Design And Synthesis Of Phenanthroimidazole-based Deep-blue Fluorescent Functional Materials And Their Electroluminescent Devices

Organic Light Emitting Devices(OLEDs)are attracting more attention from researchers and businessmen as a new generation for solid-state lighting and full-color displays.In phosphorescent devices,it is possible to utilize singlet-and triplet-state excitons with up to 100%external quantum efficiency.So far,red and green OLEDs have reached commercial applications,while blue-phosphorescent devices have short lifetimes and serious efficiency roll-off problems.Blue fluorescent materials are superior to blue phosphorescent materials in terms of lifetime and device stability.Using blue fluorescent material instead of blue phosphorescent material,can achieve efficient and stable white light,reduce energy consumption,and can be also used as the host material.Therefore,the development of efficient and multi-functional deep blue fluorescent materials is crucial for the industrialization of OLEDs.Based on phenanthroimidazole as building block,a series of deep blue phenanthroimidazole derivatives were designed and synthesized by modifying the N-1position of imidazole in this paper.Their thermodynamic,photophysical,and electrochemical properties were investigated in detail and the relationship between structure and property was studied.Highly efficient deep blue non-doped fluorescent/phosphorescent devices were obtained.AD-BPI is synthesized by bridging bis-phenanthroimidazole with adamantane at the N-1 position of imidazole.The introduction of adamantane effectively inhibits intermolecular packing and increases the glass transition temperature of the molecules themselves,thereby enhancing the film-forming properties of the device preparation process.Single-carrier devices show excellent bipolar-transporting properties.The non-doped deep blue OLEDs based on AD-BPI shows the maximum brightness of 12703cd m^-2,and the maximum efficiency of 4.4 cd A^-1,3.91 lm W^-1,and 5.8%,respectively,and CIE coordinate of(0.15,0.07).In addition,green,yellow and red phosphorescent OLEDs based on AD-BPI as host display outstanding performance with the peak value of23.3%?16.7%and 19.1%with little efficiency roll-off.Two near-ultraviolet luminescent materials FL-PI and FL-BPI were designed and synthesized by introduction of 9,9-diphenylfluorene into phenanthroimidazole via the N-1position of imidazole.Both FL-PI and FL-BP display good thermal stability and high PLQY and sufficiently high E_T.The non-doped OLEDs based on FL-BPI exhibit the maximum brightness of 10252 cd m^-2,the maximum efficiency of 5.4 cd A^-1,3.8 lm W^-1,5.4%and CIE coordinate of(0.15,0.05).The green phosphorescent OLEDs based on FL-PI/FL-BPI as host demonstrate the maximum brightness of 30330 cd m-2/43620 cd m^-2,the maximum efficiency of 28.8 cd A^-1/75.3 cd A^-1,21.1 lm W^-1/27.8 lm W^-1,16.3%/21.1%,respectively?Strong electron-donor triphenylamine was introduced into phenanthroimidazole via the N-1 position of imidazole to design and synthesize a series of phenanthroimidazole derivatives,TPA-PI,TPA-BPI,and TPA-TPI.Theoretical calculation indicates that the obvious separation between HOMO and LUMO of TPA-TPI favorites the formation of carrier-transporting channel.Non-doped fluorescent devices using TPA-TPI as a light-emitting layer show warm white light and exhibit the maximum brightness of 31475cd m-2,the maximum efficiency of 6.93%,14.0 cd A^-1,and 9.9 lm W^-1,which is the first single-molecule white light device based on phenanthroimidazole.2Cz-PI and 2Cz-Py-PI are designed and synthesized by adjusting the ratio of the donor/acceptor(carbazole/pyridine)at the imidazole C-2 position.The introduction of pyridine groups enhances the photoluminescence efficiency of 2Cz-Py-PI and improves its carrier-transporting characteristics.The 2Cz-PI-based non-doped devices exhibit the maximum efficiency of 4.82 cd A^-1,4.71 lm W^-1,4.55%with CIE coordinate of(0.19,0.11).The 2Cz-Py-PI-based non-doped OLEDs appear better electroluminescent performances with the maximum efficiency of 5.54 cd A^-1,4.57 lm W-1,6.05%,and CIE coordinate of(0.16,0.09).