1IntroductionThere has been wide interest in the photophysical properties of rod-like fluorene based conjugated polymers because of their potential applications in various optoelectronic devices, especially in polymers light-emitting diodes (PLEDs)[1]. In this work, a series of fluorene-alt-benzene based conjugated main chain polymers with different length alkyl side chains on phenylene ring were designed and successfully synthesized. The effect of alkyl chain length on the photophysical property, phase transition behavior and morphology structure of the polymers were investigated.