Novel fluorene-based blue-light-emitting copolymers with an ultraviolet-blue-light (UV-blue-light) emitting host and a blue-light emitting component, 4-N,N-diphenylaminostilbene (DPS) have been designed and synthesized by using the palladium- catalyzed Suzuki coupling reaction. It was found that both copolymers poly [2,7-(9,9-dioctylfluorene)-alt-1,3-(5-carbazolphenylene)] (PFCz) DPS1 and PFCz-DPS1-OXD show pure blue-light emission even with only 1 % DPS units because of the efficient energy transfer from the UV-blue-light emitting PFCz segments to the blue-light-emitting DPS units. Moreover, because of the efficient energy transfer/charge trapping in these copolymers, PFCz-DPS1 and PFCz-DPS1-OXD show excellent device performance with a very stable pure blue-light emission. By using a neutral surfactant poly[9,9-bis(6'-(diethanolamino)hexyl)-fluorene] (PFN-OH) as the electron injection layer, the device based on PFCz-DPS1-OXD5 with the configuration of ITO/PEDOT:PSS/PVK/polymer/PFN-OH/Al showed a maximum quantum efficiency of 2.83 % and a maximum luminous efficiency of 2.50 cd A–1. Its CIE 1931 chromaticity coordinates of (0.156, 0.080) match very well with the NTSC standard blue pixel coordinates of (0.14, 0.08). These results indicate that this kind of dopant/host copolymer could be a promising candidate for blue-light-emitting polymers with high efficiency, good color purity, and excellent color stability.