Electrochemical synthesis and characterization of polymers from bis(3,4-ethylenedioxythiophene)-thiophenes (BEDOT-Ts) and bis(3,4-ethylenedioxythiophene)-benzenes (BEDOT-Bs) as optoelectronic materials

A series of bis(3,4-ethylenedioxythiophene)-thiophene derivatives (BEDOT-Ts) and bis(3,4-ethylenedioxythiophene)-benzene derivatives (BEDOT-Bs) monomers were electrochemically polymerized onto glassy carbon or ITO-coated glass electrodes. Cyclic voltammetry (CV), infrared (IR), UV-vis-NIR and photoluminescence (PL) spectroscopy were employed to investigate and characterize properties of resulting polymers. dc-conductivities of these polymers were measured by the four-point probe method.;Cyclic voltammetry studies show that the redox half potentials of PBEDOT-3BT, PBEDOT-3OT, PBEDOT-3TBS and PBEDOT-3MPT are -290, -297, -325 and -284 mV versus Ag/Ag+, respectively. The redox half potentials of PBEDOT-TOL, PBEDOT-BOB and PBEDOT-FB are -130, -147 and -327 mV vs. Ag/Ag+, respectively, and a bit higher than that of PBEDOT-Ts. Moreover, the large potential plateau indicates that PBEDOT-Ts and PBEDOT-Bs are stable over a broad potential window.;All polymers exhibit electrochromism and a spectrum of colors in the undoped state, ranging from deep-purple for PBEDOT-3BT and PBEDOT-3OT to reddish for PBEDOT-FB, and blue in the doped state. In addition, these polymers show photoluminescence behavior and their PL are in the orange and red regions.;IR spectroscopy showed that the polymerization should take place at the alpha-position of the EDOT ring, with no opening of the central ring. UV-vis-NIR spectra showed the characteristic of free carrier tail for all polymers in the doped state, and one broad peak in the undoped state that is assigned to the pi-pi* transition. The optical bandgaps, obtained from the onset of the pi-pi* transition in the undoped state of these polymers range from 1.65 to 1.85 eV with moderate dc conductivities ranging from 15 to 30 S/cm in the doped state.;PBEDOT-Ts tend to be stable in the intermediate form while PBEDOT-Bs are stable in both the doped and undoped states. The stability, moderate conductivity, luminescence properties, as well as electrochromic behavior of these polymers make them good candidates for optoelectronic materials.