Role of local intermolecular contacts in the physical properties of induced helical phases based on nematic disubstituted azobenzene

Abstract

The mesomorphic, dielectric, orientational and rheological properties of the induced chiral nematic phase on the base of 4-butyl-4′-octanoyloxyazoxybenzene (C4-AB-OCOC7) doped with 1R(+)-1′,7′,7′-trimethylbicyclo[2.2.1]heptane[2′,3′-b]-2,3-dicyanopyrazine ((R + )CDCP) and (2R,3R)(−)2,3 butanediol (R-)BD were studied. The clearing temperatures and the pitch were measured, and the value of the helical twisting power were calculated. A strong influence of the dopants structure on the thermal stability of the spiral phase and the dielectric anisotropy was shown. An increase in the orientational order parameter LC upon doping with a chiral diol and the formation of its H-bond with the ester group of the terminal substituent were established by 1H NMR. Stable structures of dopant - LC solvates, their dipole moments, anisotropy of polarizability and formation energy have been established by DFT simulation. The determining influence of local dipole–dipole contacts and H-bonds on the structure and properties of solvates has been substantiated. The calculated data allowed to establish the reasons for the effect of dopants on the physical properties of the spiral phases. The effect of (2R, 3R) (-) 2,3 butanediol on the kinematic viscosity of two nematic solvents - C4-AB-OCOC7 and a binary mixture of alkoxycyanobiphenyls (CB-2) was investigated. The influence of the dopant was shown to be determined by the geometry of solvates formed due to local H-bonds with electron-donor moieties of nematic solvents.