化学学报 ›› 2007, Vol. 65 ›› Issue (15): 1454-1458. 上一篇    下一篇

研究论文

分子间氢键对苯并菲柱状介晶性的影响: 量子化学ONIOM (MO/MM)研究

丁涪江*, 赵可清   

  1. (四川师范大学化学与材料科学学院 成都 610066)
  • 投稿日期:2006-07-15 修回日期:2007-01-12 发布日期:2007-08-14
  • 通讯作者: 丁涪江

Effect of Intermolecular Hydrogen Bond on Mesogenic Behaviors of Triphenylene Derivatives: An Quantum Chemical ONIOM (MO/MM) Study

DING Fu-Jiang*; ZHAO Ke-Qing   

  1. (College of Chemistry and Material Science, Sichuan Normal University, Chengdu 610066)
  • Received:2006-07-15 Revised:2007-01-12 Published:2007-08-14
  • Contact: DING Fu-Jiang

我们最近的实验显示: 对于分子中含有酰胺基的苯并菲液晶化合物C18H6(OC5H11)3(OCH2CONHC4H9)3, 对称化合物有比反对称异构体更高的清亮点和更有序的六方柱状介晶相, 且与具有同样软链长度的分子中不含酰胺基的化合物C18H6(OC5H11)3(OCH2COOC4H9)3相比较, 有更高的清亮点和更丰富的柱状介晶相. 本文通过量子化学ONIOM (B3LYP/6-31G(d,p):UFF)计算, 说明对于带酰胺基的分子, 对称分子比反对称分子有较大的稳定化能和较高的转动势垒. 对于对称性分子, 带酰胺基的分子比带酯基的分子有较大的稳定化能和较高的转动势垒. 这说明由酰胺基形成的分子间氢键起了稳定液晶相和锚定六方柱状相的作用, 可以解释带酰胺基的分子和对称性分子有较高的清亮点和更有序的六方柱状介晶相. 如果加长酰胺基的软链, 则可使氢键锚定的扭转角减少, 这样有利于提高电荷传输速率.

关键词: 苯并菲, 盘状液晶, 分子间氢键, ONIOM计算

According to our experimental studies for the triphenylene derivatives containing amide group with structure of C18H6(OC5H11)3(OCH2CONHC4H9)3, the symmetrical compounds exhibit higher clearing points and more orderred hexagonal columnar mesophase than their corresponding asymmetrical ones; and also than their corresponding symmetrical compounds containing ester group. To investigate both the hy-drogen bonding and the ordering in the symmetrical and asymmetrical triphenylene discotic liquid crystals, quantum chemical ONIOM (B3LYP(6-31G(d,p)∶UFF) calculations were performed on C18H6(OC2H5)3(OCH2CONHCH3)3 and C18H6(OC2H5)3(OCH2COOCH3)3. In the optimized structures of the dimers, the distances between the p-p stacked triphenylene cores are calculated to be about 0.35 nm, in good agreement with the experimental X-ray result. A C=O…H—N hydrogen bond is formed between two triphenylene derivatives containing amide group, which are optimized at r(N—H…O)=0.301 nm, a near-optimum length for such an H-bond. The results show that, for compounds containing amide group, the symmetrical compounds have bigger interaction energy and higher rotation energy barrier than their correcponding asymmetrical ones due to more H-bonds formation for the former. And the compounds containing amide group have bigger interac-tion energy and higher rotation energy barrier than ones containing ester group due to the formation of H-bonds for the former. We predict a significant increase in the charge mobility when going from C18H6(OC5H11)3(OCH2CONHC4H9)3 to C18H6(OC5H11)3(OC3H6CONHC4H9)3 because the rotational angle betwee two adjacent discs in the stack of the latter by optimizing is of 10.1°, which is much less than that of the former 42.6°.

Key words: triphenylene, discotic liquid crystal, intermolecular hydrogen bonding, ONIOM calculation