Ionic Small Molecule Design, Synthesis, Characterization And Optoelectronic Properties Of Polymer Iridium Complexes

Charged indium (Ir) complexes have many other features except for high quantum efficiencies and easily tunable emission wavelength that may make them one of the finest candidates for lightings, displays, and light-emitting electrochemical cells (LEC). First, the synthesis condition of charged Ir complexes is much milder than that of neutral ones. Second, inert metal electrodes resistant to oxidation in air, such as Au and Pt, can be used in efficient devices based on charged Ir complexes. Third, further improving the stability of devices can be expected due to their excellent redox stabilities. In addition, charged Ir complexes are endorsed with the properties of charge transfer, consequently lowering power consumptions of devices. However, for the blend system of charged Ir complexes doped into hydrophobic host materials, the problem of phase separation is more serious than that of the system of neutral Ir complexes due to the poor compatibility, and this problem is an obstacle to their applications in organic electronics. An efficacious solution to this problem is to modify the structure of ligands or introduce phosphorescent dye into the polymer chain by grafting. Since the properties of excited states of charged iridium complexes are complicated, it is of significance to synthesize conjugated polymers with charged iridium complexes in the backbones and to investigate the relationship between chemical structure and photophysical properties. This dissertation is comprised of the following four parts.1. A series of charged diiminoiridium complexes [Ir(piq-C(?)N)₂(L-N(?)N)](PF₆) and [Ir(Fiq-C(?)N)₂(L-N(?)N)](PF6) were prepared, where piq is 1-phenylisoquinolinato, Fiq is l-(9,9-dioctylfluorene-2-yl)isoquinolinato, and L-N(?)N are bidentate N-coordinating ligands: 2,2'-bipyridine (bpy), 5,5'-di(9,9-dioctylfluorene-2-yl)-2,2'-bipyridine (FbpyF), 4,4'-dimethyl-2,2'-bipyridine (4mbpym), 5,5'-dimethyl-2,2'-bipyridine (5mbpym), 5-(thiopen-2-yl)-2,2'-bipyridine (tbpy),5,5'-di(thiopen-2-yl)-2,2'-bipyridine (tbpyt), and 5,5'-dibromo-2,2'-bipyridine (BrbpyBr). All of the complexes were characterized by ¹H NMR, MALDI-TOF and elementary analysis. X-ray diffraction studies of [Ir(piq)₂(4mbpym)](PF₆) revealed that the iridium center adopted a distorted octahedral geometry. Photophysical and electrochemical properties of these complexes were investigated and the complexes with different ligands showed different optoelectronic properties. The emissionwavelengths of the complexes could be tuned by changing the substituents on 2,2'-bipyridine. All complexes exhibited intense and long-lived emission. The excited states of ³MLCT, ³LLCT and ³LC existed simultaneously in each complex. But LLCT mixing strongly with ³LC have more contribution for complexes based on piq and MLCT mixing strongly with ³LC have more contribution for complexes based on Fiq according to electrochemical, photophysical properties, and DFT calculations. The complex with alkyl-fluorene, [Ir(piq)₂(FbpyF)](PF₆), shows high quantum yield and was expected to be a good candidate for lighting and display applications. Non-doped devices using it as light-emitting layers were fabricated and red phosphorescence was demonstrated.2. A series of Ï€-conjugated chelating polymers with charged indium complexes in the backbones were synthesized by Suzuki polycondensation, leading to homogeneous polymeric red-phosphorescence materials and chelating polymers obtained are characterized by ¹H NMR, ¹³C NMR, and elementary analysis. The fluorene and bipyridine segments were used as polymer backbones. 5,5'-Dibromobipyridine served as a ligand to form a charged iridium complex monomer with 1-(9'9-dioctylfluorene-2-yl)isoquinoline (Fiq) as the cyclometalated ligands. Chemical and photophysical characterization confirmed that Ir complexes were incorporated into the backbones as one of the repeat units by means of the 5,5'-dibromobipyridine ligand. Photophysical and electrochemical properties of these chelating polymers were investigated. Efficient energy transfer from the host fluorene segments to guest Ir complexes was realized in the solid state. In the films of corresponding blend system, however, energy transfer was not complete even when the content of Ir complexes was as high as 16 mol%. Both intra- and intermolecular energy transfer processes existed in this host-guest system, and the intramolecular energy transfer was a more efficient process. All chelating polymers displayed good thermal stability, redox reversibility, and film-forming ability. These chelating polymers showed more efficient energy transfer than the corresponding blend systems and the way that incorporation of the charged Ir complexes into the Ï€-conjugated polymer backbones efficiently avoided the intrinsic defects of blend systems, offering promising opportunities in optoelectronic applications.3. 2,2'-Bipyridine in the main chain of chelating polymer may be not coplanar because of the rotation of C-C bonds. 1,10-Phenanthroline is coplanar and red-shift of the chelating polymer emission wavelength and more efficient energy transfer can beexpected if 2,2'-bipyridine is replaced by 1,10-phenanthroline. Therefore, a series of Ï€-conjugated chelating polymers based on charged iridium complex with 1,10-phenanthroline as N(?)N ligands were synthesized by Suzuki polycondensation, which gave rise to homogeneous polymeric phosphorescent materials. 3,8-Dibromo-l,10-phenanthroline served as a ligand to form a charged iridium complex monomer with l-(9'9-dioctylfluorene-2-yl)isoquinoline (Fiq) as the cyclometalated ligands. The chelating polymers obtained were characterized by ¹H NMR, ¹³C NMR, and elementary analysis. Their photophysical and electrochemical properties were investigated. All chelating polymers showed good thermal stability, redox reversibility, and film-forming capability. Efficient energy transfer from the host fluorene segments to guest Ir complexes was realized in the solid state and complete energy transfer was realized when the feed ratio of Ir complex monomer was 4 mol%. Polymer light-emitting diodes using phen-PFOIr2 as the emissive layers were fabricated and saturated red-emission was obtained.4. Ï€-Conjugated polymers based on carbazole have high triplet energy and facilitate the injection of hole, so they are appropriate host materials for most iridium complexes. Therefore, carbazole units were introduced into the chelating polymer, obtaining chelating polymer (phen-PFOCzIr2) with fluorene, charged iridium complexes, and carbazole units. Polymer phen-PFOCzIr2 was characterized by ¹H NMR, ¹³C NMR, and elementary analysis and its photophysical and electrochemical properties were investigated. Polymer phen-PFOCzIr2 showed good thermal stability, redox reversibility, and film-forming capability. Efficient energy transfer from the host fluorene segments to guest Ir complexes was realized in the solid state. Polymer light-emitting diodes using phen-PFOCzIr2 as light-emitting layers were fabricated and saturated red-emission was obtained. The device based on phen-PFOCzIr2 showed better performance than that based on corresponding chelating polymers without carbazole units.