Vapor Phase Polymerization of Thieno[3,4-b]thiophene-Tosylate and Its Application for Dynamic Structural Coloration

Reversible redox switching of conducting polymers modulates their electrochemical and electronic properties, such as polymer conformation, doping level, conductivity, and color. In turn, such electrochemical tuning are beneficial attributes to be applied for energy storage devices, displays, sensors, and much more. For certain conducting polymers, vapor phase polymerization (VPP) has shown particularly useful to form highly conductive and solvent free smooth homogenous thin films on any substrate. Herein, we demonstrate for the first time VPP deposition of the conducting polymer thieno[3,4-b]thiophene-Tosylate (pT34bT-Tos), leading to record high electrical conductivity of around 700 S cm⁻¹ at room temperature for this polymer. As observed high electrical conductivity could be achieved by systematic optimization of deposition conditions such as polymerization time, temperature, and oxidant concentration. Extinction spectra of resulting pT34bT:Tos thin films shows metallic absorption in their oxidized state, manifested as a wide near-IR absorption band extending beyond 2000 nm. We further show that the pT34bT thin films can be used for electrochemical switching as well as UV-patterned structural coloration applications. Electrochemical reduction reveals a neutral low bandgap peak around 1000 nm, making the pT34bT comparably transparent also in its neutral state compared to common conducting polymers. We further show that the VPP process is compatible with UV patterning to spatially control polymer conductivity and thickness, as used to create structurally colored images using the polymer as cavity spacer layer. Finally, we demonstrate dynamic electrochemical tuning of the structural colors by the application of different electrochemical potentials.