Electrochemical and optical properties of 3',4'-bis(alkyloxy)-2,2':5',2"-terthiophene bearing multifunctional polymers: Effect of alkyl chain length on electrochromic properties

Herein, three multifunctional 3',4'-bis(alkyloxy)-2,2':5',2"-terthiophene comprising monomers with different alkyl chains were electrochemically polymerized on an ITO electrode to obtain the polymers; poly(3',4'-dibutoxy-2,2':5',2"-terthiophene) (P1), poly(3',4'-bis(hexyloxy)-2,2':5',2"-terthiophene) (P2), and poly(3',4'-bis(octyloxy)-2,2':5',2"-terthiophene) (P3). Cyclic voltammetry and in situ spectroelectrochemical studies were performed for the polymers to investigate their oxidation potentials, HOMO/LUMO energy levels, band gaps (Eg(op)), optical contrasts (T%), and switching times. All polymers had an optical band gap at around 1.8 and 1.9 eV and revealed different tones of red color in their neutral states and different tones of blue color in their oxidized states with similar electrochromic features. This means that the alteration of the alkyl chain lengths did not affect the band gap and the colors of the resulting polymers significantly. When P1, P2, and P3 were compared in terms of electrochromic contrast and switching studies, P1 had superior optical contrast and switching time values. P1 exhibited 51% optical contrast at 520 nm which is a rare and desired property for p-conjugated conducting polymers in the visible region. P1, P2 and P3 conducting polymer films, which were also used for energy storage applications before, revealed promising electrochromic characters in this study, so these poly(3',4'-bis(alkyloxy)-2,2':5',2"-terthiophene) derivatives can be called as multifunctional next-generation materials.