Han Jie, Chui Stephen Sin-Yin, Che Chi-Ming
Department of Chemistry and the HKU-CAS Joint Laboratory on New Materials, The University of Hong Kong, Pokfulam Road, Hong Kong, China.
Chem Asian J. 2006 Dec 18;1(6):814-25. doi: 10.1002/asia.200600252.
A class of extended 2,5-disubstituted-1,3,4-oxadiazoles R1-C6H4-{OC2N2}-C6H4-R2 (R1 = R2 = C10H21O 1 a, p-C10H21O-C6H4-C[triple bond]C 3 a, p-CH3O-C6H4-C[triple bond]C 3 b; R1 = C10H21O, R2 = CH3O 1 b, (CH3)2N 1 c; F 1 d; R1 = C10H21O-C6H4-C[triple bond]C, R2 = C10H21O 2 a, CH3O 2 b, (CH3)2N 2 c, F 2 d) were prepared, and their liquid-crystalline properties were examined. In CH2Cl2 solution, these compounds displayed a room-temperature emission with lambda(max) at 340-471 nm and quantum yields of 0.73-0.97. Compounds 1 d, 2 a-2 d, and 3 a exhibited various thermotropic mesophases (monotropic, enantiotropic nematic/smectic), which were examined by polarized-light optical microscopy and differential scanning calorimetry. Structure determination by a direct-space approach using simulated annealing or parallel tempering of the powder X-ray diffraction data revealed distinctive crystal-packing arrangements for mesogenic molecules 2 b and 3 a, leading to different nematic mesophase behavior, with 2 b being monotropic and 3 a enantiotropic in the narrow temperature range of 200-210 degrees C. The structural transitions associated with these crystalline solids and their mesophases were studied by variable-temperature X-ray diffractometry. Nondestructive phase transitions (crystal-to-crystal, crystal-to-mesophase, mesophase-to-liquid) were observed in the diffractograms of 1 b, 1 d, 2 b, 2 d, and 3 a measured at 25-200 degrees C. Powder X-ray diffraction and small-angle X-ray scattering data revealed that the structure of the annealed solid residue 2 b reverted to its original crystal/molecular packing when the isotropic liquid was cooled to room temperature. Structure-property relationships within these mesomorphic solids are discussed in the context of their molecular structures and intermolecular interactions.
制备了一类扩展的2,5-二取代-1,3,4-恶二唑R1-C6H4-{OC2N2}-C6H4-R2（R1 = R2 = C10H21O 1a，对-C10H21O-C6H4-C≡C 3a，对-CH3O-C6H4-C≡C 3b；R1 = C10H21O，R2 = CH3O 1b，(CH3)2N 1c；F 1d；R1 = C10H21O-C6H4-C≡C，R2 = C10H21O 2a，CH3O 2b，(CH3)2N 2c，F 2d），并研究了它们的液晶性质。在二氯甲烷溶液中，这些化合物在室温下发射，λ(max)在340 - 471 nm，量子产率为0.73 - 0.97。化合物1d、2a - 2d和3a呈现出各种热致中间相（单向性、双向性向列相/近晶相），通过偏光光学显微镜和差示扫描量热法对其进行了研究。使用粉末X射线衍射数据的模拟退火或并行回火通过直接空间方法进行结构测定，揭示了介晶分子2b和3a独特的晶体堆积排列，导致不同的向列相中间相行为，在200 - 210℃的狭窄温度范围内，2b为单向性，3a为双向性。通过变温X射线衍射法研究了与这些晶体固体及其中间相相关的结构转变。在25 - 200℃测量的1b、1d、2b、2d和3a的衍射图中观察到无损相变（晶体到晶体、晶体到中间相、中间相到液体）。粉末X射线衍射和小角X射线散射数据表明，当各向同性液体冷却至室温时，退火后的固体残余物2b的结构恢复到其原始晶体/分子堆积。在这些介晶固体的分子结构和分子间相互作用的背景下讨论了结构 - 性质关系。
