Synthesis And Characterization Of Solution-processable Red And Blue Emitters

In recent years, increasing attention has been paid to molecular electroluminescentmaterials, since they have the advantages of easy preparation, high purity and clear-cutstructure-properties relationships. Basically, there are two kinds of molecularelectroluminescent materials: vacuum deposition processable materials andsolution-processable materials. Compared to vacuum-deposited processing, solutionprocessing is much simpler and more convenient for making potentially low-cost andlarge-area devices.In this thesis, four solution-processable molecule materials based on the structures of thereference compounds1and2were designed. The purpose of the molecular design was tobalance carrier transport, and meanwhile improve color purity and efficiency. The thermal,optical, electrochemical, charge transport and electroluminescent properties of the newmolecular emitters were studied.In chapter two, two symmetrical-structure red light-emitting compounds C1and C2weresynthesized on the basis of the reference compound1. Fluorine atoms were introduced tofurther improve electron injection and transport and thereby increase luminous efficiency. Thetwo compounds had good thermal stability, amorphous morphology and good solubility.Besides, the device ITO/PEDOT:PSS(50nm)/PVK(40nm)/C1(45nm)/TPBI(30nm)/CsF(1.5nm)/Al(120nm) exhibited pure red emission with CIE coordinates (0.64,0.35), and a currentefficiency of2.35cd/A, which was higher than2.1cd/A of the OLED that consisted of thereference compound1. The results above showed that the carrier transport could be balanced and the currentefficiency could be further improved by introducing the electron-withdrawing fluorine atoms.Therefore, enlightened by the above results, we introduced electron-deficientS,S-dioxide-dibenzothiophene units to modify the reference compound2and thus synthesizedtwo asymmetrical blue light-emitting compounds C3and C4. Compound C3showed goodthermal stability and amorphous morphology, but the maximum emission wavelength in filmwas red-shifted to453nm while the maximum emission wavelength in film of the referencecompound2was437nm. Nevertheless, the solubility was just7mg/mL in toluene and4mg/mL in paraxylene, which was not high enough for solution processing. Considering thesefactors,3,7-dibenzothiophene-S,S-dioxide in C4was replaced by2,8-dibenzothiophene-S,S-dioxide, which reduced the conjugation extent. As a result, the maximum emissionwavelength in film of C4was blue-shifted by about15nm. Moreover, the alkoxyphenyldendritic block introduced on the8-position of dibenzothiophene-S,S-dioxide as well as theoctyl alkyl chain of fluorenyl were beneficial to improve solubility. The single-layer deviceITO/PEDOT:PSS(40nm)/C4(60nm, solution processed)/CsF(1.5nm)/Al(120nm) gave pureblue emission with CIE coordinates (0.155,0.11) and a current efficiency of1.26cd/A whichwas much higher than0.08cd/A of the OLED that contained the reference compound2.