Polyfluorenes (PFO) derivatives, containing different ratios of heterocyclic, electron-withdrawing benzo[c]cinnoline moieties, BF10, BF25, and BF50 were synthesized by Suzuki coupling reaction. Photoluminescence (PL) spectra showed red-shifted emission peaks at around 500 nm for dilute polymer solutions and at around 530 nm for film samples. The PL quantum yields of polymer dilute solutions decreased as the ratios of benzo [c] cinnoline moieties in main chain increased. By UV irradiation (352 nm), the PL intensity of dilute polymer solutions was enhanced. The PL emission enhancement was attributed to the shorter conjugated length and the reduced donor acceptor interaction caused by oxygen-containing groups that were formed on fluorene moieties by UV irradiation. The enhanced emission could be quenched further by the addition of proton donors such as trifluoroacetic acid. The completely alternating polymer BF50 consisting of fluorene and benzo[c]cinnoline moieties in dilute THF solution showed a linear relationship between UV doses and PL quantum yields after UV irradiation. It exhibited good potential for UV-sensing applications.