Quantum Chemistry Study On Decting By Fluorescein Series Compounds FL_n(n=1～5) And Iridium (Ⅲ) Quinoxaline Complexes

Fluorescent sensors have been the subject of considerable academic and biochemistry research in recent years because of their possible applications in the mammalian cardiovascular, immune and nervous systems. Consequently, detection of NO levels in vivo becomes a popular topic for biologists, chemists, etc.. In particular, the appearance of fluorescent probe for detecting NO molecule in vivo is of great interests to a large number of scientists. Therefore, the research on the structures, properties and absorption spectrum of such fluorescent materials is very valuable.Three red-emitting Ir(III) complexes, (fpmqx)2Ir(L) {fpmqx=2-(4-fluorophenyl)-3-methyl-quinoxaline; L= triazolylpyridine (trz) (1); L= picolinate (pic) (2) and L= acetylacetonate (acac) (3)} were introduced in the present paper. The ground-state geometries were fully optimized at DFT level using the B3LYP method, and the lowest-lying triplet excited-state geometries were calculated with the single excitations (CIS) approach. There were not any symmetry constraints during the structural optimizations. optimized by DFT with Becke's LYP (B3LYP) exchange-correlation functional and the configuration interaction with single excitations (CIS) approach. There were no symmetry constraints among these complexes. On the base of respective optimized geometries of ground and excited states, the TDDFT/B3LYP method is applied to calculate the spectrum associating with the polarized continuum model (PCM) in dichloromethane (CH2Cl2) media in order to obtain the vertical excitation energies of singlet (Sn) and triplet (Tn) states. All calculations were performed with Gaussian 03 program package.The main results are as follows:1. By using the theoretical method of DFT and TD-DFT we optimized the geometries of a series of FLn and FLnNO1, FLnNO2, FLnNO3 fluorescent materials. And we also made a detailed analysis on the changes of bond lengths and angles. Meanwhile, we explored three positions of NO+ to offense the FLnCu fluorescent probe. We demonstrated the stabilities of these structures by frequency calculations. All of the calculations on these fluorescent complexes have been performed at the B3LYP/6-31G** level using the Gaussian 03 program package. The results show that the energy of FLnNO2 generated by NO+ attacking the o-OH position was the lowest. Meanwhile, we also made a comparison test using different basis set 6-311++G** at the same B3LYP level. The results showed that influence of the increase in basis functions on the optimization is small, and the solvent effects are remarkable. We made a deep research in the absorption spectrum of above mentioned materials by means of the time-dependent density functional theory (DFT) method. Through the comparative analysis of the strengths of absorption spectrum, we can see that strong electron-withdrawing group can increase the energy of LUMO orbital, and decrease the energy of HOMO orbital, which leads to the increase of HOMO-LUMO gaps. Finally, their minimum absorption is blue shifted. Conversely, the electron-pushing group leads to red shifted minimum absorption.2. Quantum-chemistry study was applied to investigate the electronic structures, absorption and phosphorescence mechanism, as well as electroluminescence (EL) properties. Three red-emitting Ir(III) complexes, (fpmqx)2Ir(L) {fpmqx=2-(4-fluorophenyl)-3-methyl-quinoxaline; L= triazolylpyridine (trz) (1); L= picolinate (pic) (2) and L= acetylacetonate (acac) (3)} were introduced in the present paper. The calculation shows that the HOMO distribution for 1 is mainly localized on trz moiety due to its strongerπ-electron acceptor ability, and HOMOs for 2 and 3 are mainly the combination of Ir d- and phenyl ringπ-orbital. The differences of phosphorescence yields and electroluminescence efficiencies among 1-3 are also investigated in this paper. The geometrical and electronic structures, and the phosphorescence spectrum and electroluminescence properties of three Ir(III) complexes (fpmqx)2Ir(L) were investigated using the DFT and TDDFT methods. The computational results reveal that, strongerπ-electron acceptor ability of trz than pic and acac results in the HOMO distribution residing on the trz moiety for 1, and those localized on Ir d- and phenyl ringπ-orbital for 2 and 3. The lowest energy absorption for 1-3 is mainly HOMO→LUMO transition configuration. Due to the large HOMO and HOMO-1, LUMO and LUMO+1 energy gaps, all of them have mixed transition characters of MLCT, LLCT and ILCT. In addition, the higher electroluminescent efficiency of 2 than 1 and 3 comes from the relative smaller HOMO or LUMO energy differences between 2 andα-NPD and LiF/Al, which can improve the hole or electron injection efficiency and confine the recombination zone within the light-emitting layer. Certainly, other factors, such as different temperature and environment can also resulting in different phosphorescent efficiencies among these complexes.