Highly Aligned α-Type Copper Phthalocyanine Formed on Rubbed Polyimide Alignment Layer

We have fabricated oriented copper-phthalocyanine (CuPc) films by vacuum deposition on rubbed polyimide (PI) alignment layers. It was found that the b-axis of α-type CuPc microcrystals changes its direction depending on the thickness of PI layers, namely, the b-axis is perpendicular to the rubbing direction on a thin rubbed PI layer but is almost perfectly aligned to the rubbing direction on a thick rubbed PI layer. The oriented structure on a thick PI layer was confirmed by a high dichroic ratio of about 4, which is expected in the optical absorption of α-type CuPc, and by highly oriented needle-shaped microcrystals observed by atomic force microscopy.