Thin films of poly 3, 3’ dibromo, 2,2’ biththiophene (PDBrBTh) and poly 2,2’ biththiophene (PBTh) on fluorine doped tin oxide electrode (FTO) were subjected to optical, electrochemical and impedance studies in various aqueous electrolytes. Both polymers showed electrochromic properties, where the neutral film at -1.0 V vs Ag/AgCl shows red color, and the oxidized (doped) film at positive potentials shows blue color. Optical studies indicated that PDBrBTh showed a greater optical band gap than that of PBTh. Our studies also showed that the presence of bromine as a substituent at the C-3 position of the thiophene ring causes a greater ionization potential (IP) than PBTh. PDBrBTh also shows closer values of refractive index(n), and real (εr,) and imaginary (εi) dielectric constants to that of PBTh at photon energies between 2.0eV and 3.0 eV. At lower photon energy PDBrBTh showed lower optical conductivity than Br-free PBTh. Study also indicated that PDBrBTh is much less photoactive that PBTh. Electrochemical impedance spectroscopic studies (EIS) revealed that PDBrBTh possesses less relaxation time, and less double layer capacitance (Cdl) in dark and under illumination.

Particles of TiO 2 modified with poly 3-(2-thienyl) aniline (PThA) and occluded in poly 2,2 bithiophene (PBTh), were subjected to optical, electrochemical impedance spectroscopic (EIS) and photoelectrochemical (PEC) investigation in aqueous, acetate, citrate, and phosphate electrolytes. EIS studies revealed that the assembly film of TiO 2 /PThA/PBTh possess porous-type structure. They also confirmed the approximate value of E f obtained from electrochemical studies. Both EIS and optical studies indicated that ac conductivity is much greater than dc conductivity. Guided by the properties of PBTh, no large changes in the energy band structure occurred due to occlusion of TiO 2 in PBTh films. Occlusion of TiO 2 /PThA into the network structure of PBTh inhibits the energy dissipation process and impeded charge polarization process of the material. Photoelectrochemical outcome suggested possible band alignments between the organic film and TiO 2 and formation of hybrid sub-bands. Inclusion of TiO 2 in the thiophene-based polymers enhanced the charge separation and consequently charge transfer processes and widen the absorption in visible light range.