合成含芴衍生物之超分枝聚合物與合成含芴之新穎發光材料及其光電性質之研究與應用

Abstract

本研究分為兩部分，第一部分主要利用超枝化聚合法(Hyperbranch Polymerization)合成得到超分枝高分子聚合物，探討特殊結構對其熱穩定性及發光特性的影響。採用氯化鉭(TaCl5) 催化的超枝化聚合反應，單體設計簡單，且配合適當濃度之催化劑及單一溶劑，即可聚合。所有的高分子則透過傅立葉紅外光光譜儀、凝膠滲透層析儀、熱重分析儀、微差掃描卡計、螢光光譜儀及電激發光實驗作為其定性上的分析。 本系列高分子單體採用常見之藍、綠、紅光材料，藉以探討高分子特殊網狀結構對於發光及其他光電性質；此外也拿紅光材料應用於有機太陽能電池之中，其最佳轉換太陽能效率為0.29%。在熱性質方面因為特殊枝網狀結構，所以其Tg皆可達到50oC以上，而hb-TF具有最高的Tg值，推斷是 hb-TF的結構較剛硬。而hb-BTF因為結構愈不平整的緣故，呈現出較低的Tg值；但hb-BTDTF因有thiophene分子的導入，使Tg較hb-BTF高。在光學性質方面，hb-BTF與hb-BTDTF在UV-vis吸收光譜中有兩個吸收峰，但在PL光譜中，只有一放射峰，推測在分子內能量傳遞良好。 元件部分採用ITO/PEDOT/Polymer/CsF/Al (單層元件)。在電激發光的光色表現上，hb-TF因堆疊較為嚴重，光色為藍偏綠色，元件效率最大亮度在12V為50 cd/m2，EL最大在520 nm與單一芴單體超分枝聚合物一致，hb-BTF最大亮度在13V為42 cd/m2；EL約在綠光位置 hb-BTDTF最大亮度在9V為29 cd/m2， EL約在紅光位置。

本研究第二部分主要目的在於以Anthracene與fluorene共聚的新穎共軛高分子及其在高分子電激發光二極體之應用。成功以Sonogashira 耦合法可合成出高分子量之聚合物(MW>220,000)，合成出來的高分子熱穩定性佳，其熱裂解溫度高於390 oC，而玻璃轉移溫度則約在50 oC，並且對一般常用的溶劑，如THF及Toluene皆有不錯的溶解度，有利於使用旋轉塗佈法在元件的製作。這些高分子在光學性質部分，其溶液態與薄膜態之螢光光譜的主峰相差有約80nm，為藍色偏綠，推測有嚴重之堆疊情況發生，應為共聚之ter-fluorene增加π-πstacking之緣故。 在元件的表現上，F3-T在7 V達最大亮度100 cd/m2，最大效率為0.02 cd/A。

This study is focused on the synthesis of hyperbranched fluorene derivatives and their applications in polymer light-emitting diodes (PLEDs) and solar cells. Three polymers, hb-TF, hb-BTF and hb-BTDTF, were synthesized by [2+2+2] trimerization of the corresponding oligo-arene diacetylene monomers using TaCl5 as the catalyst. All the polymers were fully characterized by Fourier transform infrared spectrometer (FT-IR), gel permeation chromatography (GPC), thermal gravimetric analyzer (TGA), differential scanning calorimeter (DSC), photoluminescence spectrophotometer (PL), and electroluminescent (EL) spectroscopy. The effect of the hyperbranched structure on the thermal and luminescent properties is discussed. All the synthesized polymers showed good thermal stability (Td > 380 oC) with glass transition temperatures higher than 50 oC. The hb-TF polymer has the highest Tg due to it more rigid structure. When the central fluorene is replaced by a benzothiodiazole group, the Tg of hb-BTF decreased. However, the Tg of hb-BTDTF increased again when two additional thiophene groups are introduced. hb-BTF and hb-BTDTF exhibit two peaks in the UV-vis spectra but only one peak with lower energy in the PL spectra, implying that the energy transfer occurs efficiently in these polymers. Single-layer devices were fabricated by using the device configuration of ITO/PEDOT/Polymer/CsF/Al. The electroluminescence of device based on hb-TF showed a bluefish-green light with a maximum brightness of 50 cd/m2 at 12V. hb-BTF-based device emits a green light with a maximum brightness of 42 cd/m2 at 13V and hb-TF-based device displayed a red emission with a maximum brightness of 29 cd/m2 at 9V. On the other hand, a bulk heterojunction solar cell device was fabricated using the composite of hb-BTDTF and PCBM (1:2 in wt%) as the active layer, showing a power conversion efficiency of 0.29%.

We also synthesized a polymer F3-T with high molecular weight (MW > 220,000) by using Sonogashira coupling of ter-fluorene monomer M1 and anthracene monomer M4. This polymer showed good thermal stability (Td > 390 oC) and the glass transition temperature is higher than 50 oC. The polymer has good solubility in common organic solvents, such as toluene or THF, which facilitates the solution processing of devices. Due to theπ-πstacking aggregation, the polymer F3-T exhibited a maximum emission at 508 nm in solid state, which is about 80 nm red-shifted as compared to 426 nm in the solution state. Based on the device ITO/PEDOT/F3-T/CsF/Al configuration, the maximum brightness was 100 cd/m2 at 7 V, and maximum luminance efficiency was 0.02 cd/A.