Synthesis And Properties Study Of D-A And A-D-A Picolinic Acid Derivatives With Non-conjugated Connection And Their Cyclometaled Complexes

The development history and status of electrophosphorescent materials and their devices are reviewed. In order to solve the current issues in the blue, red and white electrophosphorescent materials and devices, three series of cyclometalated complexes using the donor-acceptor (D-A)- and acceptor-donor-acceptor (A-D-A)- based picolinic acid as ancillary ligands with non-conjugated connection were designed and synthesized. The optophysical and electrochemical properties of cyclometalated complexes were studied. The key works are listed as followed.1. Three series of cyclo-metalated complexes were synthesized by Williamson reaction and Miyaura-Suzuki coupling reaction. Their molecular structures were characterized by 1H NMR, 13C NMR and element analysis.2. The thermal properties of these cyclometalated complexes were also studied by thermo-gravimetric analysis (TGA). The onset degradation temperatures (Td) for 5% weight loss of these red-emitting materials are above 230℃, which of these blue materials are all above 250℃, the Td of P8 is even over 300℃. The Td of these platinum complexes are all over 250℃.3. The electrochemical properties of these cyclometalated iridium complexes were studied by cyclic voltammeter. The highest occupied molecular orbit energy levels (EHOMO) were calculated based on the empirical formula. The EHOMO of the red-eimitting materials are all at about -5.3 eV, which matching the EHOMO of PVK. And the EHOMO of the blue-emitting materials are between -5.65 and -5.70 eV, which are suitable with the EHOMO of PFO.4. The photophysical characterization of the cyclometalated complexes were also researched in this paper. Incorporating triphenylamine group or bipolar transporting group(i.e. triphenylamine and oxadiazole group) into ancillary ligand of picolinic acid with a non-conjugated connection has few influence on photoluminescence (PL) spectra of their cyclometalated complexes in the dichloromethane. However, it can make the PL emission spectra much blue-shift in their neat films,The investigation has laid a well foundation for further study of the cyclometalated complexes using the D-A- and A-D-A- based picolinic acids as the ancillary ligands with non-conjugated connection. Simultaneously, the study can promote the development of the blue, red and white electro-phosphorescent materials and their devices.