High Morphological Stability Research Articles

Modulation of Physical Properties of Ter(9,9-ditolylfluorene) by Backbone-Embedded Heteroarenes

[structure: see text] Novel ter(9,9-ditolylfluorene) analogues containing thiophene and pyridine rings embedded as functional constituents within the parent hydrocarbon backbone have been synthesized. These new molecules exhibit highly efficient photoluminescence and high thermal and morphological stability. The electronic structure of the terfluorene backbone is significantly perturbed, which allows modulation of the backbone energy levels.

Influence of interfaces on the storage of ion-implanted He in multilayered metallic composites

We studied ion beam mixing and He accumulation in Cu∕Nb multilayer thin films after 33keV He implantation at room temperature to a dose of 1.5×1017atoms∕cm2. Multilayered thin films consisting of alternating Cu and Nb layers were produced by magnetron sputtering. Two types of samples, one with an individual layer thickness of 4nm and another with 40nm were examined. The Cu∕Nb samples were analyzed in the as-deposited state, after He ion implantation, as well as after post-implantation annealing. The ion beam mixing of the interface structure was monitored by Rutherford backscattering spectrometry and cross-section transmission electron microscopy imaging. Elastic recoil detection analysis was performed to examine the helium concentration depth distribution. Scanning electron microscopy was employed to investigate He blister formation upon annealing. A comparison of the results deduced from the methods listed above reveals a very high morphological stability of the nanolayered structure. The nanolayered structure of the Cu∕Nb multilayer thin films is retained. He bubbles were observed to reside within the layers but more so at the Cu∕Nb incoherent interfaces.

Novel Stable Blue-Light-Emitting Oligofluorene Networks Immobilized by Boronic Acid Anhydride Linkages

Thermal dehydration of boronic acid groups to form six-membered boronic acid anhydride (boroxine) was employed as a means of immobilizing oligofluorenes. This approach appears to improve the photoluminescenct stability of the cross-linked films compared to polyfluorenes. The emergence of long-wavelength emission upon thermal treatment usually observed in polyfluorenes has been prevented in this system. Initially the fluorene dimer (F2BA), trimer (F3BA), and tetramer (F4BA) containing boronic acid groups were prepared. These compounds were found to be readily soluble in common solvents such as THF, acetone, and DMF. Transparent thin films of these materials could be easily prepared by casting their solutions in THF onto KBr disks or glass substrates. Using mild reaction conditions (60−130 °C under vacuum for 2 h), these oligomers in the solid sate readily undergo cross-linking reactions by the dehydration of boronic acid groups as evidenced by FT-IR spectroscopy and DSC/TGA studies. The resulting cross-linked amorphous networks exhibit high thermal (Td at 5% weight loss, 363−420 °C) and morphological (Tg, 173−202 °C) stability. Under UV irradiation, these compounds emit bright violet-blue (F2BA) and blue (F3BA and F4BA) light both in solution and in the solid state. The cured films exhibited almost identical UV−vis and fluorescence spectra even after heating at 150 °C for 24 h, showing no long wavelength emission. The fabrication of LED devices using F3BA or F4BA as the light-emitting layer and a carbazole diboronic acid (CzBA) as the hole-transporting layer demonstrated that these thermally curable diboronic acids can be used to achieve double- (or multi-) layered configurations.

Synthesis and characterization of new oxadiazoleamine based spiro-linked fluorescence dyes

We present the synthesis and characterization of a new class of bipolar compounds based on unsymmetrically substituted spirobifluorenes intended as active materials for organic light emitting devices. The compounds are essentially based on a center core of spirobifluorene equipped with electron-donating oxadiazole-groups in the 2 and 2′ and electron-accepting diphenylamine-groups in the 7- and 7′-position. All compounds can be processed into thin amorphous films with high morphologic stability by simple spin coating from solutions in organic solvents and show intense fluorescence in solution as well as in the solid state. The emission range of the resulting dyes can be tuned in the range between 370 and 540 nm by varying the conjugated system or changing the strength of the acceptor and donor moieties.

Synthesis and properties of novel thiophene-based conjugated homologues: 9,9-diphenylfluorene-capped oligothiophenes.

[reaction: see text] A series of novel 9,9-diarylfluorene-capped oligothiophenes were synthesized by Suzuki coupling reactions in good yields. The color of the emissions can be controlled by varying the conjugation length of the oligothiophene core. The bulky and rigid terminal groups of the resulting oligomers are significantly beneficial for their high morphological and thermal stability. These new oligothiophenes exhibit intriguing reversible oxidation and reduction redox behavior.

Structural and Morphological Observations on Tungsten Oxide Hydrates Ged to Room Temperature in Alkali Containing Queous Environment

The room temperature ageing process of tungsten oxide hydrate (H2WO4.H2O) grains prepared by the methods of Freedman [J. Am. Chem. Soc. 81 (1959) 3834.] ([Na]residual 10ppm)) and Zocher and Jacobson [Kolloidchem. Beih. 28-6 (1929) 167.] ([Na]residual 100ppm) has been studied. A comparison between two preparation methods and ageing characteristics is given. It is found that spindle shaped - Zocher type grains have a strong tendency to morphological conversion depending on pH value of surrounding aqueous solution. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) studies have shown that the high structural and morphological stability of Freedman type grains can be altered by presence of alkali ions. Moreover, some incorporation of cations was observed.

Growth of large ZnSe single crystal by CVT method

The growth of ZnSe single crystals by chemical vapor transport (CVT) method using iodine as transport agent was investigated for the purpose of growing a large ZnSe crystal with a diameter of 1 in. The optimum growth temperature, seed orientation associated with the angle at the conical tip and iodine concentration were determined from the viewpoint of high growth rate and morphological stability. A 1″∅ ZnSe single crystal was successfully grown under determined growth conditions.

Spiro linked compounds for use as active materials in organic light emitting diodes

AbstractSpiro‐linkage of low molecular weight entities as a new structural concept for the design of new active materials for electroluminescent applications is presented. These spiro linked compounds result in nonpolymeric organic glasses with high thermal stability as can be derived from their high glass transition temperatures (Tg), and characterized by differential scanning calorimetry. Blue emitters based on spiro linked oligophenyles are presented. These compounds are soluble in common organic solvents and show high photoluminescence quantum efficiency in the solid state and high morphologic stability with glass transition temperatures up to 250°C. Charge transport materials based on spiro linked versions of 2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole (PBD) for electron transport, and spiro linked versions of triphenyldiamin derivatives (TPD) for hole transport show improved morphologic properties with nearly unchanged electronic properties compared to the parent compounds.High quality amorphous films can be prepared with the spiro compounds by vapor deposition as well as by simple spin coating.

Low molecular organic glasses for blue electroluminescence

Spiro-linkage is used to modify the steric demand of low molecular organic compounds to improve their processability and morphologic stability, while their electronic properties are retained. These spiro-linked compounds form stable nonpolymeric organic glasses with high glass transition temperatures, usually associated with amorphous polymers. High quality amorphous films with high morphologic stability can be prepared with these spiro-linked luminescent or charge transport materials by conventional spin-coating techniques as well as by vapor deposition. Based on these spiro-compounds, blue electroluminescence devices with high color purity, high brightness and low turn-on voltage are presented. A blue light-emitting two-layer device, fabricated by combining a hole transporting spiro-TAD with an electron transporting spiro-PBD, shows a turn-on voltage at 2.7 V and a luminance of 500 cd/m 2 at 5 V.

On the development of proton conducting materials for technological applications

Some aspects of the simultaneous optimisation of material properties of proton conductors which are relevant for their use in electrochemical cells such as fuel cells, electrochemical reactors and sensors (high proton conductivity, chemical, electrochemical and morphological stability) are discussed. Suggestions are made for the further development of proton conducting perovskite type oxides, proton conducting polymer membranes and medium temperature proton conducting materials.