| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 89 === The objectives of this thesis are to prepare a series of amorphous biphenyl-linked coumarin dimmers (2, 3, 4, 5) to circumvent the phenomenon of aggregation at solid state in the application of organic light emitting diode (OLED). In the molecules designs, we introduced either two methyl groups or phenyl groups on 2, 2'-position of the biphenyl moiety as well as four methyl group substituted on 2, 2', 6, 6'-position of the biphenyl. The steric effects of the substitutents should augment the non-planarity of the molecules and decrease the possibility of aggregation. AM1 theoretical calculations showed that the dihedral angles of biphenyl moiety varied from 60 degree,to 90 degree;depending on the steric size of the substituents. Moreover, this series of diphenyl-linked coumarin dimers possesses strong luminescent and hole-transporting properties. Synthesis of these compounds could be effectively achieved by multistep reactions, which include Ullmann, Sandmeyer, Veilsmeir reactions and followed by Pechmann condensation.
Thermo-gavimetric analysis (TGA) indicated that these new coumarin dimers have very high thermo-stability up to 400 oC. Both of powder X-ray diffraction (XRD) spectra and low temperature differential scanning calorimetry (DSC) measurements strongly supported that the compounds are indeed amorphous materials and exist high glassy transition temperature (Tg) up to 130 oC - 142 oC. Optical and redox properties of these compounds were assessed by fluorescence measurements and cyclic voltammetry (CV) respectively.
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