Design,Synthesis And Photoelectric Properties Of Hindered Group Modified Phthalazine Tris-Cyclometalated Iridium Complexes

Iridium(?)complexes are widely used in the preparation of OLED devices due to their short phosphorescent lifetime,high luminous efficiency,and facile color tenability.However,phosphorescent materials are very sensitive to concentration,and the luminescent wavelength and efficiency vary greatly with concentration changes.Therefore,it is very important and urgent to develop luminescent molecules that are not sensitive to concentration.In this paper,in order to obtain highly-efficient pure red iridium(?)complexes,triptycene structure and alkylcarbazole groups are introduced into phthalazine ligands to increase steric hindrance.Therefore,aggregation of complexes molecules is effectively avoided,and non-radiative transition rate of excited states is reduced,which is beneficial to improve the efficiency of iridium(?)complexes.This paper is divided into two parts,as follows:(1)Four tris-cyclometalated iridium(?)complexes were synthesized by using a phthalazine-based compound modified with triptycene,and the yields were between 11 %-50 %.The correctness of the synthesized products is verified by NMR and mass spectra.The single crystal structures of some of the complexes show a facial-configuration of complexes,which is consistent with the NMR results.The photophysical properties of the complexes were characterized by ultraviolet absorption spectra,photoluminescence spectra and cyclic voltammetry.The oxidation half-wave potentials of the complexes are between 0.51 V-0.59 V,and the maximum emission wavelengths of these orange-red complexes in dichloromethane solution are between 595 nm-607 nm.Compared with Ir(mdtp)3,the electron withdrawing effect of the para-trifluoromethyl to the iridium(?)atom in the complex Ir(odtp)3 is weaker than that of the meta-position,thus the HOMO energy level of the complex Ir(odtp)3 is pushed up.The conjugation extent of diphenylamine and phthalazine ring in the complex Ir(dptp)3 is less than trifluoromethylbenzene of Ir(mdtp)3,so that the HOMO and LUMO energy levels are all pushed up.The electron-donating alkyl group in the complex Ir(mdtp)3 pushes up the LUMO energy level,and the HOMO energy does not change much.By doping the four complexes in PMMA films,the lifetime and quantum yields of them are tested,which are between 1.1 ms-2.1 ms and 63.7 %-78.9 %.Among them,Ir(mhtp)3 exhibted the highest quantum yields of 78.9 %.Pure solid powder of these complexes in the air still maintains a high quantum yields between 4.5 %-11.4 %.Among them,the quantum yield of Ir(mhtp)3 is as high as 11.4 %.Both of these results indicate that the additional alkyl steric hindrance on the triptycene structure can effectively reduce the intermolecular accumulation and reduce its sensitivity to concentration.The thermal stability of these complexes is better,and the temperature at a weight loss of 5wt % is between 270 ?-450 ?.Among them,the thermal weight loss temperature of the alkyl triptycene-based complex Ir(mhtp)3 is 270 ?,the ferior thermal stability is caused by the strong electron donating of the alkyl group,but the sharp decomposition temperature of 430 ? indicates that is is still sufficient stability.Generally speaking,the triptycene-based iridium(?)complex has excellent stability and is suitable for the preparation of electroluminescent devices by vacuum evaporation methods.(2)Two tris-cyclometalated iridium(?)complexes are synthesized by a one-step synthesis method with phthalazine compounds decorated with tert-butylcarbazole groups as ligands.The yields are 12.5 % and 16 %,respectively.The correctness of the synthesized products is verified by NMR and mass spectra.The complexes are characterized by photophysical properties by ultraviolet absorption spectra,photoluminescence spectra,and cyclic voltammetry.The oxidation half-wave potentials of the complexes are 0.51 V and 0.88 V,respectively.The maximum emission wavelengths of the pure red complexes Ir(md-t Cz)3 and Ir(dp-t Cz)3 in dichloromethane solution are 628 nm and 629 nm,respectively.The emmision peak of complex Ir(dp-t Cz)3 red shifted by 1nm compared with Ir(md-t Cz)3,and the change is very small.It needs to be verified by theoretical calculation.In the PMMA films,their quantum yields are 71.6 % and 54.9 %,and the lifetimes are 1.4 ms and 1.7 ms,respectively.Their quantum yields in pure solid powders are 15.0 % and 7.2 %,respectively.The order of quantum yields is the same as that in the PMMA film,indicating that the influencing factors are the same,which are all caused by the different structures of the complexes.The thermal decomposition temperatures of the complexes Ir(md-t Cz)3 and Ir(dp-t Cz)3 are 425 °C and 410 °C,respectively.In short,the rigid steric hindrance group of tert-butylcarbazole is beneficial to reducing the sensibility to the concentration quenching of these complexes,and they have better thermal stability and shorter lifetimes,showing that they are high-efficiency pure red iridium complexes.