Poly(thieno[3,4-b]thiophene): A p- and n-Dopable Polythiophene Exhibiting High Optical Transparency in the Semiconducting State

Herein we report the synthesis and electrochemical characterization of poly(thieno[3,4-b]thiophene), a new low band gap conducting polymer with a high redox switching stability that exhibits high optical transparency in the semiconductive state. The monomer, thieno[3,4-b]thiophene (T34bT), has a low oxidation potential for polymerization, 1.02 V vs Ag/Ag+ (1.25 V vs SCE), a potential between that for the oxidation of 3,4-ethylenedioxythiopene and pyrrole. Poly(T34bT) has a band gap of ca. 0.85 eV (1459 nm) as determined by the onset for the π-to-π* transition from the UV−vis−NIR spectrum and 0.8 V from the difference in the onsets for both the p- and n-doping processes from cyclic voltammetry. Stability studies as determined from chronocoulometry and chronoabsorptometry indicate that the polymer retains 95% electroactivity and 96% change in optical density after 100 double potential steps. Poly(T34bT) is sky-blue in the reduced form and optically transparent (no observable color) in the oxidized state wit...