Nematic liquid crystal alignment on phthalocyanine LB films

Two newly synthesized phthalocyanine compounds' Langmuir-Blodgett (LB) films were fabricated to align nematic liquid crystal(LC). Optical spectra were used to characterize the films and antiparallel type LC cells were constructed adopting SnPc and VOPc LB films as aligning layers. We found that LC molecules would align homogeneously on SnPc LB films along the deposition direction while those of on VOPc LB films align obliquely. The electrooptic effects of the cells were investigated and they showed an in agreement with LC alignment configurations. A TN type cell using SnPc LB films as aligning layer was also investigated. It has a better electrooptic effect than the antiparallel type. Since the two phthalocyanine compounds have a similar molecular structure but with different complex metals, and the corresponding LB films orient with the nearly same orientation angle on the substrates, ignoring other interactions, we think the alignment mechanism that results in different alignment configurations may be concerned with the interaction between LC molecules and oxygen atoms that are out of the macrocycle planes in VOPc LB films.