新穎藍光含蒽共軛高分子之合成及其在高分子電激發光二極體之應用

Abstract

本研究的主要目的在於合成以Anthracene為基礎的共軛高分子及其在高分子電激發光二極體之應用。我們成功合成出六個以9,10-Bis(6-bromonaphthalen-2-yl)-2-tert-butylanthracene (TBADN)與Fluorene衍生物混掺的藍光高分子。所有共聚物除了TAZ-T50是以Yamamoto polymerization做聚合外，其他的高分子如F-T50、DPF-T5 ~ DPF-T50及TAZ5-DPF-T45皆是以Suzuki polymerization作為合成方法。 第一部分將TBADN與具有長碳鏈的Fluorene(PFO)進行聚合反應得到F-T50，希望藉由長碳鏈的導入能有效改善TBADN同聚物(homopolymer)溶解度不佳的問題。至於第二部分，為了解決一般高分子材料於薄膜態易有共軛主鏈因π-πstacking造成堆疊現象發生而產生消光的情形，我們利用苯環衍生物的加入，企圖增加芴分子於九號碳位上取代基的立體障礙，來減少高分子共軛主鏈的堆疊，故合成出DPF-T系列高分子，其中透過調整TBADN與Fluorene衍生物的比例，希望高分子主鏈將所吸收到的能量以較有效的方式如Host-dopant的能量轉移機制來提升材料發光的效率。另外聚芴高分子本質上是以傳輸電洞為主的材料，故在第三部分，藉由在高分子的側鏈導入具有傳導電子能力的官能基如1,2,3-三氮唑(1,2,3-triazole units)，可以增加正負電荷於發光層中再結合的比例，使其因電子電洞平衡而提升元件效率，所以合成出TAZ-T50與TAZ5-DPF-T45。所有合成出來的高分子熱穩定性佳，其熱裂解溫度高於330 oC，而玻璃轉移溫度則高於80 oC，並且對一般常用的溶劑，如THF及Toluene皆有不錯的溶解度，有利於使用旋轉塗佈法在元件的製作。這些高分子在光學性質部分，其溶液態與薄膜態之螢光光譜的主峰都在約440 nm ~ 460 nm的藍光範圍，而且具有不錯的螢光量子效率 (Φsol=61~88 %，Φfilm=14~26 % )。在電化學的量測部份，HOMO值約在-5.8 ~ -5.9 eV，而LUMO值約在-2.9 ~ -3 eV，大致上來說，我們所合成出來的高分子其LUMO值較低，有利於元件上電子從陰極端注入至發光層。 元件製作部分主要是以ITO/PEDOT:PSS/Polymer/CsF/Al的形式做雙層的元件結構，其中最佳的材料為DPF-T50。在驅動電壓為13V下可達最大亮度1650 cd/m2，此時CIE 色度座標值為(0.22,0.33)，光色為藍綠光，而最大發光效率則為0.39 cd/A。綜合上述雙層元件結果來看，我們所合成出來的含蒽聚芴高分子，具有不錯的發光效率(luminance efficiency，LE)，而且在高操作電壓下也有不錯的穩定性。

This study focused on the synthesis of anthracene-based copolymers and their applications in polymer light-emitting diodes (PLEDs). We had synthesized six copolymers, i.e., F-T50, DPF-T5, DPF-T25, DPF-T50, TAZ5-DPF-T45 and TAZ-T50, containing 9,10-Bis (6-bromonaph thalen-2-yl)-2-tert-butylanthracene (TBADN) and 2,7-disubstituted fluorene moieties. All of these copolymers were synthesized via palladium-catalyzed Suzuki polymerization except TAZ-T50 which was synthesized by nickel-mediated Yamamoto polymerization. The first polymer F-T50 were prepared by Suzuki coupling of TBADN with boronic ester of fluorene derivative which contains long alkyl chains in the C-9 position of fluorene units for improving the solubility of the obtained polymer. However, the PLED device performance of F-T50 was quite low. We introduced a bulky phenyl-ring in the C-9 position of fluorene units so as to reduce the aggregation caused by π-π interaction between polymer main chains in the other polymers DPF-T5~DPF-T50. We tuned the mole ratio between TBADN and fluorene derivatives among these polymers as to enhance the luminance efficiency through Förster energy transfer. Finally, we synthesized both TAZ5-DPF-T45 and TAZ-T50 polymers which contained electron transporting 1,2,3-triazole units on the C-9 position of a fluorene ring. All the synthesized polymers showed good thermal stability ( Td > 330 oC ) and their glass transition temperature is higher than 80 oC. The synthesized polymers emit blue light in the region from 440 nm to 460 nm in both solution and thin film states. Their HOMO and LUMO energy levels are in the range from -5.8 to -5.9 eV and -2.9 to -3.0 eV respectively. These results demonstrate that electrons could inject from cathode to polymer emitting layer easily. All of these polymers had good solubility in common organic solvent, such as toluene or THF. A double layer PLED device with the configuration of ITO/PEDOT:PSS/Polymer/ CsF/Al was fabricated. The EL spectra exhibited simalr emissions with those of PL spectra. The best EL device was achieved by using DPF-T50 as an emitting layer. Its maximum brightness was 1650 cd/m2 at 13 V, and maximum luminance efficiency was 0.39 cd/A. The CIE coordinates was (0.22, 0.33) at 13V. It means that this device emits a greenish-blue color.