雙苯環取代之聚(1,4-仲苯基乙烯)之合成及其在發光二極體之應用

Abstract

本研究主要目的係合成poly(2,3-diphenyl-5-n-hexyl-p-phenylene vinylene) ( DP6-PPV, 以下簡稱1P )及poly(2,3-diphenyl-5-(2-(1,4,5- triphenyl-1H-2-imidazoloyl)-1-oxytrimethylene phenyl)phenylene vinylene) ( DPTI-PPV, 以下簡稱2P ) 兩個可溶性的PPV系列聚合物，除了基本的結構鑑定外，亦探討其熱性質與光學性質，此外，本研究亦製作單層及雙層之高分子有機發光二極體元件，研究所合成聚合物之電激發光性質。 聚合物1P及2P均採用Gilch路徑的聚合方式，在鹼性的條件下聚合而成，兩種聚合物皆可溶於氯仿及四氫口夫喃等有機溶劑。聚合物1P的玻璃轉移溫度為131.9oC，熱分解溫度為427.5oC，其數目平均分子量為12840，重量平均分子量為34490，分子量分佈為2.68。聚合物2P的玻璃轉移溫度為 146oC，熱分解溫度為394oC，其數目平均分子量為143800，重量平均分子量為418200，分子量分佈為2.91。兩個聚合物均具有相當高的熱穩定性，且分子量分佈皆控制在3以內。 在光學性質方面，聚合物1P薄膜的UV-Vis最大吸收及PL最大放射波長別在366 nm及486 nm，聚合物2P薄膜的UV-Vis最大吸收及PL最大放射波長分別在375.4 nm及482.6 nm，兩者皆具有綠色的螢光。 經循環電位伏安法( CV )測試，可估算出聚合物1P的HOMO為5.55eV，而LUMO為2.7 eV，聚合物2P的HOMO為5.51 eV，而LUMO為2.62 eV，能帶大小的不同主要是由於聚合物2P在側鏈所連接的imidazole 基團所導致。 將聚合物製作成單層元件ITO/polymer/Al，可分別得到其電激發光，以聚合物1P作為發光層時，在13V可開始驅動而發光，其EL的最大放射波長為488 nm，CIE座標為( 0.237, 0.447 )，而以聚合物2P作為發光層時，在17V時開始驅動而發光，其EL的最大放射波長為487nm，CIE座標為( 0.219, 0.474 )，以IV及BV圖譜可看出以聚合物1P作為發光層的元件會較聚合物2P有更低的驅動電壓及發光效率，這主要是由於聚合物1P的LUMO能階較聚合物2P的LUMO能階為大，因此較有利於電子的注入與傳輸。而將聚合物製作成雙層元件ITO/PEDOT/polymer/Al，加入一層PEDOT作為電洞傳輸層，以聚合物1P作為發光層時，驅動電壓由單層結構時的13V降低為5V，而以聚合物2P作為發光層時，驅動電壓由單層結構時的17V降低為7V。

The goal of this study is to synthesize two soluble poly(phenylene vinylene) (PPV) based polymers, i.e., poly(2,3-diphenyl-5-n-hexyl-p- phenylene vinylene) (DP6-PPV, 1P) and poly(2,3-diphenyl-5-(2-(1, 4, 5- triphenyl-1H- 2- imidazoloyl)- 1- oxytrimethylene phenyl) phenylene vinylene) (DPTI-PPV, 2P). The thermal and optical properties of both polymers were measured. Both polymers were used to fabricate the single and double layer light-emitting devices. The electroluminescent properties of the devices were studied. Both polymers 1P and 2P were synthesized according to the Gilch route in basic conditions. The synthesized polymers are soluble in common organic solvents, such as chloroform and THF. The number average molecular weights of 1P and 2P are 12840 and 143800 respectively. Their polydispersities are lower than 3. Polymer 1P shows a glass transition at 131.9oC while polymer 2P presents a glass transition at 146oC. Both polymers 1P and 2P exhibit very high thermal stability. Their thermal degration temperatures measured at 5% weight loss are 427.5oC and 394oC respectively. The UV absorption peaks of polymer 1P and 2P are 366 and 375.4 nm respectively. Their PL emission peaks are 486 and 482.6 nm. Both polymers emit green photoluminescence. The band gaps of polymers 1P and 2P are 2.85 and 2.89 eV respectively. Their difference is due to the bulky imidazole side group. The turn-on voltages of the single layer devices, ITO/polymer/Al, are 13 and 17 volt for polymers 1P and 2P respectively. Their maxima of EL emission are 488 nm for polymer 1P and 487 for polymer 2P. The polymer 1P shows a lower turn-on voltage in both I-V and B-V curves. The reason could be due to the higher electron injection. The turn on voltages of the double-layer devices, ITO/PEDOT/polymer/Al decreased dramatically because PEDOT is a good hole-transporting layer.