Synthesis And Properties Of Organic Electron Transport Materials Based On Imidazo [1,2-a] Pyridine

Organic semiconductor materials have attracted great interests of many research groups because of their wide application.For applications such as displays and solid-state lighting,organic light-emitting diode(OLED)has emerged as an emerging alternative to traditional light sources due to its high contrast,low power consumption and flexibility.OLED mainly consists of an emitting layer,a charge injection layer and a transport layer between two electrodes.The efficiency and lifetime of devices are strongly dependent on the balance of electrons and holes injected from the electrode and transported to the EML.It is very important to control the charge injection balance of EML emitting materials.In order to maximize the device performance of red,green and blue light simultaneously,it is necessary not only to study various EML materials,but also to develop new charge transfer materials.However,in the past few decades,researchers mainly focused on luminescent materials and hole transport materials(HTM),electron transport materials(ETM)have not much progress.Ideal electron transport materials generally need to have high thermal stability,deep LUMO/HOMO,high triplet state,high electron mobility and other characteristics.At present,the number and type of electronic transmission materials are less,and the function is single,the application of device driving voltage is high,low efficiency,poor stability and other problems.To solve these problems,we studied new imidazo[1,2-a]pyridine groups,searched for better substitution sites for the design of electron transport materials,and designed and synthesized SF-Dp1 of imidazo[1,2-a]pyridine linear phenyl para-linked spirodifluorene,SF-Dp2 of side-chain phenyl para-linked and SF-DP3 of side-chain phenyl para-linked.Imidazolo[1,2-a]pyridyl para-phenyl connections have higher electron mobility,SF-Dp1 and SF-DP3 devices can effectively reduce the driving voltage than SF-Dp2 devices,SF-Dp1 due to the deep LUMO(-2.85 e V),green phosphorescent device brightness attenuation to 97%of the longest life.Up to 126 h,the SF-DP3 has a higher triplet state(2.75 e V)and a longer life of about 16 h when applied to blue devices with luminance attenuation up to 97%.Especially for green phosphorescent devices,the CE of SF-Dp1 and SF-Dp3 are 52.0 and 52.1 lm/W,respectively,about 17%higher than that of SF-Dp2 devices.Based on the high electron mobility and deep LUMO of SF-Dp1 linked by imidazo[1,2-a]pyridine group,TRZ-PA-DP and TRZ-PP-DP with higher electron mobility were designed.Imidazo[1,2-a]pyridine fragment contained imidazo and pyridine unit,which was a strong electron-absorbing fragment.TRZ-PA-Dp and TRZ-PP-DP have high thermal stability and glass transition temperatures up to 172 and 146?,respectively,which can form stable amorphous films during the preparation of the device.TRZ-PA-Dp and TRZ-PP-Dp have deeper LUMO(-2.84 e V),and their electron transport mobility is higher than that of TPBi.Moreover,the deep HOMO also has the function of hole blocking.When applied to green phosphorescent devices,the driving voltage of TRZ-PA-Dp and TRZ-PP-Dp devices is 2.6 V at 100 cd/m~2,0.6 V lower than that of TPBi device,the external quantum efficiency(EQE)is 17.4%and 17.5%,and the current efficiency(CE)is 63.1 and 63.5 cd/A,respectively.EQE and CE both improved by about 5%,and power efficiency(PE)was 76.6and 76.7 lm/W improved by about 28%,respectively.The device life is up to 390 h,about 5times that of TPBi device.