Synthesis and Property Study of Field-effect Emissive Conjugated Polymers Based on Styrene and Benzothiadiazole

Conjugated polymer materials with good photoelectric performance, solution processing ability and flexibility are widely used as active layers in optoelectronic devices. Here, using Stille and Suzuki coupling reactions, we designed and synthesized two new conjugated polymers, poly(1,2-bis(2,5-bis(iso-octyloxy)phenyleneviny lene-2,1,3-benzothiadiazole)) (PVBT) and poly(1,2-bis(2,5-bis(n-octyloxy)phenylenevinylene-2,1,3-benzothiadiazole)) (nPVBT), which contain structural element styrene fragments and an conjugated unit benzothiadiazole. Styrene fragments are conducive to luminescent properties of materials, such as phenylenevinylene (PPV) derivatives, while benzothiadiazole unit is electron withdrawing, and matches with many structural units of a donor. The conjugated polymers were characterized by gel permeation chromatography (GPC), elemental analysis and differential scanning calorimetry (DSC). The results indicate that each of these two polymers has good thermal stability. Their melting points were around 240 similar to 250 degrees C and decomposition temperatures around 380.. Due to the presence of the structural alkoxy chains, these two polymers exhibit good solubility, which is conducive to solution-processed film formation. PVBT and nPVBT have strong fluorescence characters with maximum emission in the range of 590 similar to 605 nm. The photoluminescence quantum yield of these two polymers in dichloromethane solution (1x10(-5) mol.L-1) is 23%similar to 35%, and 12%similar to 20% in solid films, which are annealed at 180 degrees C for 10 min. Due to benzothiadiazole's regulation of molecular energy levels, the highest occupied molecular orbital (HOMO) energy level of PVBT and nPVBT were modulated to be -5.73 and -5.61 eV, and the lowest unoccupied molecular orbital (LUMO) energy level were -3.37 and -3.32 eV, respectively. Typical p-type transporting property was determined by using PVBT and nPVBT films as active layers in organic field effect transistors. Because of the improved conjugation of the skeleton structures and the close packing between benzothiadiazole of main chains, these two conjugated polymers both exhibit efficient charge transport characteristics with saturation hole carrier mobility is up to 1.1x10(-4) cm(2).V-1.s(-1) and high switching on/off ratio of 10(3)similar to 10(4). This work provides new insight into the development of high-performance optoelectronic conjugated polymer materials and sheds light on the research of organic optoelectronic integrated devices.