Synthesis and characterization of novel low band-gap polymers containing squaraine units

Novel conjugated polymers based on squaric acid having 2,5-Bis[(E)-N-alkylpyrrol-2-ylvinyl]-3-alkylthiophene (PVTVP) unit in the main chain were successfully synthesized in good yields through polycondensation reaction. Their molecular structures were characterized by FT-IR and 1H NMR. They have good solubility in common organic solvents, good thermal stability by thermal gravimetric analysis and high molecular weights. Their optical properties were investigated by UV–vis absorption spectra in CH2Cl2 solution, the results indicated all these compounds showed broad and strong spectral responses from 200 nm to 900 nm, suggesting their potential for application as organic plastic solar cells.