有機發光二極體之芴與螺結雙芴螢光材料

Abstract

第二章：設計並合成出結合diphenylamino推電子性及dicyanovinyl拉電子性的稀有螢光芴衍生物。由pTSPDCV, 2-di(4-tolyl)amino-7-dicyanovinyl-9,9’- (2,2-biphenyl) fluorene和PhSPDCV (2-diphenylamino-7-dicyanovinyl-9,9’-(2,2’- biphenyl) fluorene)單晶x光繞射結構顯示於固態時，除了長距離分子偶極-偶極吸引力外只有微弱的凡得瓦力接觸力。引進龐大的9,9’-螺結雙芴取代和非共平面雙苯胺基一樣具有阻止偶極效應茀分子的聚集。比起色彩不鮮明的Nile Red and DCM (4-(dicyanomethylene)-2-methyl-6-[4-(dimethylaminostyryl)-4H-pyran]) 固體，此芴衍生物明顯具有更亮的螢光。這些與其他摻入物不同且獨特的光物理性質使得此類紅色芴衍生物更適合製成非摻入式紅光有機發光二極體。以pTSPDCV或PhSPDCV成功製作成非摻入式紅色有機發光二極體。此紅色電激發光(CIE, x = 0.65, y = 0.35)展現出最大亮度超過12000 cd/m2，於20 mA/cm2時具有超過600 cd/m2的高放光亮度，3.6%的最大外部量子效率更是值得注意。 第三章：我們發表一個新的有關合成純的2,2’-dibromo-9,9’-spirobifluorene方法，避免了容易出現副反應的9,9’-螺結雙芴直接雙溴化或是經由以2,2’-diamino-9,9’-spirobifluorene進行Sandmeyer反應。進一步合成一系列多個不同螢光化合物，化合物結構中具有一組推拉電子對兩兩互相垂直而不相交。我們選擇三組共六個螺結雙芴化合物作為研究對象，分別是紅色的PhSPDCV和其二聚分子BisPhSPDCV、綠色的PhSPCHO和其二聚分子BisPhSPCHO、藍色的PhSPDPV和其二聚分子BisPhSPDPV。此二聚螺結雙芴分子結構中含有一組兩個兩兩互相垂直而不相交的片段。我們預期分子中的兩片段相互的影響微弱，在製成有機發光二極體元件時兩個發光團應該會使元件效率加倍。然而對於紅色和綠色的發光團而言，二聚分子的分子偶極卻比單聚分子來的大。因此我們仔細的研究包含由理論計算的分子偶極、螢光的溶劑色移現象、螢光量子效率、單晶晶體結構和元件結果等物理性質。發現具有強偶極的PhSPDCV和PhSPCHO其相對的二聚分子BisPhSPDCV和BisPhSPCHO不論是元件效率或是螢光量子效率都比單聚分子差很多，但PhSPDPV和BisPhSPDPV的差別卻不大。因分子內或鄰近分子偶極所引起的區域電場會影響電激發光性質。特別是高極性BisPhSPDCV和BisPhSPCHO的螢光驟熄現象應該是由於其分子內的兩組推拉電子對各自所產生的能量轉移互相影響所產生的內部電場所引起的。因此為了避免電場所引起的螢光驟熄現象，分子的偶極需要有限度的控制。我們以0.5 wt% PhSPDCV製成摻入式發光元件，得到高效率（3.4%的外部量子效率、9.4 cd/A的發光效率、8.2 lm/W的電能效率）、高亮度（在20 mA/cm2的電流密度下約1800 cd/m2）的飽和黃色電激發光元件（1931 CIE 座標參數x = 0.50，x = 0.48）。此外， 以PhSPDPV製成非摻入式發光元件，得到高效率（3.4%的外部量子效率、5.4 cd/A的發光效率、5.7 lm/W的電能效率）、高亮度（在20 mA/cm2的電流密度下約910 cd/m2）的藍色電激發光元件(1931 CIE 座標參數x = 0.14，y = 0.22)。 第四章：設計合成PhSPDPV和PhSPN2DPV並研究其熱性質、光物理性質、電化學性質及電機發光元件性質。PhSPDPV和PhSPN2DPV兩者具有非常類似的玻璃轉移溫度(Tg約120 oC)和光物理性質。由單傳輸電洞和電子元件得知，PhSPN2DPV具有比PhSPDPV更佳的電子傳輸和注入能力。相對於PhSPDPV的電機放光元件，PhSPN2DPV具有較佳的電激放光元件效率(最大亮度為60500 cd/m2、最大外部量子效率為4.9%)。PhSPN2DPV的高元件效率是因為分子中的diaza官能基可以促進分子電子傳輸和電子注入能力，進而平衡元件中的電洞和電子，而增加電子電洞的再結合率。 第五章：設計並合成出一系列含有benzothiazole的雙苯胺基芴或螺結雙芴螢光體。利用在雙苯胺基的鄰位上引進甲基、氯、或是氟取代基可以輕易的改變螢光體的光色，將之藍位移由470 nm到439 nm。這些螢光體具有高達54 - 74 %的螢光放光效率，適合做為藍色電激發光的材料。以PhFBT摻入MADN中製成摻入式藍色電機放光元件，當摻入濃度為10 ~ 20%時，在20 mA/cm2的電流密度驅動下可達到4.7%的外部量子效率(摻入濃度為10%時)及高達28300cd/m2的亮度，相對應的最大放光波長位置在454-458 nm，CIE 座標參數x = 0.14-0.14，y = 0.13-0.15。有趣的是，此電激放光元件因為能量未能完全由主體MADN完全轉移到的摻入物PhFBT，而使得摻入物PhFBT和主體MADN共同放光。

Chapter 2: Rare red fluorescent fluorene derivatives were designed and synthesized. The long wavelength red fluorescence was achieved by incorporating di(4-tolyl)amino or diphenylamino electron donor and dicyanovinyl electron acceptor. Single crystal x-ray structure of pTSPDCV, 2-di(4-tolyl)amino-7-dicyanovinyl-9,9’- (2,2’-biphenyl) fluorene and PhSPDCV, 2-diphenylamino-7-dicyanovinyl-9,9’- (2,2’-biphenyl) fluorene indicates only weak non-□ van der Waals contact in addition to long distance dipole-dipole interaction of red fluorene molecules in solid state. The aggregation of the dipolar fluorene was largely suppressed by introducing bulky 9,9’-substituents (spiro-fused bifluorene) as well as the non-planar di(4-tolyl)amino or diphenylamino group. In solid state, these fluorenes derivatives all showed red fluorescence brightly compared with the dull red dopants of Nile Red and DCM (4-(dicyanomethylene)-2-methyl-6-[4- (dimethylaminostyryl)-4H-pyran]). The unique photophysical properties of red fluorene derivatives differ from other known red dopants and facilitate the fabrication of non-doped red organic light-emitting diodes (OLEDs). Authentic red (CIE, x = 0.65, y = 0.35) electro- luminescence with brightness over 12000 cd/m2 (or > 600 cd/m2 at 20 mA/cm2) and remarkable external quantum efficiency as high as 3.6% was observed for the red OLEDs with pTSPDCV or PhSPDCV as the sole host emitter. Chapter 3: Pure 2,2’-dibromo-9,9’-spirobifluorene was synthesized by a method that did not involve troublesome dibromination of 9,9’-spirobifluorene or Sandmeyer reaction of 2,2’-diamino-9,9’-spirobifluorene. A series of donor-acceptor orthogonally substituted 9,9’-spirobifluorene was subsequently prepared showing rich variation of fluorescence in solution and solid state. Here we study a series of strong fluorescence donor-acceptor-substituted spirobifluorene compounds, red PhSPDCV (2-diphenylamino-7-dicyanovinyl-9,9’-spirobifluorene), green PhSPCHO (2- diphenylamino-7-formyl-9,9’-spirobifluorene), and blue PhSPDPV (2-diphenylamino -7-diphenylvinyl-9,9’-spirobifluorene), together with their spiro “dimer” analogs, BisPhSPDCV (2,2’-diphenylamino-7,7’-dicyanovinyl-9,9’-spirobifluorene), green BisPhSPCHO (2,2’-diphenylamino-7,7’-diformyl-9,9’-spirobifluorene), and blue BisPhSPDPV (2,2’-diphenylamino-7,7’-diphenylvinyl-9,9’-spirobifluorene), respectively. The “dimeric” molecules are two identical units orthogonally linked in the spirobifluorene structure. The electronic interaction between the two molecular halves is expected to be weak, and thus the light-emitting density could be assembly doubled. However the dipole moments are also increased in the corresponding “dimeric” molecules in the red and green fluorophores. The physical properties including dipole moment from quantum chemistry calculation, emission solvatechromism, fluorescence quantum yield (□f), crystal packing X-ray structure, and OLED performance of these materials are examined and analyzed in details. We found that the fluorescence quantum yield as well as the OLED performance of the strongly dipolar red PhSPDCV and green PhSPCHO series decrease significantly in the “dimeric” structures (BisPhSPDCV and BisPhSOCHO), but not in the weakly dipolar BisPhSPDPV. The electroluminescence is closely correlated with the local electric field, which is induced by the dipole moments of nearby molecules or internal molecular halves. Particularly, the fluorescence quenching of highly polar “dimeric” BisPhSPDCV or BisPhSOCHO is likely due to the strong local electric field arising from the donor-acceptor functionalized molecular halves, with which a charge- transfer associated quenching channel may become feasible. To avoid electric field-induced fluorescence quenching, the molecular dipole moments should be limited. Within the context, dopant-based OLED containing 0.5% PhSPDCV light-emitter exhibited one of the most efficient (maximum external quantum efficiency of 3.4%, luminance efficiency of 9.4 cd/A, or power efficiency of 8.2 lm/W), bright (~1800 cd/m2 at 20 mA/cm2) saturated yellow (CIE, x = 0.50, y = 0.48) electroluminescence. On the other hand, non-dopant-based OLED containing PhSPDPV light-emitter exhibited very efficient (maximum external quantum efficiency of 3.4%, luminance efficiency of 5.4 cd/A, or power efficiency of 5.7 lm/W), bright (~910 cd/m2 at 20 mA/cm2) blue (1931 CIE, x = 0.14, y = 0.22) electroluminescence. Chapter 4: The synthesis, thermal, optical physical, electrochemical and electroluminescent properties of PhSPDPV and PhSPN2DPV were investigated. Both PhSPDPV and PhSPN2DPV exhibit similar high glass-transition temperatures (Tg ~112 oC) and similar optical physical properties either in solution or solid state. Hole- and electron-only devices of these two compounds were reported that PhSPN2DPV exhibit electron transporting and injecting ability better than PhSPDPV. Compared with PhSPDPV OLED, a significantly improved OLED performance was achieved for PhSPN2DPV (maximum brightness of 60500 cd/m2 and maximum □EXT of 4.9%). The diaza moiety improved the electron transporting and injecting ability of PhSPN2DPV and further enhanced the hole-electron charge recombination leading to more charge balance in PhSPN2DPV OLED. Chapter 5: A series of benzothiazole-carrying diarlyamino fluorene or spirobifluorene fluorophores were successfully prepared and investigated. By introducing methyl, chloro, or fluoro substituent to the ortho-position of diphenylamino donor, the fluorescence wavelength of chromophores can easily to blue-shited from 472 nm to 439 nm. These fluorene or spirobifluorene fluorophores show high fluorescent quantum yields in a range of 54-74% which are reasonably good for high efficiency blue OLEDs. High performance blue OLEDs containing PhFBT-doped MADN has been obtained with high dopant concentration of 10~20% with remarkable external quantum efficiency value of 4.7% (dopant concentration of 10 %) at the current density of 20 mA/cm2. The devices of the dopant concentration of 10~20% showed the emission □max at 454-458 nm corresponding to CIE coordinate, x = 0.14-0.14, y = 0.13-0.15 with highly brightness over than 28300 cd/m2. It is interesting that the blue EL emission is attributed to both PhFBT dopant and MADN host due to the incomplete Förster energy transfer or similar charge-trapping ability of the two materials.