Synthesis And Optoelectronic Properties Of Organic Small Molecules, Oligomers And Dendrimers

Organic light-emitting diodes(OLEDs)have attracted intensive interest due to its potential application in the large-scale,full-color plat displays.Great efforts have been paid by both academic and industrial researchers to develop new organic light-emitting materials that can meet the commercial use.In this paper,a series of highly fluorescent compounds consist of simple fluorophores and triple bonds have been synthesized and characterized.A Pd/Cu-catalyzed Sonogashira coupling reaction is used as a key reaction.Their application in OLEDs is investigated.Moreover, fluorescent structure-property relationships of these compounds have been discussed.First,a series of organic small molecules composed by pyrenes,fluorenes and carbazoles are synthesized and characterized.These compounds exhibit strong blue photoluminescence(PL)with high PL quantum yields,good thermal stabilities. OLEDs fabricated with these compounds by simple spin-coating exhibit blue electroluminescence(EL),which indicates these small molecules might be good blue light-emitting materials.Second,a series of fluorescent,well-defined oligomers have been synthesized and characterized.These oligomers contain pyrene-modified oligofluorenes, pyrene-modified oligocarbazoles,and fluorene/anthracene-alternative oligomers.With regards oligofluorenes and oligocarbazoles,the introduction of pyrene improves the PL quantum yields of compounds.Moreover,the different positions of pyrene on the oligomer backbone can result in different emission color.Both of oligomers exhibit good EL properties,especially pyrene-modified oligomers that show good light-emitting properties and hole-transport abilities.The fluorene/anthracene-alternative oligomers exhibit yellow PL and EL emission. Devices using these compounds as dopants exhibit a maximum efficiency of 10.69±0.27 cd/A with a brightness of 1400 cd/m²,and a maximum brightness of 22037 cd/m² at 7 V.which indicates they are promising light-emitting materials for OLEDs.Furthermore.a series of fluorene-centered oligocarbazoles have been synthesized and characterized.These compounds show strong blue emission in solution and high glass-transition and decomposition temperatures.They exhibit blue EL emission at low voltages,but when the voltage increases,they exhibit whit EL emission with broad spectra that almost cover the range of the visible light.Such a white light is considered as a combination of blue light from excimers and orange light from electromers.Third,a series of conjugated,solution-processable dendrimers have been synthesized and characterized.These dendrimer show strong yellow fluorescence, good thermal stabilities and film-forming properties.Single-layer devices (ITO/PEDOT/dendrimers/Cs₂CO₃/Al)based on these dendrimers show a maximum brightness of 5590 cd/m² at 16 V,and a maximum efficiency of 2.67 cd/A at 8.6 V. To the best of our knowledge,this is the best results approached so far on electroluminescent devices using dendrimers as a single active layer,further indicating that acetylene linked dendrimers should not be excluded out of the filed of OLEDs.Moreover,in order to improve the device performances through balancing the holes and electrons in the devices,fluorine atoms are introduced at the periphery of dendrimers.The devices based on fluorine-modified dendrimers exhibit lowered turn-on voltages.Interestingly,one fluorine-modified dendrimers exhibits facile nanofiber self-assembling properties.Finally,totally 144 compounds including 120 new compounds have been synthesized and characterized,many of which exhibit excellent PL and EL properties indicating they are promising light-emitting materials.This work will undoubtedly enrich the field of optoelectronic materials.