Chiroptical Properties of Terthiophene Chromophores Dispersed in Oriented and Unoriented Polyethylene Films

Two new chiral terthiophene chromophores II and III were prepared with 99% enantiomeric excess. Chiro- ptical properties of these dyes dispersed in ultra high molec- ular weight polyethylene (UHMWPE) films were determined and compared with the same properties in solution. In the solid state, the optical activity strongly depends on the inter- action mechanisms within small crystalline aggregates of chromophores. The film morphology and chromophore dis- persion were also investigated by scanning electron micro- scopy (SEM) and differential scanning calorimetry (DSC). The good correlation between chromophore aggregation and chiroptical activity of the binary films promotes circular dichroism (CD) as an effective technique for monitoring the phase dispersion behaviour of dichroic dyes into polymer matrices. By mechanical stretching of the film a linearly dichroic orientation of the chromophores is obtained which results in a high degree of linear dichroism. The influence of the uniaxial orientation of terthiophene molecules along the drawing direction of UHMWPE on the chiroptical properties of the films, and the possible application of the oriented devi- ces as linear polarizers are discussed.