Eur. Phys. J. E 5, 589-598 (2001)
Helical twisting power and circular dichroism in nematic liquid crystals doped with chiral molecules
M.A. Osipov1 and H.-G. Kuball21 Department of Mathematics, University of Strathclyde, Glasgow G1 1XH, Scotland, UK
2 Universität Kaiserslautern, FB Chemie, 67653 Kaiserslautern, Germany
aas00107@maths.strath.ac.uk
(Received 9 May 2000 and Received in final form 6 June 2001)
Abstract
Explicit expressions for the helical twisting power of a chiral dopant in the
nematic phase have been obtained in the mean field approximation taking into
account chiral dispersion intermolecular interactions.
The results of the theory enable one to explain a correlation
between the signs of helical twisting power and circular dichroism of selected electronic transitions
which have
recently been established experimentally for some mono- and
bis-aminoantroquinones.
Helical twisting
power is proportional to the pseudoscalar parameter that
specifies
the chirality of the dopant molecule in terms of its dipole and quadrupole
matrix elements. This expression is simplified for a special class of
molecules in which chirality is induced by a perturbing achiral group
into an achiral skeleton. In this case
both helical twisting power and circular dichroism are
approximately
proportional to some simple pseudoscalar functions that specify the location
of the achiral perturbing group with respect to the symmetry planes of the
unperturbed
achiral skeleton. Simple sector rules have been proposed to
determine the sign change
of the helical twisting power associated with the change of location of the
perturbing group.
61.30.Cz - Molecular and microscopic models and theories of liquid crystal structure.
33.15.Bh - General molecular conformation and symmetry; stereochemistry.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001
