103761-99-5Relevant academic research and scientific papers
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 (2000)
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.
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.
