A novel polymer PTST bearing substituted squaric acid units in the main chain is synthesized via Yamamoto coupling reaction in the presence of Ni(PPh3)2Cl2 as catalyst

and the chemical structure of PTST is confirmed by1H-NMR

13C-NMR and FTIR.The polymer PTST is readily soluble in common organic solvents such as chloroform

tetrahydrofuran

methylene dichloride

chlorobenzene and 1

2-dichlorobenzene

thus uniform thin films can be prepared from these solutions.The result from TGA shows that the polymer has excellent thermostability.The UV-Vis absorption spectrum of the polymer in tetrahydrofuran shows broad and strong absorption bands in the range of 270~700 nm and low band gap

suggesting that the polymer has good coverage with the solar spectrum.The result of cyclic voltammetry indicates that the lowest unoccupied molecular orbital (LUMO

-3.77 eV) and band gap (Eg) of the polymer are decreased by incorporation of the 3-cyclobutene-1

2-dione segment

implying that the polymer is nearly similar to that of perylene diimide-based polymers (-3.9 eV)

indicating that the polymer PTST is a potential n-type polymer material for fabrication of polymer solar cells.When blend poly(3-hexylthiophene) (P3HT) with the polymer PTST

even under a low doping ratio of 20 wt%

P3HT would lead to the PL quenching of P3HT obviously

while higher doping ratio of 1∶1 (W∶W) would lead to completely quenching of emission from P3HT

suggesting that there exists efficient photoinduced electron transfer from P3HT to the target macromolecule.All these photophysical and electrochemical properties indicate that the objective copolymer PTST is a potential polymer acceptor material.