Polydibenzothiophene: Effect of molecular weight on photoelectric performance

Abstract

Polydibenzothiophene (PDBT) was synthesized via palladium-catalyzed Suzuki coupling reaction from 2,8-dibromodibenzothiophene and 2,8-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-dibenzothiophene. Since molecular weight is an important factor determining the organic photoelectric performance, PDBT was prepared with molecular weight (Mn) varying from 6 kDa (extracted by dichloromethane, PDBT-D) to 12 kDa (extracted by chloroform, PDBT-C). Amorphous PDBT-D and PDBT-C both emitted blue photoluminescence with close PLQYs of 3.6 and 2.8 % in CHCl3, showed similar electrochemical band gap of 2.26 and 2.18 eV, presented no significant thermal transitions, and exhibited uniform homogeneous morphology. The photoelectric performance exhibited the obvious different compared with monomer DBT, observing obvious Tm and Tc as well as compact coralline surface morphology. To better understand the influence of Mn for the above organic photoelectric performance, DFT calculations were performed. We have calculated different repetitive unit of DBT, signed as (DBT)n, n means the number of repetitive unit. In this theoretical calculation, when the repetitive unit of DBT increase to 9 and 12, namely (DBT)9 and (DBT)12, the LUMO/HOMO levels and even dipole moment were not changed. Videlicet, in our model system, Mn of PDBT surpass about 1.6 kDa, its organic photoelectric properties would perform no significant change. The study provide guidance for effect research of molecular weight on photoelectric performance.