Non-Aggregation Approaches by Functionalized Dendritic and Hyperbranched Structures to Enhance Polymer Light-Emitting Diode Properties

• Main Authors: Chung-Wen Wu, 吳中文
• Other Authors: Hong-Cheu Lin
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/44561091445737925273

博士 === 國立交通大學 === 材料科學與工程系所 === 95 === Functionalized dendritic and hyperbranched structures have been carried out to solve the aggregation-related problems by increasing the structural hindrances of Poly(fluorene)s (PF), and thus to reduce their self-aggregation tendency in the solid state. These dendronized and hyperbranched polymers possessed excellent solubility in common solvents and good thermal stability. Photophysical studies reveal the dendronized and hyperbranched polymers greatly suppress the aggregation of PF backbones and thus to induce pure blue PL emission. It was proven that HOMO and LUMO energy levels of the copolymers can be adjusted by increasing the carbazole and oxadiazole moieties in the electrochemical measurements; hence, the hole injection and electron transport were greatly enhanced. Pure blue electroluminescence (EL) spectra with narrow fwhm (full width at the half-maximum) values and negligible low-energy excimer emission bands were successfully achieved, indicating that these copolymers could be good candidates for blue light-emitting materials. Novel asymmetric/symmetric dendritic supramolecules were constructed by two kinds of (single/double) H-bonded acceptor chromophores, i.e. pyridyl/bispyridyl acceptor emitters, encapsulated with (one or two) 1,3,4-oxadiazole (OXD) dendritic donors in proper acceptor/donor molar ratios. Due to shielding effect of bulky OXD dendritic shells in H-bonded donors, the dendritic supramolecules are able to prevent acceptor emitters from spatial aggregation, and thus to induce glass-forming properties and show stronger emission intensities via H-bonds. Besides, the dendritic donors act as efficient light-harvesting antennae capable of transferring light energy from their peripheral OXD arms to their emitting acceptors, where the chromophore luminance induced by energy transfer is more efficient than that by direct excitation of the emitting cores. In compared with acceptor emitters, not only can the emission wavelength be tuned (up to 100 nm of red-shift) by H-bonds, but also much higher emission efficiencies of the H-bonded complexes were induced by reduced aggregation and energy transfer from the OXD donor dendrons.