Font Size: a A A

Theoretical Study On The Optoelectronic Properties Of Cyclometalated Platinum(Ⅱ) And Iridium (Ⅲ) Complexes

Posted on:2010-03-30Degree:DoctorType:Dissertation
Country:ChinaCandidate:L L ShiFull Text:PDF
GTID:1101360275980272Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
Due to the variety of molecular and electronic structures, transition-metal complexes have become very important research contents on the aspect of catalysis, analytical chemistry, bioscience, and optoelectronic devices and so on. In the area of luminescent materials, transition-metal complexes, especially for Ir(III) and Pt(II) transition-metal complexes, can utilize both singlet and triplet excitons due to the strong spin-orbit coupling effects of the heavy transition metals, and thus they are considered as attractive electrophosphorescence materials in view of their high internal quantum efficiency. With research deepening, some questions concerning material optimum and emission mechanism, such as molecular architecture, charge transport, relationship between electronic and photophysical properties, have attracted a considerable attention. In this paper, the electronic structures and optoelectronic properties of Ir(III) and Pt(II) transition-metal complexes were investigated by quantum theoretical studies. The results suggest new theoretical basis and direction for design of novel organic materials. Our work will focus on four aspects:1. The effect ofπ-conjugated length of bridging ligand on the optoelectronic properties of several platinum(II) dimers [Pt(pip2NCN)]2(L)2+ (pip2NCNH = 1,3-bis(piperidylmethyl)benzene, L represents the bridging ligands pyrazine, 4,4'-bipyridine, or trans-1,2-bis(4-pyridyl)ethylene) were studied by density-functional method. The theoretical calculations reveal that thatπ-conjugated length of the bridging ligand provides remarkable control over optoelectronic properties of these complexes. As theπ-conjugated length of bridging ligand increases, the energies of HOMOs and LUMOs, stabilities of dimers and the largest absorption strength increase whereas the ionization potentials decrease. According to the inner reorganization energy and density of states, we presume the hole-transporting properties of these dimers are better than the electron-transporting. Moreover, the optoelectronic properties of these complexes are easy to be tailored by modifying the peripheral and central ligands. These theoretical results are beneficial to the design of new functional materials with excellent optoelectronic properties.2. Three platinum(II) complexes Pt(N^N^N)Cl (N^N^N = terpyridine), Pt(N^C^N)Cl (N^C^N = 1,3-di(2-pyridyl)-benzene) and Pt( N^N^C)Cl (N^N^C = 6-phenyl-2,2'-bipyridines) are selected to study the effect of the presence and position of phenyl group on the electronic and phosphorescent properties by using quantum theoretical calculations. The calculated results show that the presence and position of phenyl group significantly affect the molecular and electronic structures, geometry relaxation, charge distribution and phosphorescent properties. Due to the strongest feedback from Pt to phenyl group, the coordination bond length trans to phenyl group is the longest among the same type of bonds. The strongσ-donor ability of Pt-C bond makes more electrons center at Pt atom and the fragments trans to phenyl group. In the luminescent process, the direction ofπphenyl→π*pyridines charge transfer of Pt(N^N^C)Cl differs from that of Pt(N^C^N)Cl owing to the different position of phenyl group. Compared with Pt(N^N^N)Cl and Pt(N^N^C)Cl, Pt(N^C^N)Cl has the smallest excited-state geometry relaxation and the biggest emission energy and spatial overlap between the transition orbitals in emission process. The radiative rate of the three complexes is nearly the same. These lead to the largest emission efficiency of Pt(N^C^N)Cl, which agrees well with the experimental observation. Thus, based on the Pt(N^C^N)Cl, new blue emitters are designed. The complex using 3-methylimidazolin-2-ylidene to instead of pyridine groups in Pt(N^C^N)Cl may be a potential efficient blue emitting material.3. The optoelectronic properties of Ir(III) complexes with 2-phenylpyridyl and 8-hydroxyquinolate ligands, including (ppy)2IrQ, (ppy)IrQ2, IrQ3, were systematically investigated, and a comparison between the main performances (e.g. electron transport and luminescent properties) of these derivatives and the original complexes AlQ3 and Ir(ppy)3 were drawn. Both AlQ3 and Ir(ppy)3 are green emitters, whereas the derivative Ir(III) complexes can serve as a new kind of red phosphorescence emitting materials. The character of the lowest triplet excited states for these Ir(III) complexes are mainly dominated by A-quinolate ligand as evidenced by the structural relaxation between the first triplet and ground states. Although all Ir(III) complexes with the 8-hydroxyquinolate group(s) can not be employed as effective host materials in organic light-emitting diodes (OLEDs) due to their low exciton energies, these phosphorescence materials, except (ppy)IrQ2, are thought to possess excellent electron transfer performance. However, the electron transport performance of (ppy)2IrQ may be disturbed by its poor ability of electron injection. The above predicted properties of these Ir(III) complexes indicate their potential applications in OLEDs.4. The photophysical properties of diarylethene-containing 1, 10-phenanthroline ligands (L1 and L2) and their rhenium(I) complexes [Re(CO)3(L)Cl] (1 and 2) were studied systematically. As shown, the transition character of the strongest absorption band and luminescent spectrum for closed-ring complex 1 is different from that of 2, the former hasππ* character and the latter has MLCT and LLCT character. We presume the second triplet excited state contributes to the phosphorescence of 1, while the lowest triplet excited state accounts for the phosphorescence of 2. Spin-orbit coupling influences the excitation energies for d(Re)-joined transitions whereas it has negligible effect on the transition character for complexes 1 and 2.
Keywords/Search Tags:Ir(III) and Pt(II) Transition-metal Complexes, DFT, TD-DFT, Electronic Structures, Electronic Spectra, Charge Transport Properties
PDF Full Text Request
Related items