Highly efficient synthesis of thieno[3,4-b]thiophene derivatives and (opto)electrochemical properties of new low bandgap conjugated polymers

Various thieno[3,4-b]thiophene derivatives functionalized by n-octyl, 4-tert-butylphenyl, 4-n-butylphenyl, and 4-n-pentylphenyl were synthesized in a concise and efficient way. Previously reported synthetic processes were modified to produce target molecules in relatively high yields. Electrochemical and optical properties of polymers were examined by cyclic voltammetry and Vis–NIR spectrophotometry. The bandgap of electrochemically prepared polymers varied with substituents, ranging from 0.91 eV to 0.98 eV. While HOMO of conjugated polymers was raised by inductive effect of alkyl substituents, the bandgap was mainly determined by resonance stabilization of phenyl substituents.