Synthesis And Properties Of Organic Crosslinkable Luminescent Materials

In recent years,OLED has become a research hotspot and is gradually moving towards commercialization.According to the difference of the light-emitting principle of materials,the luminescent materials can be divided into fluorescent and phosphorescent materials.Phosphorescent materials are more arresting because of its higher internal quantum efficiency.Iridium???complexes are one of the most widely studied phosphorescent materials.Phosphorescent materials have TTA?triplet-triplet annihilation?and concentration quenching effects when prepared devices,so they usually appeared in the form of doped devices.The solution spin-coating method is widely used because it has many advantages,such as saving materials,simple operation and low cost.However,this method also has the main disadvantage of intermixing and corroding.Therefore,how to get low cost and good performance devices is worth exploring.The use of cross-linking materials can effectively improve this phenomenon.The small organic light-emitting materials grafted the functional groups?oxetane or vinylbenzyl?can be photo-crosslinked or heat-crosslinked into the polymeric organic light-emitting materials.When the OLED device is preparing,the crosslinkable light-emitting material and the host material?with the same crosslinkable functional groups?undergo a polymerization reaction through external conditions.The entire emitting layer will be changed from independent small molecules to a macromolecule film by chemical reactions.The film has solvent resistance,which can effectively avoid the problem of inter-layer miscibility.This thesis mainly focused on synthesis of a variety of first ligands or second ligands with cross-linking groups,and further synthesized new cross-linkable neutral iridium???complexes,and measured a series of properties of the complexes.The main work is divided into the following three parts:In the first part,2-phenylpyridine was used as the first ligand of the complex,which is the classic ligand for green iridium???complex,and then the different ligands with two different cross-linking groups?oxetane or vinylbenzyl?were used as the second ligands.Further,three single crosslinkable neutral iridium???complexes were synthesized,in which the second ligands of the complexes were cross-linking acetylacetone?acac?and3-hydroxypicolinic acid,respectively.The three complexes were named as Ir?ppy?₂?acac-oxe??Ir-1?,Ir?ppy?₂?acac-VB??Ir-2?and Ir?ppy?₂?pic-VB??Ir-3?.They have the typical emission type of the Ir???complexes,and the main emission peaks are located at 529,521 and 531nm.The maximum photoluminescence quantum yields of the complexes in the solution are1.77%,0.42%and 1.77%,respectively.Their thermal decomposition temperatures are 268,207 and 330?,respectively.The devices of complexes Ir-1 were prepared by solution spin-coating method,and the device structure is ITO/PEDOT/PVK:PBD:Ir?x wt%??40nm?/TPBi?40 nm?/Liq?2.5 nm?/Al?120 nm?.The results show that the maximum luminance of the complexe is 2494 cd/m²,the maximum current efficiency is 6.91 cd/A and the maximum external quantum efficiency?EQE?is 1.88%.The second part has made some changes in the thinking of the first part.Considering that increasing the number of cross-linking groups can increase the probability of cross-linking to form a good film.Therefore,the modification position of the cross-linking group is transferred from the second ligand to the first ligand,that is,the main body of the first ligand is 2-phenylpyridine,and the cross-linking groups are modified on it.Two neutral Ir???complexes with two cross-linkable groups were synthesized by using acetylacetone and Stpip as the second ligand.Two complexes were named as Ir?ppy-VB?₂?acac??Ir-4?and Ir?ppy-VB?₂?Stpip??Ir-5?.The main emission peaks of them are located at 519 and 516 nm.The maximum photoluminescence quantum yields of the complexes in the solution are 2.71%and 0.39%,respectively.Of the two complexes,the complex Ir-4 has more excellent photophysical properties.Their thermal decomposition temperatures are 330 and 228?,respectively.The third part is consistent with the second part.Only the main part of the first ligand was replaced by 2-phenylbenzimidazole,which is also widely used in green Ir???complexes.Two Ir???complexes with two cross-linkable groups were synthesized,which were named as Ir?pbm-VB?₂?acac??Ir-6?and Ir?pbm-VB?₂?Stpip??Ir-7?.The main emission peaks of them are located at 513 and 504 nm.The maximum photoluminescence quantum yields of the complexes in the solution are 2.21%and 0.36%,respectively.Their thermal decomposition temperatures are 233 and 394?,respectively.