Absorption and emission dichroism of polyethylene films with molecularly dispersed push-pull terthiophenes

Substituted terthiophenes act as excellent chromophores for linear polarizers based on oriented polyethylene thin films. The dispersibility in the polymer matrix exerts a determining role on the optical performances. The modulation of the crystallization of the dye by attaching to the chromophoric moiety different linear or branched alkyl chains and by varying the polyethylene disordered phase (from UHMWPE to LLDPE) allows to obtain different extent of molecular dispersion. Scanning electron microscopy (SEM) and x-ray microanalysis help in determining the detailed morphology of the binary blend films. After uniaxial stretching, the films from molecularly dispersed dyes show excellent dichroic properties in absorption with dichroic ratios up to 60. On the contrary, the anisotropy in emission of the same films is lower than for the corresponding films from more aggregated dyes owing to the more effective depolarization phenomena.