Steric hindrance influence of a diazo link upon mesogenic properties of some ligands and related copper complexes
作者:P Lesot、F Perez、P Judeinstein、JP Bayle、H Allouchi、M Cotrait
DOI:10.1051/jcp/1997941695
日期:——
Some new polymethylated compounds containing three rings and four rings have been synthetized. The crystalline structures of 2,3-dimethyl-4-ethoxy benzoyloxy- 4'-(4-methoxysalicylaldimine)-azobenzene (DIM) and 2,3,6-trimethyl-4-methylben zoyloxy-4'-butylazobenzene (TRIM) are described. Due to larger steric interactions, the diazo linkage makes a larger dihedral angle in TRIM than in DIM. The effect of steric hindrance of the diazo linkage upon the mesophase stability is discussed by the use of isotropic Carbon-13 chemical shifts, molecular modelling and transition temperatures, TNI. For the three rings core, the thermal stability of the mesophase decreases with substitution pattern dissymetry. The effect of the conjugation loss is evidenced by the decrease of TNI versus the carbon number within the chain. For the four rings core, the effect on the transition temperatures of polymethylated ligands is nearly independent of the length of the mesogenic core and depends only on the lateral substituent positions within the core. For the related copper complexes, the TNI transition temperatures exhibit a small dependence upon the methyl substitution.
一些含有三环和四环的新型多甲基化化合物已被合成。描述了2,3-二甲基-4-乙氧基苯甲氧基-4'-(4-甲氧基水杨醛亚胺)-偶氮苯(DIM)和2,3,6-三甲基-4-甲基苯甲氧基-4'-丁基偶氮苯(TRIM)的结晶结构。由于更大的立体相互作用,TRIM中的二氮连接使二面角比DIM中的更大。通过使用各向同性碳-13化学位移、分子建模和转变温度TNI讨论了二氮连接的立体障碍对介相稳定性的影响。对于三环核心,介相的热稳定性随着取代模式的不对称性而降低。共轭丧失的影响体现在随着链中碳数的增加,TNI的降低。对于四环核心,聚甲基化配体的转变温度对介生核心的长度几乎不依赖,仅取决于核心内侧基团的位置。对于相关的铜络合物,TNI转变温度对甲基取代显示出小的依赖性。