Synthesis And Charaterization Of Halogen-Bearing Conjugated Polymers

In this dissertation, straight-forward synthitic rout has been developed to introduce chlorine atoms onto the backbone of conjugated polymers and these chlorine-bearing conjugated polymers can be used as light-emitting materials. Additionally, bromine atoms were attached at the end of the side-chain of conjugated polymers. The effects of bromine on the conjugated polymers have been well studied. The detailed results were briefly described as below:5,8-dibromo-6,7-dichloro-2,3-bis(3-(octyloxy)phenyl)quinoxaline was designed and synthesized. Copolymerizing with2,5-bistrimethyltinthiophen, regeoregular chlorine-bearing donor-acceptor alternating conjugated copolymer (PC1QT) was obtained for the first time by taking advantage of the different reactivies between chlorine and bromine in Still reaction. The fluoride (PFQT) and non-substitued (PQT) analogues were also synthesized to systemtically study the effects of chlorine atoms on the conjugated polymers. PC1QT exhibited deepest LUMO energy level although the electron affinity of chlorine is less than that of fluorine. The calculation based on density functional theory (DFT) proved that the chlorine atoms twisted the backbone of the copolymers causing localized LUMO and resulting deepest LUMO energy level. When2,2’-bithiophene was used as the donor moiety, the resulted copolymer PC1Q2T exhibited higher HOMO compared with that of PC1QT and maintained deep LUMO energy level indicating the HOMO and LUMO levels can be modified individually. These chlorine-bearing copolymers exhibited blue-shifted absorption spectra and large Stokes shift which can be attributed to the large steric hindrance of chlorine atoms.5,8-dibromo-6,7-dichloro-2,3-bis(3-(octyloxy)phenyl)quinoxaline was used as the acceptor moiety and oligomer thiophenes were used as the donor moieties, three red-emitting copolymers, PClQ2HT、PClQ3T and PClQ4T, were obtained by changing the number of thiophene. Efficient green-emitting F8BT was chosen as the host material to fabricate polymeric light-emitting diodes. When PClQ3T was used as the guest light emitting material, Deep red centered at678nm, CIE (0.66,0.34) with brightness about2000cd m-2and EQE above1%was obtained; When PClQ4T was used as the guest light emitting material, deep red to NIR emission centered at698nm with brightness about1500cd m-2and centered at708nm with brightness over400cd m-2with reasonable efficiency (0.21-0.69%) was obtained. All these results obtained with simple device structure ITO/PEDOT:PSS/light emitting layer/Ca/Al, indicating the chlorine-bearing copolymers are competitive deep red to NIR light-emitting materials.4,7-dibromo-5,6-dichlorobenzo[1,2,5]thiadiazole was synthesized and used as the acceptor moiety to synthesize conjugated polymers. In this molecule, the difference in reactivity between the chlorine atoms and the bromine atoms is too small to process Stille reaction but large enough to process Suzuki reaction to obtain regioregular chlorine-bearing polymers with high molecular weight. Higher LUMO levels of the final polymers were observed compared with non-chloride polymers. The calculation results based on DFT indicated different effects of chlorine atoms on polymers containing benzothiadizole and quinoxaline respectviely could be attributed to the differences in electron withdrawing ability and steric hindrance between the thiadizole of benzthiadizole and the pyrazine of quinoxaline. Efficient red-emitting polymer PFClDTBT was obtained when4,7-bis(5-bromothiophen-2-yl)-5,6-dichlorobenzo[c][1,2,5]thiadiazole was used as the acceptor moiety and fluorene was used as the donor moiety. The single-layer devices with the configuration of ITO/PEDOT:PSS/Polymer/Ca/Al exhibited saturated red emission at632nm with a luminous efficiency of1.2cd A-1with CIE (0.60,0.40) when the doping ratio was3%. The maximum brightness and external quantum efficiency (EQE) could reach15580cd m-2and1.1%respectively. A series of donor materials were obtained by finely tuning the content of bromine attached at the side-chain of conjugated polymers. Theses bromine atoms could affect the optical properties when the donor materials were dissolved in solvent, can not only change the absorption coefficiency but also make the fluorescence emission maxima red shift. When the materials were cast on quartz, the shoulder peak in absorption spectra became clearer but no change happened in the fluorescence spectra. This is because that the effect of polarized bromine atoms is weaker than the dipole-dipole interaction of segments. When the materials were dissolved, the effect of polarized bromine overwhelmed because the segments are far away from each other and caused changes in optical properties. But in, films, dipole-dipole interaction of segmetns is dominant resulting the same fluorescence spectra. Additionally, weak interaction might exist because of bromine atoms resulting clearer shoulder peak in the absorption spectra.