Theoretical Studies On Excited State Properties & Related Applications Of Ir, Ru, And Re Complexes

Chemistry is the study of change. And we concern the change about excited state. The density functional theory based methods provide a way to explore the electronic structure of molecules. This contribution is focused on the relationship between the excited state properties and the corresponding applications of several transition metal complexes.Part A:Evaluate the dye in DSSC application, the quantum way. Solar energy, in theory, should be the answer to all our energy problems. It became the truth since Prof. Gratzel invented the third generation of solar cell, the so-called Gratzel Cell in 1991, which paves the way for us to use solar energy as the replacing energy resource in near future. The Ru(II) complexes [Ru(bpp)(dcbpy)Cl]+(1). [Ru(tcbpp)(bpy)Cl]- (2). and [Ru(tc'bpp)(bpy)Cl]+(3) are studied theoretically using DFT techniques to explore their properties as dye in solar cell. The calculation results indicate which sites the COOH groups attach can significantly influence the electronic structure of the complex. By migrating the COOH groups from the bpy ligand in 1 to bpp ligand in 2 and 3, the nature of LUMO changes from bpy-localized to bpp dominated. The calculated low-lying absorptions at A> 370 nm of the three complexes are categorized as metal-to-ligand charge-transfer (MLCT) transitions and the transition terminates at the orbital populated by the COOH appended ligand. The atomic spin density analysis also indicates that the lig-and which is modified by the COOH groups is the ideal spot for the captured electron to situate. It can be predicted that the performance of 2 and 3 in the dye-sensitized solar cell can be enhanced as compared with 1. And finally, two new dyes with expected high efficiency were found. These rules must be followed when design new dyes:i) to absorb as much light as possible, but make sure all the excited states are energetic enough to make a valid charge injection; whereas, it's useless even if the whole UV-vis region are covered, ii) The linkage group-COOH is the only bridge to pass the excited charge to semi-conductor. To make sure all the linkage groups are attached to the ligand which the LUMO appears, iii) Attaching the linkage to the proper position can tune the excited state energy levels.Part B:Excited state character and fluoride sensor. The fluoride anion is of particular interest among the range of biologically important anions due to its established role in preventing dental caries and as a treatment for osteoporosis. Chronic exposure to a less salubrious level of fluoride anion. however, can lead to dental or even skeletal fluorosis. This diversity of function, both positive and negative, makes the design of chemo-sensors for fluoride anion one of considerable current interest, i) The sensor based on singlet excited state properties, in which the chang-ing of absorption spectrum is taken as the detection signal. The detection mechanism of [(bpy)2Ru(H3ImBzim)]2+was investigated by DFT methods. The detection process is truly mastered by deprotonation mechanism, which means the detection signal might be perturbed by other Brenster base anion. ii) The sensor based on triplet excited state properties, in which existence of fluoride is evidenced by the quenching of phosphoresce or the shift of emission. The geometry, electronic structure, and spectroscopic properties together with the fluoride binding nature of the luminescent rhenium(Ⅰ) tri-carbonyl diimine complex with a triarylboron moiety, [(arB)Re(CO)3(phen)] were investigated by DFT approach. All absorptions are attributed to intra-ligand charge-transfer (ILCT) within the triarylboron ligand but being dis-turbed by some contribution of metal-to-arylboron ligand charge-transfer (MLCT) characters. Moreover, the 676 nm phosphorescence computed by TPSSh functional originates from the 3LLCT/3LMCT transition. Binding the F- results in the re-configuration of the molecular geometry and the varia-tion of the optical properties. The highest energy absorption band is intensi-fied while the lower energy absorption bands are weakened and blue-shifted slightly. The emission maximum is red-shifted to 875 nm after binding the F-. The strongly covalent bond between boron and fluoride and the hydro-gen bond interaction among fluoride atom and the adjacent hydrogen atoms of durene methyl groups are found to be the reason of the exclusive sensor ability for fluoride.We hope the current exploration can give some knowledge about the detec-tion mechanism of F- sensor and provide some inspiration for the design of functional molecular detector for F-Part C:Triplet excited state and efficient luminescence. Energy resource severely restricts the development of the world. Along with the development of new energy resource or alternative energy resources, im-proving the energy utilization is much appreciated at current stage. The high efficiency and low cost of OLED light has been widely recognized. The low purity and efficiency of blue emitter, however, drawback the further applica-tion of OLED light. Previous publications reveal that the deep blue emitter can be achieved by enlarging the HOMO-LUMO gap, however, always end up with low efficiency. But in current contribution, high efficiency blue emitter was found by modify ligand carefully.The geometries, electronic structures, and the lowest-lying singlet ab-sorptions and triplet emissions of [(fppy)2Ir(III)(PPh2Np)] (1), and the-oretically designed [(fppy)2Ir(III)(PH2Np)] (2), [(fppy),Ir(III)Np]-(3). and [(fpNHC)2Ir(III)(PPh,Np)]+ (4) were investigated with DFT based approaches. The ground-and excited-state were optimized at the PBE0/LanL2DZ;6-31G* and uPBE0/LanL2DZ:6-31G* level of theory within CH2Cl2 solution provided by PCM. respectively. The lowest absorptions and emissions were evaluated at M062X/Stuttgart;cc-pVTZ;cc-pVDZ level of theory. Though the lowest absorptions and emissions were all attributed as the ligand based charge transfer transition with slight metal-to-ligand charge transfer transition character, the nice distinction in geometries and electronic structures result in the different quantum yields and versatile emission color. Complex 4 would show a strong absorption at 310 nm and may give out weak orange-yellow emission. While 3 is expected to be highly emissive in deep blue region with emission peak at 470 nm. The closeπ-πstack of phenyl rings between P^C and phenyl-pyridine ligands, which stabilizes the triplet excited state, could be the reason for the observed extremely high efficiency. Also this strategy has been applied to tune the excited state of Ir complex with NTC ligand. Finally, another highly efficient blue emitter was found. Here is the guidance:larger HOMO-LUMO gap and eminent metal participation in emission related transition are vital for high efficient blue emitter. DFT benchmark test for transition metal Iridium complex reveals that the ap-propriate exchange-correlation functional and basis set are vital for reasonable in-terpretation of chemical properties beyond numerical results. A critical procedure is provided for selecting the proper functional and basis set for practical calculation.