Cationic Iridium Complexes With Biimidazole As The Ancillary Ligand Applied In Light-Emitting Electrochemical Cell

In order to meet the increasing demand of information, information display technologybecomes more and more attractive. As the information display technology research andexploration developing, we have found that the solid light-emitting electrochemical cells（LEC） is the advanced display technology, its further study has caught people’s attention.There has been making a big effort for Light-emitting electrochemical cells （LECs）,owing to it offer advantages over traditional organic light-emitting devices （OLEDs）, inparticular, simpler architectures and production, LECs are more and more popular. Morever,ionic transition metal complexes （iTMCs） based LECs exhibit high luminance and effciency,in addition to their good thermal and chemical stability. Among the iTMCs, cationicIridium（III）-cyclometalated complexes（CICCs） in terms of their short excited-state lifetimes,color tuning and high photoluminescence quantum yields have drawn the most attention andemerged as promising candidates for LEC applications. The frst LEC based on ionic iridiumcomplexes was reported in2004. Up to now, different color have achieved in solution,however, to achieve the goal of full-color displays, there always exist challenge for emittingin film. At the same time, effciencies, stability and response times are always criticallyimportant target for practical applications and greatly needed improved. So we should changethe structure of the complexes.Based on cationic iridium complexes’ structure, the ancillary ligands play a crucial role inincreasing the effciency and lifetime of device. By tailoring the ancillary ligands, thephotophysical and electrochemical properties of the cationic iridium complexes can be fnelytuned. Imidazole-type ligands contain two protons, they have excellent electronictransmission performance, when the two lively hydrogen protons are replaced, derivativesolubility increases and the coordination ability strengthens, which can be synthesized morecomplexes. By changing the substitution group, the complexes of photoelectric properties arechanged.Therefore, in this paper imidazole-type ligands which have been synthesized will be usedto coordination with iridium, finally we get four ionic iridium complexes. We fabricatelight-emitting electrochemical cells based on the four complexes as emitting layer respectively,and study their photoluminescence and electroluminescence properties in detail.The main contents of the article are as follows:1. We designed and synthesized four imidazole-type ligands, and reacted with cyclicmetal iridium ligands, finally we got four ionic iridium （Ⅲ） complexes. They are[Ir（dfppy）₂（bimptf）]⁺（PF₆^-）（complex1）,[Ir（dfppy）₂（bimtp）]⁺（PF₆^-）（complex2）,[Ir（ppy）₂（bimptf）]⁺（PF₆^-）（complex3） and [Ir（ppy）₂（bimtp）]⁺（PF₆^-）（complex4）, where ppy isphenylpyridine and dfppy is2-（2,4-difluorophenyl） pyridine as the cyclometalated ligands, bimptf is1,1’-bis-（3-trifluoromethyl-phenyl）-1H,1’H-2,2’-biimidazolyl and bimtp is1,1’-di-thiophen-2-yl-1H,1’H-2,2’-biimidazolyl as the ancillary ligands. All the complexes arecharacterized by IR, NMR, single crystal structure and other characterization.2. We study the four complexes of ultraviolet absorption, photoluminescence propertiesand electrochemical properties, through the quantitative calculation, we explain itsphotophysical and electrochemical properties relationship between the structure of thecomplexes.3. Based on the four complexes as emitting layer respectively, we fabricatedlight-emitting electrochemical cells, and from the device electroluminescent spectra, CIEcoordinates, life and current density and so on, device performance were characterized.