The Synthesis And Optoelectronic Propetries Of Electrofluorescence Molecules With Pendent Triphenylamine Groups

The research about Organic Light-Emitting began in the1960s. Because of thegreat potential applications in flat panel display and solid-state lighting, organic light-emitting diodes(OLEDs) have attracted widespread attentions for half a century. Asis known to all, material is the key factor which determines the performance ofOLEDs. In this thesis, we designed and synthesized three fluorescent oligomerTANzA, TABzA and TAPA which could realize RGB（red, green, blue）emissionseparately. Our design principles are as follows: firstly, we changed differentemissive core units (naphthalene thiadiazole, benzo thiadiazole and spirofluorene)based on the fluorene trimer with high fluorescence quantum efficiency in order toachieve light color adjust-ment; secondly, we substitute the alkyl chains of sixcarbon at C-9of fluorene, which offers flexibility and possibility of fabricatingdevices by solution process; thirdly, we attached triphenylamine groups at the end ofthe alkyl chains, so that the molecular can facilitate a injection and transport of bothholes and electrons. The design allows that the oligomer combines the advantages ofpolymer and small molecule light-emitting materials. Triphenylamine group, whosecentral nitrogen atom has a strong electron-donating ability, have been widely usedin bipolar light-emitting material, bipolar host material and electrode supportingmaterial as a typical hole-transport group. But the synthesis of alkyl-linkedperipheral triphenylamine groups into the C-9has not been reported in smallmolecules. The thesis explored related synthesis method and conditions. Wediscussed the effects on the properties of material by incorporating triphenylaminegroups after all characterization done. Photoluminescence characterization provedthat the red, green and blue light emitting material were obtained as expected;Electrochemical characterization proved that the HOMO level of the oligomerslower as much as PEDOT because of the incorporation of triphenylamine groups,which reduces the hole injection barrier, and this result agreed with the results ofmolecular orbital simulation; Thermal properties character ization told that the glass transition temperature (Tg) of these three oligomers are about10℃lower than thoseof carbazole substituted oligomers, and this is because the three-dimensionalstructure of triphenylamine, compared with plane rigid carbazo le, can significantlyincrease the flexibility of the molecule; AFM proved that the oligomers can formsmooth film. We also prepared spin-coating electroluminescence (EL) devices usingRGB molecular as emitting layer, The single-layer devices of TABzA (G) performedbetter: the current efficiency was2.3cdA-1, and the power efficiency was1.62lmW-1.Significant improvement was achieved by inserting the electron injection layer TPBi.The performance of double-layer spin-coating device of TABzA is as follows:current efficiency is6.4cdA-1, the power efficiency is4.03lmW-1. The EL deviceperformance of TANzA and TAPA is not ideal, so efforts need to be made tooptimize the preparation conditions.