Nitrile vibrations as reporters of field-induced phase transitions in 4-cyano-4'-pentylbiphenyl (5CB).
4-Cyano-4'-pentylbiphenyl (5CB) is a liquid crystal forming compound with a terminal nitrile group aligned with the long axis of the molecule. Simulations of condensed-phase 5CB were carried out both with and without applied electric fields to provide an understanding of the Stark shift of the terminal nitrile group. A field-induced isotropic-nematic phase transition was observed in the simulations, and the effects of this transition on the distribution of nitrile frequencies were computed. Classical bond displacement correlation functions exhibit a ∼2.3 cm(-1) red-shift of a portion of the main nitrile peak, and this shift was observed only when the fields were large enough to induce orientational ordering of the bulk phase. Distributions of frequencies obtained via cluster-based fits to quantum mechanical energies of nitrile bond deformations exhibit a similar ∼2.7 cm(-1) red-shift. Joint spatial-angular distribution functions indicate that phase-induced anticaging of the nitrile bond is contributing to the change in the nitrile spectrum.
Department of Chemistry and Biochemistry, University of Notre Dame , 251 Nieuwland Science Hall, Notre Dame, Indiana 46556, United States.
James M
JM
Marr
J Daniel
JD
Gezelter