201022-14-2Relevant academic research and scientific papers
Synthesis of a polyoxadiazole containing the 4-hydroxypyridine group and photo-induced fluorescent imaging on the polymer film
Kim, Young-shin,Kim, Dai Geun,Kwon, Na Young,Kim, Hyung Jun,Choi, Moon Soo,Lee, Minjung,Lee, Taek Seung
experimental part, p. 223 - 229 (2011/10/09)
A polyoxadiazole containing the 4-hydroxypyridine group, introduced to enhance the intermolecular interaction between polymer chains as well as for photosensitization, was synthesized from a corresponding precursor polyhydrazide. The absorption and emission spectra of the polymer film exhibited red-shifted maxima compared to those of the polyoxadiazole in chloroform solution, indicative of the presence of significant intermolecular interactions. The synthesized polymer showed a unique fluorescence enhancement upon UV irradiation in solution as well as in the film, presumably due to the photosensitized oxidation of hydroxypyridine groups to produce pyridone structures having different intermolecular interactions. Thus, this phenomenon enabled us to obtain a stable patterned image with enhanced fluorescence intensity in the UV-exposed area of the polymer film without any subsequent processes such as baking or etching.
Synthesis and characterization of 1,3,4-oxadiazole derivatives containing alkoxy chains with different lengths
Zhang, Xiao-bing,Tang, Ben-chen,Zhang, Peng,Li, Min,Tian, Wen-jing
, p. 55 - 64 (2008/03/13)
The synthesis, optical properties, electrochemical properties, electronic structures and applications in electroluminescent device of three series of 1,3,4-oxadiazole derivatives, 1,4-bis[(4-methylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD1), 5,5′-di-(4-methyl)-2,2′-p-(2,5-bisalkoxyphenylene)-bis-1,3,4 -oxadiazole (OXD2-n) and 1,4-bis[(4-alkoxyphenyl)-1,3,4-oxadiazolyl]phenylene (OXD3-n) are reported. The molecular structures of the oxadiazole compounds were confirmed by FT-IR, 1H NMR spectroscopy and elemental analysis. The optical and electrochemical properties of the compounds were investigated by UV-vis absorption and photoluminescence spectroscopy as well as cyclic voltammetry. The results show that introduction of two alkoxy groups whose electron-donating ability is stronger than that of methyl groups increases the electron density of the conjugated segment of OXD2-n (with side-on alkoxy substituents) and OXD3-n (with end-on alkoxy substituents), and thus leads to the absorption maximum bathochromic-shift compared to that of OXD1. The HOMO and LUMO energy levels of the compounds studied are in the range of -2.78 to -2.89 and -5.75 to -6.20 eV. Calculations on the representative compounds by the Dmol3 package of MS Modeling 3.0 revealed that the increase of energy levels in both OXD2-n and OXD3-n was due to the change of the frontier molecular orbital distribution in the central benzene ring. The light-emitting devices have been fabricated using blends of MEH-PPV and these compounds as emissive layers, among which, maximum brightness up to 11810 cd m-2 (8.5 V) has been observed, which is 40 times brighter than that with MEH-PPV. The result of the devices suggested that oxadiazole derivatives studied function well as electron-transporting materials and can be used in LEDs, and thus to enhance the efficiency of LEDs.
Design principles to tune the optical properties of 1,3,4-oxadiazole- containing molecules
Bolton, Onas,Kim, Jinsang
, p. 1981 - 1988 (2008/02/08)
We have synthesized a series of oxadiazole compounds and ethynylene analogs. Our data reveal that the ring is both optically transparent in the visible range and fully conjugating while we have also discovered the presence of a non-radiative mechanism active in molecules containing common para-dialkoxy substituents adjacent to the oxadiazole ring(s). This structure leads to a greatly reduced quantum yield, in our example dropping from 95.0% to 48.0%. Through our thorough study we have revealed evidence that this is the result of a repulsive interaction between the oxadiazole and the adjacent alkoxy oxygen atom, which we believe prevents excited-state planarity. This quantum yield reduction is preventable through the design principles presented here. The Royal Society of Chemistry 2007.
Thermochromism of a liquid crystalline dialkoxy substituted poly(1,4-phenylene-1,3,4-oxadiazol-2,5-diyl)
Thunemann,Janietz,Anlauf,Wedel
, p. 2652 - 2656 (2007/10/03)
The thermotropic liquid crystalline behavior of poly[2',5'-bis(hexadecyloxy)-1,4-phenylene-1,3,4-oxadiazol-2,5-diyl] C16pod was investigated using differential scanning calorimetry, small- and wide-angle X-ray scattering techniques. An order-order transition was found at about 120 °C, which was attributed to the transition from a smectic H phase at a low temperature to a smectic A phase at a high temperature. The repeat unit of the smectic H phase is d = 3.70 nm which is composed of a polymer-rich layer (d1 = 1.70 nm) and an alkyl chain rich layer (d2 = 2.00 nm). For the smectic A phase we calculated d = 3.85 nm, d1 = 1.75 nm and d2 = 2.10 nm. The lamellae of the smectic A phase are assumed to show undulations with a periodicity of 6.3 nm. By contrast, the smectic H phase has no periodic undulations. The C16pod changes its color from yellow-green at 25 °C to blue at 130 °C. UV-vis and fluorescence spectroscopy were used for a quantitative determination of the thermochromicity of C16pod. It was found that the optical properties change continuously within a temperature range of 25 to 140 °C. Even at the order-order transition the UV-vis and fluorescence intensities change continuously. It was therefore concluded that the effective conjugation length of the C16pod reduces continuously with increasing temperature. The order-order transition is caused predominantly by the melting of the side-chains.
