運用官能化樹枝狀及高分枝狀結構之非聚集途徑以提昇高分子發光二極體之性能

Abstract

一系列不同代數包含圻堮雙唑(oxadiazole)（OXD）雜環之樹枝狀化合物已被合成與鑑定，當不同代數樹枝狀OXD基團懸掛於包含聚茀共軛高分子側鏈上時，這些高分子具有極佳的溶解度與熱性質，並可有效的抑制結晶性與高分子鏈聚集的現象，進而有效提高螢光效率，且避免光色不純的現象產生。此外，當激發側鏈OXD基團時，可發生能量轉移到高分子主鏈上。特別的是，在連接高代數的樹枝狀OXD的高分子時，激發外部OXD基團，其螢光效率更大於直接激發共軛高分子。當作成元件時，連接高代數的樹枝狀OXD的高分子呈現穩定的藍光波長，其光電特性優於傳統聚茀高分子。再者，將一系列不同代數包含圻堮雙唑(OXD)雜環的樹枝狀化合物結構的焦點設計成酸基團時，可與具單吡啶雜環與雙吡啶雜環的發光質子受體形成氫鍵錯合物，這些包含圻堮雙唑(OXD)雜環的氫鍵錯合物可有效防止發光分子聚集，進而提高螢光效率，同時不同代數的氫鍵錯合物可發不同的波長的光色。當激發氫鍵錯合物的OXD基團時，可發生有效能量轉移到包含單吡啶雜環與雙吡啶雜環的發光質子受體上，同樣地，在高代數的氫鍵錯合物，激發氫鍵錯合物的OXD基團，其螢光效率更大於直接激發單吡啶雜環與雙吡啶雜環的發光質子受體。 另外，在使高分子形成高分枝結構之研究上、利用不同含量與不同官能基數目之carbazole(CAZ)單體與茀（fluorene）單體進行聚合，可得一系列高分枝狀高分子，能使聚茀共軛高分子（Poly(fluorene)）產生不同之分枝程度結構，這樣方式有效改善分子間聚集之現象並且維持高分子主鏈良好共軛程度，使得產生之高分子具良好的螢光效率。

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.