电子受体强度对基于Thieno[3,2-b]thiophene的共轭聚合物电子性质的影响

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

摘要:

采用杂化的密度泛函方法(DFT/B3LYP)，在6-31G(d)理论水平下研究了基于噻吩并[3,2-b]噻吩（Thieno[3,2-b]thiophene，TT)）的D-A型共轭聚合物的几何结构、电子结构和性质. 研究发现，在以TT为电子供体的D-A型共轭聚合物中，电子受体强度是影响其几何结构、电子结构和性质的重要因素. 对基于TT的电子受体与电子供体交替排列的D-A型共轭聚合物，在一定范围内，电子受体强度增加，有利于减小共轭聚合物的键长交替，降低聚合物的能隙，并使其能带变宽，电子离域程度增大，载流子有效质量减小，载流子迁移能力增强. 但受体强度过大，键长交替反而增大，能带和能隙均变窄，载流子迁移能力减弱.

Abstract:

The donor-acceptor(D-A) conjugated copolymer were designed by choosing Thieno[3,2-b]thiophene(TT) as the electron donor and quinoxaline(Q), Benzo[c][1,2,5]thiadiazole(BT), pyrazino[2,3-g]quinoxaline(PQ), [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ) or Benzobis[1,2,5]thiadiazole (BBT) as the electron acceptor unit. The DFT/B3LYP method is employed to investigate the electronic structures and properties of the donor-acceptor alternating copolymers. The theoretical results suggest that electron-acceptor strength contribute significantly to the geometrical structures and electronic properties of the alternating donor-acceptor copolymers. The geometrical and electronic properties of the TT-based copolymers exhibit a systematic trend with the electron-acceptor strength within a certain range. The bond length alternation, band gap (Eg) and hole effective mass decrease, the bandwidth (both valence and conduction band) increases systematically with an increase in the electron-withdrawing ability of the acceptor moiety within a certain range of the electron-acceptor strength.