First-principle Study Of Alq3 And Its Derivatives

OLEDs receive much attention due to its unique properties. Tris (8-hydroxyquinoline) aluminum (Alq3) has been a popular compound because of its green emission, good electron mobility and thermal stability up to 350℃. However, as an efficient green emitter with emission maximum in the range of 526nm, Alq3 could not meet the requirement of full-color display. To search for the luminescent materials with different emission waves, many researches have been carried out on Alq3-like complexes. In the work, Alq3 and its derivatives were studied by using the first-principle theory, and the specific contents of the dissertation are as follows:(1) The structures of tris(8-hydroxyquinoline) aluminum (Alq3) and its difluorinated derivatives were optimized for the ground state at the B3LYP/6-31G* level and for the excited-state at the CIS/6-31G* level. At the same time, the absorption and emission spectra based on the above structures were calculated by the time-dependent density functional theory (TD-DFT) using the PBEO method with the 6-31G* set. In comparison with the structure of Alq3, there are slightly change in the difluorinated derivatives. The HOMOs and LUMOs of the derivatives are analogous with Alq3. The HOMOs are mostly localized on L3 ligand but rarely on L1 ligand while the LUMOs are localized mostly on L1 ligand. The 3,5-difluoro,3,7-difluoro and 4,5-difluoro substituted Alq3 induce energy gaps narrow and spectra red-shift, while the 3,6-difluoro,4,6-difluoro and 4,7-difluoro substituted Alq3 induce energy gaps wide and spectra blue-shift. Also the carrier transfer properties were calculated.(2) The geometries and electronic structures of 2Meq2AlOC6H4R and its derivatives were fully optimized using B3LYP with 6-31G(d) set. The structures of derivatives have been changed slightly. The LUMOs are mostly localized on A and B but rarely on C while the HOMOs are localized mostly on C and the metal Al doesn't contribute to HOMO and LUMO. The substitutions of electron-withdrawing groups increase the gap and the substitutions of electron-donating groups decrease the gap. Also the substitutions of electron-withdrawing groups enhance the electron injection ability. The reorganization energies of 2Meq2AlOPh and its derivatives are calculated, all complexes are better charge transport materials.(3) The structures of tris(8-hydroxyquinoline) aluminum (Alq3) and its difluorinated derivatives were optimized for the ground state at the B3LYP/6-31G* level and for the excited-state at the CIS/6-31G* level. At the same time, the absorption and emission spectra based on the above structures were calculated by the time-dependent density functional theory (TD-DFT) using the PBEO method with the 6-31G* set. The HOMOs and LUMOs of Gaq3 are analogous with Alq3. The metal only plays a role of supporting and restricting ligand and makes the ligand become more rigid. It doesn't contribute to HOMO and LUMO. A red shift was predicted for Gaq3.