Theoretical Studies Of The Spectroscopic Properties Of Re(bpy)(CO)₃(C≡CR)(bpy=2, 2'-bipyridine; R=H, CH₂OH, And C₆H₅)

Recently, the scientific researchers endeavor to design and develop new type of luminescent devices with high efficient, high stability, high brightness. The transition metal materials have good performance, such as long luminescent life and single color. Particularly, the rhenium(I) diimine complexes have been well studied because they can serve as excellent emitters, photocatalysts, and building blocks for supramolecules. Furthermore, the introduction of the acetylide moieties into the rhenium(I) diimine system would render the metal center more electron rich, with the additional advantage of raising the energy of the d-d states which would improve the population of the MLCT state.In this thesis, the ground-state structures of the Re(I) acetylide complexes were carried out using density functional theory (DFT). The nature and the energy of singlet-singlet electronic transitions have been obtained by the TD-DFT/PBE1PBE calculations upon the optimized geometries. The excited geometries were optimized by the ab initio (CIS) method. Based on the excited geometries, the emission spectra were investigated. The theoretical studies show that the modification of chemical structures could greatly modulate and improve the electronic and optical properties of light-emitting materials. The following is the main results:Electronic structures and spectroscopic properties of Re(bpy)(CO)₃(C≡CR) (bpy = 2,2'-bipyridine; R = H (1), CH₂OH (2), and C₆H₅ (3)) were studied by the ab initio and DFT methods. The ground- and excited-state structures were optimized by the DFT-B3LYP and CIS methods, respectively. The absorption and emission spectra in the dichloromethane solution were calculated by the TD-DFT method at PBE1PBE level associated with the PCM model. The calculated results indicated that the variation of the substituents on the acetylide ligand slightly changes the structures in the ground and excited states but leads to a great difference in the electronic structures. The HOMOs of 1-3 are sensitive to the change of the substituents on the acetylide ligand, and the energy levels of HOMOs are increased obviously with the introduction of the electron-donating groups; but those of the bpy-based LUMOs vary slightly. The lowest-energy absorptions arising from the HOMO-1→LUMO transitions for 1-3 were attributed to the singlet d(Re)/Ï€(C≡C)/p(CO)→π*(bpy) charge transfer (MLCT/LLCT) transitions, while the lowest-energy emissions were attributed to the triplet d(Re)/Ï€(C≡CR)/p(CO)→π*(bpy) charge transfer (³MLCT/³LLCT) transitions. The low-lying absorptions (311 (1), 323 (2), and 341 nm (3)) with the MLCT/LLCT and MLCT/LLCT/ILCT characters and the lowest-energy emissions for 1-3 are red- shifted in the order 1 < 2 < 3 when the electron-donating groups are introduced into the acetylide ligand, but the lowest-energy absorptions with MLCT/LLCT character for 1-3 and the intense absorptions (281 (1), 281 (2), and 283 nm (3)) with ILCT character are almost not changed. By comparison of the results obtained using the different functionals embedded in the TD-DFT method, the calculated results indicated that the PBE1PBE functional is appropriate for the Re(I) acetylide complexes to get the relatively satisfactory results.