"1,1-二苯基乙烯引入咔唑及苯并咪唑之合成、性質探討與其在有機發光二極體及質子偵測之應用"

Abstract

延續本實驗室陳孟欣學姊的研究，合成以四苯基乙烯為主體，鄰位接有咔唑及三咔唑作為推電子基的聚集誘導放光 (Aggregation induced emission, AIE) 分子，與推電子基位於間位及對位的化合物做比較，觀察推電子基位置對光色的影響。其中有三咔唑的化合物可以在ITO玻璃表面發生電聚合反應，薄膜顏色會隨外加電位不同而改變，是電致變色的薄膜。 而後改以1,1-二苯基乙烯為主體，在碳=碳雙鍵上引入咔唑作為推電子基、苯并咪唑為拉電子基，藉碳=碳雙鍵上的碳原子達到阻斷共軛的效果，使光色為藍光，並提高其三重態能階。以此分子設計所合成之p-BzctPE，螢光強度隨水體積比提高而增強，且其固態量子產率高達100%，有明顯的AIE現象。另外，其螢光及磷光放射起始波長重疊，可能具單重激發態與三重激發態能量相近之特性，其螢光生命期為2.67 ns。 我們以p-BzctPE為客發光體，搭配有高三重態能量的o-DicbzBz為主發光體，以此主客系統的組合應用於有機發光二極體元件的發光材料，元件初燒結果其放光波長落在500 nm，在最大亮度為1 cd/m2時，啟動電壓約為3.5 V、最大亮度為3466 cd/m2，最大發光功率為10.2 lm/W、最大電流效率約11.4 cd/A、最大外部量子效率高達5.0%，已高達電激螢光元件的理論數值。 亦發現o-BzcDPE及p-BzcDPE具有質子偵測的功能，此兩分子的固態及溶液態以肉眼觀察為微弱、不易辨識的紫色螢光，一旦加入酸性溶液後，在短時間內會轉變為亮度明顯的綠色螢光，推測當質子作用在苯并咪唑的氮上，會造成咔唑和苯并咪唑發生共振，使光色紅移，且在低質子濃度的溶液中即可觀察到此現象，顯示對質子具有高靈敏度。此外，與過當量的NCS及BH4-反應，也會造成光色改變，反應機制及當量數仍需做更多調查，具開發作為螢光指示劑的潛力。

In my research, tetraphenylethylene is introduced as main unit, which is a kind of AIEgens and then carbazole and tricarbazole functional group are introduced at ortho position of tetraphenylethylene to compare their physical properties with the meta and para substituted molecules synthesized by Meng-Sin Chen. Particularly, the molecules with tricarbazole functional group can form stable electropolymer thin film on the surface of ITO glass with electrochromic effect. Then, we change the AIE structure by introducing carbozole as electron donating group and benzimidazole as electron withdrawing unit to the carbon-carbon double bond of 1,1-diphenylethylene which is the main group. The carbon atom can interrupt the π – conjugation to increase triplet energy and emit blue fluorescence. Accroding to the structure design, we obtain p-BzctPE with 100% solid quantum yield and the fluorescence intensity rises as water fraction become higher gradually showing that it has strong AIE effect. In addition, the wavelength of fluorescence and phosphorescence onset are similar indicating that p-BzctPE may has close singlet and triplet energy level. However, its fluorescence lifetime is different from the time scale of TADF materials, at 2.67 ns. There is excellent efficiency of energy transfer between o-DicbzBz and p-BzctPE, so we use these two materials as host and guest, respectively. The wavelength of OLED made by the doped emitter is at 500 nm, the turn-on voltage is 3.5 V, the maximum luminance is 3466 cd/m2, the maximum current efficiency is 11.4 cd/A, the maximum power efficiency is 10.2 lm/W, and the maximum external quantum efficiency reaches the theoretical value of electrofluorescence OLED, at about 5%. We also find that o-BzcDPE and p-BzcDPE display the outstanding ability of proton detection. Their fluorescence intensity are extremely weak in both solid and solution state. When acid solution is added into the solution of o-BzcDPE and p-BzcDPE, the fluorescence will be red shifted obviously in a short time. The reason may be that proton reacts with nitrogen atom of benzimidazole, then carbozole donates electron to stabilize the positive charge results in resonance between carbazole and benzimidazole and the red shifted spectrum. They have potential to be developed as fluorescent indicator.