Effect of different π bridges on electro-optic properties of D-A-D type conjugated polymers based on nitro-substituted triphenylamine derivatives

We designed and synthesized two monomers, TTTPA and TETPA, by inserting the EDOT and thiophene unit as π-bridges between thiophene unit and nitro-substituted triphenylamine (TPA) through Stille coupling reaction, and the corresponding polymers PTTTPA and PTETPA were also prepared by electrochemical polymerization. Both TTTPA and TETPA displayed the red-shifted absorption spectra and lower onset oxidation potential, in particular, TETPA possessed a much lower initial oxidation potential of 0.68 V than its counterpart TTPA (1.00 V) without π-bridges. In addition, PTTTPA possessed the reversible and stable color change from yellow to gray between the neutral and oxidized state with a higher optical contrast of 27.1%, and exhibited a higher coloration efficiency of 134.43 cm² C^-1 when compared with PTTPA and PTETPA. These results demonstrated that the reasonable introduction of π-bridges could optimize the electrochromic performance of TPA-based polymer.