Synthesis And Optoelectronic Properties Of The Pyridine Functional Complexes

Recently, materials for photoelectric conversion have drawn intensive attention due to their good application prospects. Based on the diverse and excellent chelate capabilities of pyridines, new photoelectric active metal-pyridyl complexes were synthesized and investigated. In this thesis, eleven ruthenium-pyridyl complexes and eight new iridium cyclometalated complexes were synthesized (Please see the table attached for the molecular structures). Their optical properties were investigated in details.1. Synthesis, characteristics and photoelectrochemical properties of mixed-ligands amphiphilic ruthenium complexes1) To expand the conjugated structure and improve light harvest efficiency, six ruthenium(II) sensitizer were synthesized by introducing phenyl or 1,3,4-oxadiazolyl directly attached onto pyridine rings. The sensitizers (dye-2 and dye-3) exhibited the red-shift MLCT absorption and high molar extinction coefficients, which enhanced the light harvesting efficiency. For their spread conjugated structures by directly introducing phenyl to pyridine rings, the photocurrent per molecule of dye-2 and dye-3 were obviously improved in comparison of dye-1. The dye-sensitized nanocrystalline TiO₂ solar cells (DSSCs) based on dye-2 yielded an overall efficiency of 5.5% (AM 1.5 75 mW/cm²), which was enhanced by 22% than that of dye-1. Similarly, for new amphiphilic Ru( II) complexes with 1,3,4-oxadiazole group (dye-4, dye-5 and dye-6), the red- shift MLCT absorptions and enhanced molar extinction coefficients were observed at 556 nm. The contribution to photocurrent per molecule of dye-4, dye-5 and dye-6 showed that the introduction of 1,3,4-oxadiazole was benefit to improve photoelectric properties.2) As a secondary amine, carbazole group was introduced into phenanthrenyl ruthenium complex to improve the charge transporting properties, four relative amphiphilious ruthenium complexes (dye-7, dye-8, dye-9 and dye-10) were synthesized as photosensitizers for DSSCs. Despite of relative large space hindrance and low adsorbed amounts of dye-7, the photocurrent per molecule of carbazole-based ruthenium complex was nearly as twice as the others. It produced an overall optic-to-electric efficiency of 5.3%, which is higher than those of other three complexes (3%) under the same conditions. This fact may due to a multi-step charge transfer process resulting in a relative long-lived charge-separated state for dye-7sensitized TiO₂ electrode after visible light excitation, which directly led to an increased open-circuit photovoltage and conversion efficiency.2. Studies on ruthenium polypridyl complexes sensitive to metal ions.Because Hg²⁺ can easily combine with sulfur, the amphiphlious ruthenium complex dye-2 was used as sensor for Hg²⁺. The complex was combined quantitatively to Hg²⁺ while not to other metal ions such as Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Cu²⁺, Ca²⁺, Mn²⁺and Pb²⁺ by the molar ratio of 1: 1. Its detective limit is 0.5 ppm. A new terpyridyl ruthenium complex dye-11 with spread conjugated structure was also synthesized to detect Hg²⁺. Interestingly, this complex showed very remarkable color change from dark blue to pink (corresponding to about 70 nm blue-shift in its UV-spectra) upon the addition of mercury ion, indicating that it can be used as a colorimetric sensor for Hg²⁺.3. Synthesis, characteristics and electroluminescent (EL) properties of new iridium complexes with non-conjugated dendrimer framework.Eight new pyridine derivatives with non-conjugated dendrimer framework and their corresponding iridium cyclometalated complexes were synthesized by a simple and diverse route starting from 2-bromo-4-methylpyridine. The phosphorescence quantum efficiency and lifetime of these iridium complexes were all enhanced both in solution and in the solid with the increasing of dendrimer generation. This fact indicated that the dendrimers' three-dimensional hyper-branched structure had great protection to the core and the emanative structure also reduced the interaction between the cores of molecules. These complexes were used as emissive materials in the PLED configuration of ITO/ PEDOT: PSS/ PVK (40nm)/PFO: PBD + Ir complex (80nm)/Ba(4nm) /Al(120nm). Among them, the device fabricated by doping the complex Ppy-Ir-G2 (4 wt.-%) exhibited good green EL properties. The external quantum efficiency is 9.5% at 8.6 mA/cm² and the maximum luminance obtained is 18584 cd/m². For the device fabricated by doping the complex Btp-Ir-NG2 (2 wt.-%), the luminescence is red and the maximum luminance is 2451 cd/m² corresponding to the maximum external quantum efficiency of 6.5%.