Soluble pi -conjugated polythiophene derivatives containing the electron-transporting moiety were synthesized through FeCl3-oxidative polymerization; poly( 3-(2-benzotriazoloethyl)thiophene)(PBET) and poly(3-(2-(5-chlorobenzotriazolo)ethyl)thiophene) (PCBET). The structure of the polymers was verified by FT-IR, H-1 NMR, and element analysis. Introduction of the electron-transporting moiety, benzotriazole, on the side chain in poly(3-alkylthiophene) was an attempt to balance the injection rates of the electron and the hole from the opposite electrode into the light-emitting diodes (LEDs). This modification, therefore, would enhance electroluminescence (EL) efficiency. As the result, the external EL quantum efficiencies of PBET and PCBET were 7 and 3 times higher than that of poly(3-octylthiophene) (POT).