH)₂ was observed when irradiation stopped. The renewal of irradiation is accompanied by the inverse transformation of Ba(OH)₂ into BaO. In the initial stage of irradiation of all MF₂ compounds, the oxide phase is in the single-crystal state with a lattice highly matched with the MF₂ matrix. When the irradiation dose is increased, the oxide phase passes to the polycrystalline phase. Gaseous products of MF₂ destruction (in the form of bubbles several nanometers in diameter) form a rectangular array with a period of ∼20 nm in the sample.     

Synthesis and Characterization of Violet Light Emitting Polymer based on Fluorene and Dimethylsilane

New fluorene based light emitting polymer, poly[(4-(9,9-didecyl-9H-fluoren-2-yl) phenyl)dimethyl(phenyl)silane] (PFDPS), was synthesized by palladium-catalzed Suzuki coupling reaction. The obtained copolymer was characterized by ¹H-NMR, and IR-spectroscopy. The polymer showed good solubility in common organic solvents and weight average molecular weight of 16,300 with polydispersity index of 1.4. The maximum photoluminescence of the solution and film of the polymer was observed at 392 nm and 410 nm, respectively.

The double-layered device with the configuration, ITO/PEDOT/PFDPS/LiF/Al structure has a turn-on voltage at about 5.5 V and maximum brightness of 9.40 cd/m², and emitted violet light at 414 nm.     

Synthesis of a BDT-based small-molecule acceptor with dye end groups for organic photovoltaic cell application

ABSTRACT

An acceptor-donor-acceptor (A–D–A)-type small molecule, BDT-IN, having a benzo[1,2-b:4,5-b']dithiophene (BDT) unit as its electron-donating core (D) and an 1,3-indanedione (IN) unit as its electron-withdrawing end group (A), was synthesized by Knoevenagel condensation. The BDT-IN film showed broader UV absorption with a greater red shift (λ_max = 622 nm) than that of the BDT-IN solution (λ_max = 570 nm). The organic photovoltaic cells were fabricated with an ITO/PEDOT:PSS/poly(3-hexylthiophene): BDT-IN/LiF/Al configuration, and showed a power conversion efficiency of 0.23%.     

Dependence of photochromic damage on polarization in KTiOPO4 crystals

Studies of photochromic damage induced in KTiOPO₄ single crystals by 514.5 nm laser irradiation is reported. A dependence of photochromic damage on polarization was observed. Along the same propagation direction (θ=90°, ϕ=23.3°), the gray-track susceptibility for ∥z polarization irradiation is one order magnitude lower than that for ⊥z polarization irradiation for KTP crystal. The results clearly show that in KTiOPO₄, a correlation exists between the gray-track susceptibility and the ionic electrical conductivity. Due to a high ionic electrical conductivity along the polar z-axis, the optical absorption centers will be annihilated with ∥z polarization irradiation as soon as they are produced. This results in a lower gray-track susceptibility for ∥z polarization irradiation.     

A BODIPY-based highly emissive dye with thiophene-based branch harvesting the light

ABSTRACT

A novel BODIPY-based dye with highly emissive character was configured by Sonogashira coupling and routinely characterized by NMR and MS technology. The emission of dye was investigated in solution/film/solid and shows intensive emission. In solution, the emission peak appeared around 510 nm with little influence by the polar environment. The terthiophene plays an effective antenna effect, harvesting the light and transferring the energy to BODIPY. The pseudo Stoke's shift enlarged to ～170 nm in solution. In film, the emission peak shifted to 563 nm in polycarbonate matrix. And it shifted further to 585 nm in solid due to the highly twisted structure, which avoided closely regular-tight packing. The dye rendered an intense fluorescence, good optothermal stability, and high fluorescence quantum yield (0.55). The solid emission showed highly red emission with Commission Internationale de L'Eclairage (CIE) coordinates of (X = 0.69, Y = 0.31). Thus, the synthesized dye is idea candidate for emitting materials.     

Synthesis and electroluminescent properties of new diazocine derivatives

ABSTRACT

DAPCz and DANaPCz have been successfully synthesized and characterized. DAPCz and DANaPCz in film state showed absorption in the range of 322 to 345 nm wavelength and exhibited blue photoluminescence (PL) emission peaks at 428 and 425 nm. PL wavelength of DAPCz is red-shifted by 3 nm than that of DANaPCz, which is due to the carbazole electron donating group of DAPCz. The use of DAPCz in a non-doped OLED device resulted in blue emission with current efficiency of 1.01 cd/A and C.I.E. of (0.26, 0.37).     

Microwave-assisted green synthesis of SnO2 nanoparticles and their optical and photocatalytic properties

Abstract

In this study, SnO₂ has been synthesized using Andrographis Paniculata (A. Paniculata) by microwave-assisted method. It is also characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). It exhibits the tetragonal structure with average crystallite size of 27?nm. The stretching vibration peak of Sn-O-Sn is 670?cm^?1. SEM reveals the formation of nanoparticles. The bandgap was estimated by the tauc’s relation as 3.52?eV from the UV-Visible (UV-Vis) spectra. Biosynthesized SnO₂ nanoparticles show excellent photocatalytic activity against Congo red dye under sunlight irradiation.     

Synthesis and Nonlinear Optical Properties of Novel Polyester Containing Nitrophenylazonitroresorcinoxy Group

A new X-type polyester (4) containing nitrophenylazonitroresorcinoxy groups as NLO chromophores, which are components of the polymer backbone was prepared. Polyester 4 is soluble in common organic solvents such as N,N-dimethylformamide and dimethylsulfoxide. It shows a thermal stability up to 280°C from thermogravimetric analysis with glass-transition temperature (T_g) obtained from differential scanning calorimetry near 120°C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer films at the 1064 nm fundamental wavelength is around 5.08 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 5°C higher than T_g, and no SHG decay was observed below 125°C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.     

Synthesis and Nonlinear Optical Properties of Novel Polyurethane Containing Cyanovinylnitroresorcinoxy Group

Novel X-type polyurethane 5 containing 4-(2′-carbomethoxy-2′-cyano)vinyl-6-nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute part of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It shows thermal stabilities up to 260°C from thermogravimetric analysis with glass transition temperature obtained from differential scanning calorimetry near 108°C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at 1064 nm fundamental wavelength is 9.83 × 10^?9 esu. Polymer 5 exhibits a high thermal stability even at 2°C higher than T_g, and no significant SHG decay is observed below 110°C, which is acceptable for nonlinear optical device applications.     

Synthesis and Properties of Novel Nonlinear Optical Polyester Containing Cyanovinylnitroresorcinoxy Group

Novel X-type polyester 5 containing 4-(2’-carbomethoxy-2’-cyano)vinyl-6-nitroresorcinoxy group as nonlinear optical (NLO) chromophore, which constitutes parts of the polymer backbone, was prepared and characterized. Polyester 5 is soluble in common organic solvents such as N,N-dimethylformamide and acetone. Polyester 5 shows a thermal stability up to 280°C from thermogravimetric analysis with glass-transition temperature obtained from differential scanning calorimetry of near 116°C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at the 1064 nm fundamental wavelength is 4.25 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 4°C higher than glass-transition temperature (T_g), and no significant SHG decay is observed below 120°C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.     

New Mesogenic Compounds Containing a Terminal-Substituted Benzoxazole Unit

A series of novel mesogenic 2-(4-alkoxyphenyl-1-yl)-benzoxazole derivatives bearing different substituents (H, NO₂, CH₃, Cl, coded as nPB-H, nPB-N, nPB-M, and nPB-C, respectively) at the 5-position were prepared and characterized. nPB-N, nPB-M, and nPB-C exhibited enantiotropic smectic mesophases with the mesophase ranges 3 °C–32 °C and 3 °C–82 °C on heating and cooling processes, whereas nPB-H showed no mesophases. The substituents with the stronger electron withdrawing effect let to the wider mesomorphic temperature domain. The nPB-M, nPB-C, and nPB-H displayed intense emission in CH₂Cl₂ solutions with λ_max peaks of the photoluminescence spectra at 350–355 nm when excited at their absorption maxima.     

Structural analysis of 1,1′-bis(diphenylphosphino)ferrocene dioxide

The title compound 1,1′-bis(diphenylphosphino)ferrocene dioxide has been analyzed by X-ray crystal diffraction analysis. The crystals are monoclinic, space group P2(1)/c with a = 22.461(5), b = 10.515(2), c = 12.024(2) Å, α = 90, β = 96.28(3), γ = 90°, V = 2822.7(10) ų, Z = 4, F(000) = 1256, D_c = 1.422 g/cm³, μ = 0.683 mm^?1, the final R = 0.0514 and wR = 0.1369. A total of 22218 reflections were collected, of which 4957 were independent (R_int = 0.0422). In the crystal packing diagram, intermolecular O?H···O hydrogen bonds between the P=O and H₂O stabilize the solid state of the title compound.     

Emission behavior of naphthalimide-coumarin cassette

ABSTRACT

In this contribution, a dye (C₈-alkyl substituted Naphthalimide-Coumarin, CNC) with naphthalimide and coumarin incorporated together with -NHN = bridge unit. The compound was fully characterized by NMR and HRMS spectroscopic techniques. Highly emissive character was investigated in detail in various polar environments. The emission maximum varied from 430 to 470 nm. In polycarbonate film, CNC is also highly emissive with 560 nm emission peak. While in sold, the emission maximum was further shifted to 580 nm due to the more tightly packing mode than that in film. The C₈-alkyl substitution enhances the solubility of CNC and also contributes most to its solid emission.     

Enhancement of the emission from TeO2 nanorods by encapsulation with ZnO

TeO₂‐core/ZnO‐shell nanorods were synthesized by a two–step process comprising thermal evaporation of Te powders and atomic layer deposition of ZnO. Scanning electron microscopy images exhibit that the core‐shell nanorods are 50 ‐ 150 nm in diameter and up to a few tens of micrometers in length, respectively. Transmission electron microscopy and X‐ray diffraction analysis revealed that the cores and shells of the core‐shell nanorods were polycrystalline simple tetragonal TeO₂ and amorphous ZnO with ZnO nanocrystallites locally, respectively. Photoluminescence measurement revealed that the TeO₂ nanorods had a weak broad violet band at approximately 430 nm. The emission band was shifted to a yellowish green region (∼540 nm) by encapsulation of the nanorods with a ZnO thin film and the yellowish green emission from the TeO₂‐core/ZnO‐shell nanorods was enhanced significantly in intensity by increasing the shell layer thickness. The highest emission was obtained for 125 ALD cycles (ZnO coating layer thickness: ∼15 nm) and its intensity was much higher than that of the emission from the uncapsulated TeO₂ nanorods. The origin of the enhancement of the emission by the encapsulation is discussed in detail. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Small-angle neutron scattering study of radiation-induced defects in synthetic quartz

The supraatomic structure of single crystals of synthetic quartz was studied by thermal neutron small-angle scattering in the initial state (dislocation densities 54 and 570 cm⁻²) and after irradiation in the WWR-M reactor (Petersburg Nuclear Physics Institute) by fast neutrons with energies E _n > 0.1 MeV at fluences F _n = 0.2 × 10¹⁷ −5 × 10¹⁸ neutrons/cm². It is established that fast neutrons form point, linear, and volume defects in the lattice throughout the entire volume of a sample. Large-volume structures—amorphous-phase nuclei—reach sizes of ∼100 nm in quartz, while occupying a small total volume of ∼0.3% even at the maximum fluence 5 × 10¹⁸ neutrons/cm². The main fraction of the damaged volume (up to 5%) corresponds to point (with a radius of gyration of 1–2 nm) and linear defects, giving a comparable contribution (∼1–4%). The extended linear structures with a radius of 2 nm, even at a moderate fluence of 7.7 × 10¹⁷ neutrons/cm², have a significant total length per volume unit (∼10¹¹ cm/cm³) and can form a connected network with a cell ∼30 nm in size in the sample. Foreign atoms and molecules can migrate through channels of this network.