Six types of donor-acceptor conjugated polymers were designed by choosing thieno[3

2-b]thiophene (TT) as the electron donor and Benzo[c][1

2

5]thiadiazole (BT)

[1

2

5]thiadiazolo[3

4-g]quinoxaline (TdQ) or benzobis[1

2

5]thiadiazole (BBT) as the electron acceptor unit.B3LYP method is employed to investigate the electronic structure and properties of the designed TT-based donor-acceptor alternating copolymers.It is found that the electron-withdrawing ability of the acceptor and the ratio of donor to acceptor units (D/A ratio) play a very important role in the geometries and electronic properties for the donor-acceptor alternating copolymers.The bridge bond length and the average bond length of carbon-carbon single bond (LAS) in the donor unit decreases with an increase in the electron-withdrawing ability of the acceptor moiety.However

the average bond length of carbon-carbon double bond (LAD) in the donor unit shows a same trend as that of the acceptor strength.In addition

the bridge bond length increases with an increase in the D/A ratio for the copolymers.It is of interest to note that the electronic properties of the TT-based copolymers

especially for the copolymers with the D/A ratio of 2:1

also exhibit a systematic trend with the acceptor strength.The band gap (Eg) and effective mass of carriers (both hole and electron

mH and mL) decrease

the bandwidth (both valence and conduction band

WVB and WCB) increases systematically with an increase in the electron-withdrawing ability of the acceptor moiety.The theoretical results also suggest that p-TdQ-TT and p-BBT-DT could have potential applications as an electrically conductive material due to their narrow band gap ( 0.5 eV)

large bandwidth and small effective mass of holes and electrons.