Preparation Of4-Substituted Phthalazinones From Bis-Weinreb Amides And Their Application In Electrophosphorescent Materials

4-Substituted phthalazine,plays an important role in the application of medicine and material industry,of which an efficient synthesis method has not reported yet.In this work,we have developed an efficient as well as simple two-step method firstly for synthesizing4-substituted phthalazine based on the reaction of bis-Weinreb amides and Grignard reagent,which was then successfully applied in synthesizing iridium phosphorescent complexes.1.Research on the reaction of bis-Weinreb amidewith Grignard reagent and its applicationAt room temperature,with dry THF as the solvent,N1,N2-dimethoxy-N1,N2-dimethyl-phthalamide reacted with 4 equivalent ratio of Grignard reagent and completely converted into ring-opening or lactone monoamide.With a high chemoselectivity,the reaction yield was between 25%and 89%.Amide substrates reacted with a variety of Grignard reagents containing alkyl,aryl or heterocyclic group.The reaction was significant influenced by the distance of two amide groups and remarkably influenced by the electronic and steric effect of metal reagent,but affected slightly by the group of Weinreb amide substrate.In addition,we speculated that intramolecular nucleophilic reaction occurred during the reaction process based on the formation of lactone structure.At same time,a stable intermediate must produce to ensure that only monoamide products are generated.By condensation with hydrazine hydrate,4-substituted phthalazine was prepared with the monoamide product in high yield（40～88%）successfully.With much convenient operation than other ways,the two-step method can be used to prepare4-substituted phthalazine in high purity for it can be precipitated directly from the solution after reaction.In a word,the new reaction has mild conditions,convenient operation and wide applicability of substrates,especially efficient and convenient during the preparation of4-substituted phthalazine.2.Research on photoelectric properties of phosphorescent iridium complexesIn order to reduce the concentration quenching of iridium complexes and improve their current carrying transport performance,rigid cycloalkyl steric hindrance groups were introduced into the synthesizing of phthalazine tricyclic metal iridium complexes,resulting in two symmetrical iridium complexes Ir1 and Ir2.At the same time,using the above new synthesis method,diphenylamine hole transport unit was also introduced and two symmetrical iridium complexes Ir3 and Ir4 were prepared.1.The thermal decomposition temperature of four complexes ranges from 390℃to 436℃,showing good thermal stability.Their emission wavelength is between 614 nm and 629 nm in solution and the luminescence lifetime ranges from 1.04μs to 2.65μs.The photoluminescence quantum efficiency of PMMA films based on Ir1～Ir4 ranges from 43.7%to 70.7%.With a70.7%of quantum efficiency,Ir1 shows the best luminescence performance among these complexes and Ir2 followed by 67.4%.The photoluminescence quantum efficiency of Ir1～Ir4powder sample is between 5.8%and 15.2%,which is lower than that of thin films but still remains a high level compared with other iridium complexes without steric groups.2.The EL wavelength of doped devices（10%）D1～D4 ranges from 616 nm to 640 nm and their maximum EQE is between 5.1%and 24.4%.With a 616 nm of EL wavelength,D1 shows a red light emission and its CIE coordinate is（0.65,0.35）,which is close to that of the standard red light.The maximum brightness of D1 is 11920 cd m^-2,the maximum current efficiency is 25 cd A^-1,and the maximum EQE is as high as 24.2%,representing the highest level of EQE in phthalazine red OLEDs reported yet.In addition,D1 has a minimum efficiency roll off of 25.2%at the brigtness of 1000 cd m^-2among these devices.Through the modification of ligand,the concentration quenching of luminescence molecules significantly reduced and the performance of devices based on these complexes remarkably improved.These complexes showed great application potential in the field of OLED.Generally,the molecular design strategy was proved to be effective to improve the properties of luminescent materials.