Excellent uniaxial alignment of poly(9,9-dioctylfluorenyl-2,7-diyl) induced by photoaligned polyimide films

Abstract

We have investigated the alignment of poly (9,9-dioctylfluorenyl-2,7-diyl) (PFO) induced by photoaligned polyimide films. To induce anisotropic orientation of polyimide backbone structures by optical treatment, we used a specially designed polyimide (Azo-PI), which contains azobenzene in the backbone structure. The 30-nm-thick PFO layer, spincoated onto a photoaligned Azo-PI film, was heated to the liquid crystalline phase of PFO, and then cooled down to room temperature at -0.1 ℃/min. The thermally treated PFO layer showed a polarization ratio of approximately 30 in photoluminescence. This high polarization ratio has not previously been reported in PFO films formed by other alignment techniques. This result indicates that the photoaligned Azo-PI film has an excellent ability to align liquid crystalline polymers