A heterocyclic oligomer, thieno[3,2-b]thiophene (TT) end-capped famous 3,4-ethylenedioxythiophene (EDOT) unit and their electrosynthesized polymer P(TT-EDOT-TT) have been facilely achieved. To in-depth understand the effects of structural modification on physico-chemical properties and electrochromic performances of monomers and/or polymers, the absorption spectroscopy, electrochemistry, micromorphology, and spectroelectrochemistry were systematically studied. In contrast to TT and EDOT, TT-EDOT-TT possessed extended pi-conjugation and narrowed band gap in molecular level. Through carefully comparison with PIT, it has been found that the electrochromic performances of PITT-EDOT-TT) film exhibited much higher optical contrast (69%, while 3% for PIT in the near-infrared region) and superior coloring efficiency (255.3 cm(2) C-1, while 36.8 cm(2) C-1 for PIT), and switching times (within 1 s, while more than 9 s for PIT). Notably, PITT-EDOT-TT) film can achieve the mutual conversion between RGB primary colors (red-green-blue) under variable voltages, which hold quite promising for display applications.