Water Dispersible Low Band Gap Conductive Polymer Based on Thieno[3,4-b]thiophene

Herein we describe the synthesis and properties of poly(thieno[3,4-b]thiophene) (PT34bT), a new low band gap polymer that shows high optical transparency in oxidized conductive state. Thieno[3,4,b]thiophene was polymerized in water using chemical oxidants in the presence of poly(styrenesulfonic acid). Since poly(styrenesulfonic acid) is water soluble and there are strong interactions between poly(styrenesulfonate) and the oxidized PT34bT, the resulting polymer system is rendered a colloidal dispersion. PT34bT-PSS has a band gap of ca. 1.08 eV (1150 nm) depending on oxidants used as determined by the onset of the π to π* from the Vis-NIR spectrum with a peak at an energy of 1.63 eV (760 nm). Diluted PT34bT-PSS dispersions are transmissive green in the oxidized form and become transmissive blue in reduced state. Electrical conductivities for these polymers are dependent on chemical oxidants used and are varied from 0.01 to 10−4 S/cm.