Polyimide Photo-Alignment Films Applicable to Poly[(9,9-Dioctylfluorenyl-2,7-Diyl)-Co-Bithiophene]

We have succeeded in forming highly oriented poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2) layers by using photo-aligned polyimide films. The polyimide (Azo-PI) contains azobenzene in the backbone structure, which allows us to optically control the alignment of the backbone structure. The photo-aligned Azo-PI films were stable to xylene (a solvent of F8T2) and to annealing at a liquid-crystalline temperature of F8T2. After annealing at 285°C for 15 min followed by quenching to room temperature, the ∼20 nm-thick F8T2 layer on the photo-aligned Azo-PI film showed a dichroic ratio of ∼14 at 490 nm (the absorption maximum), indicative of a high degree of alignment of F8T2. We conclude that the photo-aligned Azo-PI films are proper alignment films for F8T2.

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