Reorientation behaviour of bent core molecules in response to an external electric field as detected by time-resolved FTIR spectroscopy

Time-resolved polarized Fourier transform infrared spectroscopy (FTIR) is e mployed to analyse the segmental orientation and mobility of achiral bent c ore molecules in response to an external electric field. By shearing the su bstance between ITO coated CaF2 windows two types of domain, racemic and ho mochiral, are formed in the high temperature B-2 phase. Each of these domai ns is characterized by two spontaneous symmetry-breaking instabilities whic h yield a symmetric and an antisymmetric electro-optical response, respecti vely. Taking advantage of the specificity of IR spectroscopy, this switchin g behaviour is analysed on a molecular level for the moieties of the bent c ore liquid crystal materials. In this way, the electrically induced reorien tation of the different segments on a cone and the suppression of the antif erroelectric structure at higher frequencies can be followed in detail. Fur thermore the biased rotation of the two carbonyl groups around the molecula r long axis is determined. It is shown that all molecular units move synchr onously on the time scale of the experiment (10 mu s).