The effects of electron-acceptor strength and donor-to-acceptor ratio on the electronic properties of thieno[3,2-b]thiophene-based donor-acceptor copolymers

摘要

Theoretical analysis on the geometries and electronic properties of thieno[3,2-b]thiophene (TT)-based alternating donor- acceptor conjugated polymers of donor and acceptor unit with the ratio of 1:1 and 2:1, as well as their corresponding monomers, is reported. The theoretical results suggest that both the electron-acceptor strength and the mole ratio of donor to acceptor (D/A ratio) contribute significantly to the electronic properties of alternating donor-acceptor conjugated copolymers. However, the impact of D/A ratio on the geometrical and electronic properties of the donor-acceptor copolymers is more marked compared with that of the acceptor strength. The increase in the portion of TT unit can significantly decrease the bond length alternation, strengthen the π-electron delocalisation and narrow the band gap. In addition, the mole ratio of donor-to-acceptor unit also has an impact on the bandwidth. The copolymers possessing a D/A ratio of 2:1, i.e. p-TTP-DTT, p-DTP-DTT and p-TBT-DTT, may be good candidates for conduction materials due to their very narrow band gap (<0.72 eV), relatively small effective mass of carriers and relatively large bandwidth.