Induction of Cholesteric Mesophases by Simple Cyclic Derivatives of p,p'-Disubstituted 1,2-Diphenylethane-1,2-diols: Importance of Shape and Polarizability Effects.

A systematic study of the cholesteric induction in nematic solvents (MBBA and E7) by some cyclic derivatives of unsubstituted and p,p'-disubstituted-1,2-diphenylethane-1,2-diols shows that the values of the twisting power are significantly dependent on the nature of the link connecting the two oxygen atoms and on the nature of the p,p'-substituents. This result has been interpreted considering that the nature of the bridge affects the overall molecular shape and the p,p'-substituents affect both the molecular polarizability and shape. This investigation points out that the polarizability of the solute and the solvent is the main parameter in determining the value of the twisting power while electrostatic arene-arene interactions contribute to a less extent. It has been also observed that solutes having the same structure and the same absolute configuration can induce cholesteric helix of opposite sign depending on the substituent on the aromatic ring. This finding indicates that configurational assignments by cholesteric induction are reliable only if high values of twisting power are measured.