Theoretical Studies Of Substituent Effects On Electronic Structures And Spectroscopic Properties Of Rhenium(?) Tricarbonyl Complexes

With the rapid development of national economy, full-color displays and solid-state lighting play more and more important roles in human life. And they have drawn tremendous research interest from academia and business. In order to satisfy demand for saving energy and environmental protection, new lighting materials are constantly researched. Organic light-emitting diodes(OLED) have been developed as promising flat-panel displays and solid-state lighting devices due to their virtue of large-area fabrecation, high brightness, fast response, good flexibility, simple structure, less power consumption, non-pollution and so on. The synthesis and optimized performance of new OLED light-emitting materials will further promote the development of display and lighting technology. Both efficiency and color purity of OLED are focuses of attention in displays or lighting applications.In recent decades, phosphorescent materials containing heavy metal complexes have attracted much attention because of their good physical properties, electrochemical properties and 100% internal quantum efficiency theoretically, especially OLED luminescent material of transition metal rhenium(I) complexes. This kind of rhenium(I) complexes has many advantages, such as high room-temperature phosphorescence quantum yield, relatively short excited state lifetime, excellent thermal stability and adjustable emittinglight. So far, a large number of rhenium(I) complexes have been synthesized in experiments and their crystal structure and physical properties are also systematically studied, but the relevant theoretical researches are less.The starting points of this thesis are current problems in OLED luminescence materials and luminous characteristics of rhenium(I) complexes. On the basis of the experimental synthesis, substituent effects on rhenium(I) tricarbonyl complexes with differently auxiliary ligands have been investigated theoretically by quantum chemical calculation method. The electronic structures of the ground and excited, frontier molecular orbitals, absorption and emission spectra, ionization energy, electron affinity, reorganization energy and emission quantum yield of these metal complexes are studied from the micro electronic structure. The theoretical analysis can give the relationship between electronic structure and photophysical properties in essence. And properties of these complexes can be improved by adjusting substituent. Meanwhile material performances of designed complexes are also predicted further. We hope that our investigations can provide theoretical guidance for design, synthesis and application of new and high efficiency light-emitting materials. The main contents are as follows:1. Substituent effects on structures, absorption spectra and photophysical properties of rhenium(I) tricarbonyl complexes with imidazo[4,5-f]-1,10-phenanthroline(N^N) have been investigated theoretically by density functional theory(DFT) and time-dependent density functional theory(TDDFT) methods. The calculated results reveal that different number and positions of substituent groups can obviously change LUMO. And it further changes the absorption spectra and charge injection/transfer abilities. It is found that the introduction of-C?C(complexes 2,3,4) on N^N ligand can decrease the energy level of LUMO while introductions of-CH3 or-OCH3(complexes 5,6,7) lead to increase the energy level of LUMO compared with that of 1. And the influence of R2 position is greater than that of R1 position on LUMO energy level. The lowest energy absorption bands have changes in the order of 7 < 6 < 5 < 1 < 2 < 3 < 4. Moreover, the smallest difference between ?e and ?h of 4 indicates that it is better to be used as an emitter in OLED.2. A series of rhenium(I) tricarbonyl complexes having a general formula fac-[Re(CO)3(L)(R-N^N)](L = Br; N^N = tert-butylated pyridyltetrazole; R=-H, 1;-NO2, 2;-CN, 3;-OCH3, 4;-CH3, 5) have been investigated theoretically by DFT/TDDFT, including electronic structures, spectra properties, photophysical properties and emission quantum yield of five complexes. The results reveal that the introduction of electron-withdrawing group can decrease the energy level of LUMO, so energy gap is smaller. It makes that the lowest energy absorption and emission bands are red-shifted. And the introduction of electron-donating group can cause corresponding blue-shifted. The stronger electron-donating ability of introduced group is, the larger blue-shifted of the lowest energy absorption and emission bands is. The solvent effect on spectra indicates that the lowest-energy bands have both red shifts with the decrease of solvent polarity. Complex 4 may be suitable to be used as OLED phosphorescent material because of higher charge transfer abilities and emission quantum yield compared with that of all complexes.3. Substituent effects on electronic structures, absorption/ emission spectra, photophysical properties and emission quantum yield of rhenium(I) tricarbonyl complexes having pyrimidylsubstituted benzimidazole ligand have been investigated theoretically. The investigated results indicate that introductions of electron-donating(-NH2 and-OCH3) and-F group can increase the energy level of LUMO, so energy gap is greater. It leads to blue-shifted in the lowest energy absorption and emission bands. On the contrary, the introduction of electron-withdrawing group(-NO2) can induce obviously red-shifted. And the stronger electron-donating ability of introduced group is, the larger blue-shifted of the bands are. It's worth noting that complexes 2, 3 can emit blue-green light and their charge transfer abilities and emission quantum yield may be higher. So complexes 2 and 3 are possible to be promising candidates for blue-green phosphorescent material in organic light-emitting diodes.