A series of novel asymmetrical fused compounds containing the backbone of fluorene[2,3-b]benzo[d]thiophene (FBT) were effectively synthesized and fully characterized. Single-crystal X-ray studies demonstrated that the length of the substituent side chains greatly affects the solid-state packing of the obtained fused compounds. DFT, photophysical, and electrochemical studies all showed that the FBTs have large band gaps, low-lying HOMO energy levels, and therefore good stability toward oxidation. Moreover, the substituents strongly influence the fluorescence properties of the resulting FBT derivatives. The di-n-hexyl compound exhibits intense fluorescence in solution with the highest quantum yield of up to 91 %. Solution-processed green phosphorescent organic light-emitting diodes with the di-n-butyl derivative as the host material exhibited a maximum brightness of 14,185 cd m(-2) and a luminescence efficiency of 12 cd A(-1).