Synthesis And Properties Of Novel Hole Transport Materials Containing Triphenylamine Units

The hole transport material is one of the most important organicelectroluminescent materials, which could improve the injection efficiency and thetransmission efficiency of the holes in the device effectively. Since the small moleculehole transport material and the polymer hole transport material have their ownadvantages and disadvantages, seeking novel hole transporting materials which haveexcellent performance has become a very important topic.In this thesis, thirteen novel luminescent hole-transporting materials (HTMs)containing triphenylamine groups connected with different bridged bonds weresynthesized via wittig reaction. All of the compounds were characterized by infraredspectrum (IR), proton nuclear magnetic resonance (1H NMR) and high resolutionmass spectrum (HRMS) technology. The compounds show excellent solubility incommon organic solvents such as tetrahydrofuran, chloroform, and so on.The quantum chemistry calculation was performed based on density functionaltheory (DFT). The calculation result illustrated that the geometry of the titledcompounds is benefit to inhibit the crystallization of the compounds effectively. Thehighest occupied molecular orbital (HOMO) all HTMs could match with the workfunction of ITO (-4.7eV), which are suitable to the hole injection. Optical,electrochemical and thermal properties also have been investigated. The UV-Visabsorption spectra of the thirteen compounds in dilute tetrahydrofuran were measured.The compounds exhibit two absorption bonds at the region of294nm~309nm and375nm~434nm, respectively. The maxima emission peaks are located at426nm~519nm, corresponding to blue to yellow light emission. These materials have thefluorescence life between1.60ns and3.13ns. And their fluorescence quantum yieldare from22.3%to68.1%in dilute tetrahydrofuran. Cyclic voltammetrymeasurement showed that HOMO levels of these compound are in the range of-5.08eV~-5.29eV, which are proper for hole injection. Thermal properties of thesynthesized compounds were studied by differential scanning calorimetry (DSC).These compounds possess higher Tgbetween72℃and146℃, suggesting that theyhave excellent thermal stability.The synthesized compounds were prepared to organic film by spin-coatingprocess, and the films were characterized. The crystallinity of the films were studied by X-ray diffracion(XRD), the result show that these films have amorphous structure.The organic film has a smooth surface, which could be supported by atomic forcemicroscopy (AFM) images and the field emision scanning electron microscope (SEM)photograph. All of these results show that the film formability of these compoundscould be improved by increasing of the compound molecular weight and theexpanding of the conjugate system. The titled compounds were employed to fabricateorganic electroluminescent light emitting devices (OLEDs) by process vacuumdeposition or spin-coating. The film could be prepared by spin-coating process,indicating good film formability of these compounds. Small molecular weightcompounds (HTM5,7,8,11,13) were used to fabricate OLEDs with the configurationof ITO/HTL/Alq3/Al/LiF through vacuum deposition way, and the turn on voltage ofthe devices are between4.2V and9.8V, the maximal luminancce efficiencies are8723cd/m~2obtained from the device fabricated with HTM5. Larger molecular weightcompounds (HTM1,2,3,4,6,9,10,12) were fabricated OLEDs with the configuration ofITO/HTL/Alq3/Al/LiF by spin-coating way, results show that the device preparedfrom HTM10has the best performance. Its turn on voltage is5.2V, and its maximalluminancce efficiencies is846.5cd/m~2. Then we improved the configuration of device.HTM10,12and PEDOT were used to fabricate OLEDs with the configuration ofITO/HTL/P-PPV/Ba/Al. The turn on voltage of device prepared from HTM10dropped to3.25V, and the maximal luminancce efficiencies rised to103690cd/m~2.The turn on voltage of device prepared from HTM12is3.5V, and the maximalluminancce efficiencies is70941cd/m~2, both of their performance are better than thedevice prepared from PEDOT.