供体-受体型共轭聚合物电子结构和导电性能的理论设计

以苯并1,2-c:4,5-c']二1,2,5]噻重氮和吡嗪并2,3-g]喹喔啉为电子受体(A),噻吩、噻吩并3,2-b]噻吩和二噻吩并2,3-b:2',3'-d]噻吩为电子供体(D),设计了6种D-A型共轭聚合物.采用B3LYP方法,研究了这6种聚合物的几何结构和电子性质.D-A型共轭聚合物的几何结构和电子结构与电子供体和电子受体的性质,特别是与其提供电子和接受电子的能力密切相关.聚合物的能隙主要受键长交替控制,键长交替越小,能隙越窄.所设计的6种聚合物中,p-BBT-TT具有较窄的能隙(0.48 eV)、较小的载流子有效质量和相对较大的能带宽度,具备理论上的良好导电性能,可能是潜在的优良导电聚合物材料.

THEORETICAL DESIGN OF THE ELECTRONIC STRUCTURES AND CONDUCTION PROPERTIES OF CONJUGATED DONOR-ACCEPTOR COPOLYMERS

Six conjugated donor-acceptor copolymers were designed by choosing benzo1,2-c:4,5-c′]bis -thiadiazole or thiadiazoloquinoxaline as the acceptor and thiophene,thienothiophene or dithieno2,3-b:2′,3′-d]thiophene as the donor unit.The electronic structure and properties of the designed copolymers were investigated systematically using the hybrid density functional theory method.The properties of the donor and acceptor moieties,especially the properties of the electron-donating and the electron-accepting ability,play a very important role in the geometric and electronic structures for the D-A copolymers.The theoretical study shows that the bridge bond length decreases regularly with an increase in the electron-accepting ability of electron acceptor,and increases regularly with an increase in the electron-donating ability of electron donor.In addition,the intramolecular charge transfer between the donor and acceptor moieties increases with an increase in the electron-accepting ability of acceptor and the electron-donating ability of donor.It is found that the band gap of the D-A copolymers is mainly controlled by the bond-length alternation along the main chain.The energy gap decreases with decreasing bond-length alternation.Namely,the band gap is decreased systematically with the decrease of bond-length alternation in the main chain.Among the designed copolymers,polymer p-BBT-TT is a very good candidate for an electrically conductive material due to its very small band gap(0.48 eV),large bandwidth and small effective mass of holes and electrons.