Steric Hindrance Influence of a Diazo Link upon Mesogenic Properties of some Ligands and Related Copper Complexes
Résumé
Some new polymethylated compounds containing three rings and four rings have been synthetized. The crystalline structures of 2,3-dimethyl-4-ethyloxbenzyloxy-4'-(4-methoxysalicylaldimine)-azobenzene (DIM ) and 2,3,6-trimerhyl-4-metÉylbènzoyloxy-4'-butylazobenzene (TRIM) are described. Due to large steric interactions, the diazo linkage make sa 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-13C chemical shifts, molecular rmodeliing and transition temperatures Ty. For the three rngs core, the thermal stability of the mesophase decreases with substitution pattern dissymetry.The effect of the conjugation loss is evidenced by the decrease of TN versus the carbon number within the chain. For the four rings core, the effect on the transition temperatures of polymethylatedl igands is nearly independent of the length of the mesogenicc ore and dependso nly on the lateral substituentp ositionsw ithin the core. For the related copper complexes, the Tm transition temperatures exhibit a small dependence upon the methyl substitution.