Characterization of liquid crystalline phthalocyanines for OFET applications

Liquid crystalline phthalocyanines, metalized and metal-free, were investigated in order to evaluate their applicability as semiconducting active layer in optoelectronic devices. They present a stable rectangular columnar plastic mesophase at room temperature after cooling down from the isotropic liquid. Previous studies demonstrated high rectification with moderate charge carrier mobility in a diode structure under unfavorable edge-on alignment, as a result of the strong pi-pi interactions exhibited by close molecular packing of the mesophase. The spontaneous dominant alignment of the columns parallel to the substrate is desired for application in field effect transistors. The optical, structural and morphological properties of the compounds in spin-coated films demonstrated potential for good charge transport in-plane direction. The output characteristics of a field effect transistor with the copper phthalocyanine are consistent with the literature, and could be improved by thermal treatment.