Design And Synthesis Of Organic Fluorescent Emitters Based On Phenanthro[9,10-d]imidazole And Their Electroluminescence Properties

As a new generation of display technology,organic electroluminescent technology has attracted widespread attention due to its low energy consumption,wide viewing angle,fast response,easy flexibility and other advantages.With the unremitting efforts of researchers,it has stepped in the preliminary stage of industrialization.Organic light-emitting devices(OLEDs)have been considered as the most competitive candidates for new generation full-color flat-panel displays and future energy-saving lighting sources owing to their unique features.For the fabrication of both flat-panel displays and solid-state lighting sources,multicolor luminescent materials are indispensable to guarantee the quality of the devices.The core of OLED technology is luminescent materials.Hence,to fulfill these purposes,three kinds of luminescent materials emitting primary colors Red,Green,and Blue are generally employed according to the primary-color theory.Among the primary-color luminescent materials,the blue and red emitters generally show a noticeably inferior electroluminescence(EL)performance than the green materials with regard to efficiencies,lifetime,color purity,and charge-carrier injection/transport.Therefore,the continuous development of high-efficiency blue and red fluorescent materials is of great significance to the advancement of the OLED industry.Phenanthro[9,10-d]imidazole is a classical electroluminescent material construction group,which is formed by incorporating the imidazole group at positions 9 and 10 of phenanthrene.The large conjugated rigid structure of the phenanthrene plane facilitates the increase of the radiative transition rate so as to improve the luminous efficiency.Moreover,its derivatives have the advantages of simple synthesis,facile modification,good thermal stability,and relatively balanced carrier injection/transport capability,and thus have been drawn extensive attention from scientific researchers in the field of organic optoelectronics.In this dissertation,,this efficient luminescent group was used as a basic structuring unit to design and develop four types of solution-processable deep blue light-emitting polymers and two kinds of red emitters with D-?-A-?-D structure.The relationship between the structure and properties of these materials has been studied in detail.The research contents of this dissertation are summarized as follows:1.A series of wide bandgap polymers using tetraphenylsilane as the main chain and phenanthro[9,10-d]imidazole(PPI)as the side chain were designed and successfully synthesized via Suzuki coupling reactions.Herein,we report the synthesis,photophysical properties,electrochemical and electroluminescent characterization of these four polymers.The results show that the silane group provides the polymers with wide bandgaps,and PPI unit entitles the polymers with high quantum efficiencies deep blue light emission.Among them,the device using P1 as emissive layer shows the best performance with a relatively high external quantum efficiency of 0.65% and deep blue CIE coordinates of(0.163,0.099).2.Using phenanthroimidazole as a donor,and adjusting the electron-withdrawing ability of the acceptor nucleus,two kinds of double-bridged phenanthroimidazole derivatives PIDSB and PIDPh of D-?-A-?-D structures were synthesized with 2,2'-(1,4-phenylene)diacrylonitrile and 2,3-diphenylfumaronitrile as the acceptors,respectively.Both materials were red emitters.The non-doped devices based on PIDSB and PIDPh have a low turn-on voltage(3.2 V),the emission peaks are at 580 nm and 640 nm,respectively,and the external quantum efficiencies are 4.75% and 2.06%,respectively.They show more excellent electroluminescent properties in doped devices.The emission peaks were located at 540 nm and 580 nm,respectively,and the external quantum efficiencies were 6.53% and 5.30%,respectively.