聯三伸苯衍生物之分子堆疊與光學性質間的相關性之研究

Correlation between Morphologies and Optical Properties of Triphenylene-derivative

余建源(Jian-Yuan Yu)

指導教授 ： 鄭建鴻 ； 陳俊顯

國立清華大學/理學院/化學系/博士(2009年)

摘要

一般而言，多共軛且平面的分子易形成結晶，不利於organic light-emitting diodes (OLEDs)材料上的應用。而2,2’-bistriphenylenyl (BTP)、1,4-di(triphenylen-2-yl)benzene (T1)及4,4’-di(triphenylen-2-yl)biphenyl (T2)這三個TP衍生物都是沒有取代基的多苯環、共平面分子，從X-ray單晶繞射的結果看出BTP和T1都是共平面結構，顯示此類分子容易形成結晶相，但從元件的製成結果看來三者都是優異的藍色螢光分子。透過原子力顯微鏡(atomic force microscopy, AFM)、理論計算及光激放光 (photoluminescence，PL)、電激放光(electroluminescence，EL)光譜的研究，瞭解分子堆疊及薄膜形態與光學性質間的相關性，發現這三個分子在蒸鍍成膜後會因為分子的聚集，使得元件放光波長會在藍光區域。也因為分子本身的立體障礙，減弱分子間的 作用力，因此可以抑制自淬熄(self-quenching)或自吸收(self-absorption) 等消光現象產生，使得這三個分子作為OLEDs的放光層都讓元件有好的效能。
比較BTP、T1和T2三者的化學結構，在T1及T2中，兩個發射團以phenylene及biphenylene作為架橋基，並提供立體障礙的來源，抑制分子的緊密堆疊。我們從AFM及PL、EL光譜證實如此的分子設計概念得以有效控制放光層薄膜更趨於均相的形態，抑制元件中非放光(radiationless)機制的產生，對於OLED元件的效能有更進一步的提昇。

關鍵字

原子力顯微鏡 ； 藍色螢光材料 ； 有機發光二機體

並列摘要

It is generally believed conjugated and planar molecules that are appropriate for light-emitting diodes (OLEDs) application due to strong intermolecular  stacking and induce self-absorption. The triphenylene (TP)-derivatives, 2,2’-bistriphenylenyl (BTP), 1,4-di(triphenylen-2-yl)benzene (T1) and 4,4’-di(triphenylen-2-yl)biphenyl (T2), are all sp2-hybridized polyaromatic compounds without derivatization. Also, X-ray crystallographic results of BTP and T1 crystals show the chemical structure are coplanar, indicative of a likely tendency toward self-quenching. Surprisingly, The device layouts prove the three compounds are excellent blue emitters. To correlate, AFM, theoretical calculation, and luminescence spectra are used to study the correlation between optical properties and the film morphology. AFM reveals grainy nanoaggregates of the emitting layer in the device based on the three TP-derivatives as emitters. The molecular aggregation makes ensembles of the emitters luminesce deep blue light. The small torsion barrier to rotate the TP rings suggest that these compounds adopt a range of dihedral angles which confer steric hinderance on molecular packing. Therefore, self-quenching and self-absorption are obstructed in the OLED device.
Comparing BTP, T1, and T2-nased devices, the EQE increases with the number of phenylene inserted between two TP-rings. The wavelengths of the EL for T1 and T2 appear no red-shift from that of BTP, suggesting that phenylene and biphenylene effectively reduce the intermolecular  stacking and do not increase the conjugation length of the biaryls in the devices. The effect of the inserted phenylene-moiety on the enhancement of film amorphism and the luminescence efficiency for small molecules is verified.

並列關鍵字

Atomic force microscopy ； Blue-light emitters ； Bistriphenylenyl ； Organic light-emitting diodes ； Phenylene-substituents

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