含雙氰基吡啶材料之設計、合成與性質及其在熱激活化延遲螢光有機發光二極體之應用

Design, Syntheses and Properties of Dicyanopyridine-Based Materials for Thermally Activated Delayed Fluorescence in Organic Light Emitting Diodes

彭子軒(Tzu-Hsuan Peng)

指導教授 ： 汪根欉

國立臺灣大學/理學院/化學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201803912

摘要

本論文目標設計出具有熱激活化延遲螢光 (TADF) 性質的有機分子，且螢光在橘紅色光範圍。其分子必須具備非常小的單重激發態最低能階與三重激發態最低能階之間的能隙 (ΔEST)，使得三重激發態的激子 (exciton) 能夠透過環境熱能的幫助，發生自旋轉換以進行反向系統間跨越 (RISC) 接著放出延遲螢光，預期內部量子效率 (IQE) 接近100%。
本研究主要合成出四個以5,6-雙氰基吡啶 (Py56)為電子受體的雙極性分子，第一部分藉由改變電子予體的推電子能力，將9,10-二氫-9,9-二甲基吖啶 (DMAC) 置換成吩噻嗪 (PTZ)，使PTZ分子的放光波長有效紅移約90nm。由固態薄膜量測確實具有很小的ΔEST與TADF性質。其中8 wt% 的混摻薄膜量子產率為50.6%、ΔEST為81.2 meV，製作成元件後最大外部量子效率為12.4%，放光波長為620 nm；在20 wt% 的元件中波長最長為644 nm且最大外部量子子效率為8.9%。
第二部分將原有電子予體向外再延伸不同的推電子基團，使分子的最高佔有軌域提升造成光色紅移，其中AcAcAc與tNActN比起Ac分別紅移了14 nm及68 nm；同時藉由擴展電子予體，使其最高佔有軌域在空間上的分佈向外延伸，進而降低分子中最高佔有軌域 (HOMO)、最低未佔有軌域 (LUMO) 的重疊積分，達到降低 ΔEST 的目的。此系列三個分子CzAcCz、AcAcAc、tNActN確實藉由延伸donor基團達到光色紅移且同時降低ΔEST的效果，但因分子量過大且結構為較為鬆散，因此無法昇華純化製作後續固態薄膜與元件。不過這系列分子因為延伸donor使得整體分子為D’-π-D-π-A的結構，在溶液態下可以觀察到兩個同時存在的CT state，分別為TBCT及TSCT，前者放光較藍而後者偏橘黃，藉由調控溶劑極性與激發波長即可變動兩個放光波長以及訊號強度，在某些情況下可以觀察到很特別的單分子白光。

關鍵字

熱激活化延遲螢光 ； 有機發光二極體 ； 紅光 ； 發光材料

並列摘要

Thermally activated delayed fluorescent OLEDs (TADF OLEDs), possessing equally high emitting ability that reach near 100% internal quantum efficiency and similar device configuration in comparison with PhOLEDs. Using pure aromatic compounds with small singlet-triplet energy gap (∆EST), which enable triplet excitons to up-convert into emissive singlet excitons through effective reverse intersystem crossing (RISC), as emitters exempts the dependence on noble metals.
In this report, we design and synthesis four TADF molecules which emit orange to red fluorescence with dicyanopyridine as the acceptor group. The first part is directly changing donor from DMAC to PTZ. The stronger electron donating ability result in red-shift about 90 nm. Small ∆EST and obvious TADF character are found in PTZ. In 8 wt% doped film, the PLQY is 50.6% and the ΔEST is 81.2 meV, and the device demonstrates a relatively high external quantum efficiency of 12.4% with wavelength at 620 nm. The devive with the longest wavelength is for 20 wt% doping concentration, with EQE 8.9% and wavelength at 644 nm.
Second part is about extending DMAC with three donor group: Cz, Ac and tN. AcAcAc and tNActN are red-shifted 14 nm and 68 nm in comparison with Ac. Extending the donor group not only raises HOMO in order to reduce energy gap, but also extends the distribution of HOMO that makes ∆EST smaller. The structure of these compounds belongs to D’-π-D-π-A, leading to two CT states that we called TBCT and TSCT. The former emits sky-blue and the latter is orange-yellow light. We can control these two TADF emissions by changing solvent or excitation wavelength. It is really interesting that in some conditions, we can observe white light emission with just a single molecule.

並列關鍵字

OLED ； TADF ； Thermally Activated Delayed Fluorescence ； Organic Light Emitting Diodes

參考文獻

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