Theoretical Investigation Of Alq₃ Grafted On PPV Units And Be Complexes Of Pyridyl Benzimidazole Derivatives On Photoelectronic Properties

Electroluminescence (EL) study in small molecules and polymer materials will become more and more important in next generation technologies. They attract considerable interests in experiment and theory. Alq₃ is considered as a very typical small molecule in organic light-emitting diodes (OLED) experiments since the first realization of a multilayered EL device by Tang and VanSlyke in 1987. Its emission spectra were considered from the parts of ligands. Thus its academic investigations are discussed, for example some substitutional groups were joined on the 8-hydroxyquinoline or Al was replace by others metalsEL from Ï€-conjugation organic polymers has lately been attracting a great deal of attention for academic interests as well as industrial interests since the Cambridge group's report in 1990 on the EL properties of PPV. PPV has been studied extensively due to their high fluorescent yield and stability. Current research is concerned about changing substitute of PPV chain to obtain perfect emission spectra or improving illuminant intension and efficiency But the obstacle lies in the rapid increasing of computational costs as the systems become larger and more complex. The computational time tCPU is proportional to certain power of the system size, i.e., tCPU∝ Nx, where N is the number of electrons, and x is an exponent which is usually larger than 1. For instance, the computational time of ab initio Hartree-Fock (HF) molecular orbital calculation has an O (N³⁴) scaling. The localized density matrix theory (LDM) had been developed by G. H. Chen group. LDM method is the linear-scaling quantum chemistry method by simulating molecular excited state properties, such as optical, electric and magnetic properties, even in the large molecular systems. The method based on the time-dependent Hartree-Fock (TDHF) approximation which includes all single electron excitations and partial double, triple and the other multiple electron excitations15 and "the nearsightedness of equilibrium systems" Electronic properties of polymerized Alq₃ and 8-hyroxyquinoline linked with PPV units were characterized by LDM method in chapter 3. In chapter 4, electronic properties of transition of 2-(2'-Pyridyl) benzimidazole Derivative and their Be complexes were investigated with the same method. The main conclusions of chapter 3 are in the following: (I)The results from the FMOs, the absorption spectrum and density matrices are generally coherent. The largest absorption spectrum appears as red shift from the 8-hydroxyquinoline, PPV-Alq3, PPV-hydro to PPV (II)For mainly discussed PPV-Alq₃, absorption peak is about 3.00 eV, i.e. 413 nm near the purple light. Two 8-hydroxyquinolines have very slight effect on electronic transition. (III)With the increasing of length extension of molecule and Ï€-conjugation, the first absorption peak shown red shift. Among the molecules PPV linked with Alq3 units, PPV-hydro3 possesses lowest energy gap is 2.77 eV, i.e.447nm near the blue light. The main conclusions of chapter 4 are in the following: (I) Although the absorption peaks show red shift through adding the benzene between the 2-(2'-Pyridyl) benzimidazole of two sides, but it change luminescence principle of pmbp. 2-(2'-Pyridyl) benzimidazole would not have contribution of electronic transition. (II) Comparing with the first absorption peak of bmbp2, that of the new molecule that is from two bmbp molecules through Ï€-Ï€ stack appear 2nm red shift. It comes from the interaction between two different 2-(2'-Pyridyl) benzimidazole. (III) For two mainly discussed Be-2-(2'-pyri) benzimid and Be-bmb, Be-bmb has excellent property of luminescence. It is 436nm in the blue region. Electronic transition is between the Be-2-(2'-pyri) benzimid on one side and two benzenes coordinating with Be on the same side.