Poly(thieno[3,4-b]thiophene)-poly(styrene sulfonate): a low band gap, water dispersible conjugated polymer

Herein we report the oxidative chemical polymerization of thieno[3,4-b]thiophene (T34bT) using several different oxidants including ferric sulfate, ammonium persulfate, and hydrogen peroxide in the presence of poly(styrenesulfonic acid) in water and properties of the resulting poly(thieno[3,4-b]thiophene)-poly(styrenesulfonic acid) (PT34bT-PSS) dispersion. The PT34bT-PSS is rendered a colloidal dispersion in water with a particle size diameter ranging between 180 and 220 nm depending on the oxidant used for polymerization. PT34bT-PSS films have band gaps of ca. 1 eV (1260 nm) as determined by the onset of the pi to pi transition from the vis-NIR spectrum with absorption maxima ranging from 1.4 eV (912 nm) to 1.7 eV (724 nm). The neutral and oxidized forms of PT34bT-PSS prepared from ferric sulfate dispersed in water were blue and lime green, respectively, whereas the neutral and oxidized forms of PT34bT-PSS prepared from ammonium persulfate and hydrogen peroxide were blue and blue-green, respectively. Spectral properties of the PT34bT-PSS dispersion can be tuned by the combination of oxidants. PT34bT-PSS films showed ca. 100% cation dominant ion transport behavior as determined by electrochemical gravimetry with each charge-discharge cycle and the doping level of the polymer was calculated to be 26%. Electrical conductivities for these polymers were found to be dependent on chemical oxidants used and varied from 10(-2) to 10(-4) S/cm.