| In recent years, organic light-emitting devices (OLEDs) have attracted muchattention in the fields of science and industry as new generation of display technology.The researches on OLEDs have acquired sufficient developments, and OLEDproducts have appeared for commercial application. At the present, many reportedhigh-performance OLED devices adopt doping technology in preparing light-emittinglayer (EML). However, successful doping requires precise control over the dopantconcentration, which could increase the manufacturing cost, and it is unfriendly to theindustrialization for OLED technology. Moreover, the phase separation and energytransfer in the dopant-host system could also affect the performance and stability ofthe doped device. Comparing with doped ones, the non-doped OLED devices avoidthe influence of dopant concentration, increase the stability, repeatability and lifetimeof the devices, and reduce the difficulty of processing, which is suitable for masscommercial production. But few emitting materials for high-efficiency non-dopedOLED devices are reported, for they need possessing the properties of highluminescent efficiency, favourable emitting color and excellent carrier-transportingability. Therefore, it is necessary to search new fluorescence materials for non-dopedOLEDs. On the other hand, organic fluorescence molecules always possess theπ-cojugated aromatic cores, which makes them easy to form ordered supramolecularself-assembly morphologies through π-π and other weak interactions after beingproperly modified. These multifunctional organic materials with properties ofelectron-transproting, optoelectrons, supramolecular self-assembly and so on havepotential applications in many fields, which made them one of the most popularhotspots for scientific researcher in recent years. In this paper, we designed and synthesized new fluorescence materials for non-doped OLEDs and self-assemblybuilding blocks with high luminescent emission by modify parent molecules of7,14-diphenylacenaphtho[1,2-k]fluoranthene (DPAF) and7,8,9,10-tetraphenylfluo-ranthene (TPF) with appropriate functional groups. And we systematically researchedthe physical and chemical properties of the obtained derivatives, and discussed therelation between their performances and the internal molecular structures.1. In chapter II, we introduced four N-containing electron-donating groups suchas diarylamines and carbazole to the both ends of DPAF, and obtained four D-A-Dtype N-containing electron-donating groups substituent DPAF derivatives. TheseDPAF derivatives possess twisted molecular configurations and separated frontiermolecular orbitals of HOMO and LUMO as a result of the introduction ofend-capping N-containing electron-donating groups, which make them displayexcellent phase and thermal stabilities, high fluorescence quantum efficiencies insolid states, and perfect transporting abilities for both holes and electrons. We used allfour DPAF derivatives as EMLs for non-doped green OLEDS, and the devices ofthem, especially DPAF-Cz, all exhibited favourable performance, suggesting thepotential applications of N-containing electron-donating groups substituent DPAFderivatives in the fields of OLEDs.2. In chapter III, we introduced the N-containing electron-donating groups suchas diarylamines and carbazole to the parent molecule TPF, instead of DPAF, andobtained three D-A-D type N-containing electron-donating groups substituent TPFderivatives. Compared with the DPAF derivatives, the aromatic cores of the obtainedTPF derivatives have less π-conjugation, and the rigidities of their molecules reducealong with the distortion of the configurations, which induce that they possess goodfilm-formation properties, their thermal stabilitis reduce a little, the LUMO energylevels of them increase obviously, and their emissions exhibit clear blue-shifts,compared with DPAF derivatives. At the same time, these TPF derivatives alsomaintain the twisted molecular configurations, separated frontier molecular orbitals ofHOMO and LUMO, high fluorescence quantum efficiencies in solid states, andperfect transporting abilities for both holes and electrons. These properties indicate these TPF derivatives also have the potentials to be good emitting materials fornon-doped OLEDs. And we choose TPF-DPA and TPF-Cz as EMLs for non-dopedblue OLEDs, of course, both of them showed high-performances.3. In chapter IV, we designed and synthetized three short-chains substituentderivatives DPAF-n (n=1,2,4) by introducing three kinds of phenyl with differentsmall alkoxies to both ends of parent molecule DPAF. The characterization ofphotophysical properties showed that the introduction of alkoxies has no affect on theabsorption and fluorescence properties of parent molecule DPAF, the derivativesDPAF-n (n=1,2,4) all exhibit perfect luminescent properties. We tried self-assembly growth of these short-chains DPAF derivatives by using common methods,and the results showed that DPAF-n (n=1,2,4) had different properties of self-assembly. The compound DPAF-1was inclined to form the crystals of microrods,while the DPAF-2was easy to assemble to be microsheets. Many architectures couldbe formed by DPAF-4, and parts of them had weak flexibilities. As the attachedchains became longer, the influence on the processes of self-assembly increasedobviously by the external conditions such as polarities of solvents, concentrations ofsolutions and so on. By analyzing the crystal structures of DPAF-1and DPAF-2, wecan conclude the molecular packing of these short-chains DPAF derivativesdetermine their self-assembly morphologies formed.4. In chapter V, we introduced flexible long alkoxies to parent molecule DPAFand obtained three long-chains substituent derivatives DPAF-n (n=8,12,16). Thecharacterization of photophysical properties confirmed that the introduction ofalkoxies has no affect on the electronic energy level of parent molecule DPAF, but ithas impact on the molecular packing modes of DPAF-n derivatives with differentlengths of chains in solid states. Since the introduced chains became longer, theproperties of self-assmbly of DPAF-n (n=8，12，16) were quite different from theshort-chains DPAF derivatives that are easy to form crystalline micro-/nano-structures. Most of the assembling morphogies of DPAF-8were still crystalline, andthe obtained DPAF-8flexible microribbons were always flat and thin. And twistedmicrowires based on DPAF-12were readily achieved by phase transfer or slow evaporation with appropriately regulations. For compound DPAF-16with longeralkyl chains, the thinner nanofibers with twisted morphologies were formed. Theassembly conditions such as the concentrations of solutions, polarities of interfaces,rates of evaporations, had significant effects on the forming of the twisted characters,which could make the twisted twisted properties of the obtained micro-/nano-structures disappear, or even make the flexible morphologies change to becrystalline. By comparison of the emission spectra and XRD patterns of DPAF-n (n=8，12，16) samples in different states, we can infer the molecular packing should bedifferent in flexible and crystalline architectures. And from the analysis of singlecrystal structure of DPAF-8, we find a kind of molecular arrangement with obviouslyhelical features in the crystal at the supramolecular point view, which demonstrates apossible explanation for the formation mechanism of twisted wires in this study.In summary, we have carried out a series of functional modification base onfluoranthene derivatives DPAF and TPF, designed and synthesized new compoundsused as OLEDs materials and self-assembly building blocks with high-efficiencyluminescent emissions, characterized their properties systematically, and theninvestigated the relationship between their performances and internal molecularstructures. These researches expand the types of emitting materials for non-dopedOLEDs, and obtained various controllable luminescent self-assembly morphologies,which have potential applications in the fields of optoelectrons, semiconductors,bio-sensors, and so on. |
PDF Full Text Request