A fluorescent polythiophene derivative bearing a donor-acceptor dansyl substituent was prepared by a simple synthetic route. Poly[2-(3'-thienyl)ethyl dansylglycinate] (PTEDG) is soluble in common organic solvents which allow the drop cast of films onto ITO electrodes. The electrochromic properties of these films were investigated and it was observed color variation from yellow, in the neutral state, to bluish-gray, in the oxidized state. Both the monomer 2-(3'-thienyl)ethyl dansylglycinate (TEDG) and its polymer PTEDG are, respectively, green and yellow light emitter materials.