Synthesis And Properties Of A Binuclear Ruthenium Bipyridyl Complex Based On Thiophene-ethynyl Bridge

According to the research progress of electroluminescent materials specially on metal complexes, two kinds of binusclear ruthenium(II) electroluminescent materials 8a and 8b with diethynyl-thiophene and diethynyl bridged were designed and synthesized. The former is novel and the latter is known. The structure of 8a and 8b were characterized by API-MS, 'H-NMR, Elemental Analysis. Their photophysical, electrochemical and ECL properties were studied by UV-vis,fluorescence spectra, cyclic voltammetry and ECL analysis.1) By using 2, 2'-bipyridine as starting material, 4-bromo-2, 2'-bipyridine was obtained through oxidation, nitration and bromination and 4-iodo-2,2'-bipyridine was obtained through oxidation, nitratio, reduction, diazotization and iodination, with total yield of 27% and 32% respectively. The yields were effectively increased by the modification of nitration and bromation. The mechanisms of nitration and diazotization were discussed.2) By using 2,5-diiodothiophene, trimethylsilylacetylene, 4-bromo-2, 2'-bipyridine and 4-iodo-2,2'-bipyridine as starting materials, 8a and 8b were obtained with total yield of 76% and 77% respectively through repeated Pd-catalyzed coupling reaction, then coordinated with cis-Ru(bpy)₂²+Cl2^-2H₂O. Compound 4-iodo-2,2'-bipyridine was applied for the Sonogashira reaction, the reaction condition was studied and the mechanism of Sonogashira reaction was discussed.3) The photophysical, electrochemical, electroluminescence properties of binuclear Ruthenium complexes 8a and 8b were studied. Compared to 8b, the maximum absorption of 8a has 6nm of red shift, while maximum emission has 5nm of red shift. On the other hand, molar absorption coefficient was increased for the same reason. The cyclic voltammogram of 8a and 8b showed the feature which were characteristic for ruthenium(H) tris-bipyridyl species. The redox potentials of 8a are nearly equaled to those of 8b. The ECL of 8a and 8b were 3.5-4 times larger than Ru(bpy)3²+in canstant voltage and 40 times larger in pulse voltage. The mechanism of ECL was discussed.