New copolyfluorenes containing 4,7-di-2-thienyl-2,1,3-benzothiadiazole and 2,1,3-benzothiadiazole or derivatives of naphthalimide as luminophores were synthesized under microwave heating. Charge-transporting carbazole, triphenylamine, or diphenyloxadiazole groups were introduced into the side chains of polymers through 9,9-bis-(4-phenoxy)-2,7-fluorene units. Copolyfluorenes were also modified via insertion of 10 mol% of 2,7-[9,9-bis-(6′-diethoxyphosphorylhexyl)]fluorene or dibenzothiophene-S,S-dioxide comonomer units into the polymer backbone. This study demonstrates the influence of chemical compositions, molecular masses of the polymers under investigation, and thermal treatment on microstructures of their films. Photo- and electroluminescent characteristics of the synthesized copolyfluorenes were determined. The best samples of devices manifested the luminance of 5110 cd m⁻², the current efficiency of 1.33 cd A⁻¹, and the CIE 1931 xy chromaticity coordinates of (0.339 0.364), or 7930 cd m⁻², 2.18 cd A⁻¹, and of (0.300 0.369) respectively. The effect of active layer thickness on the white emission color of polymer light-emitting diodes was revealed.