雙噻吩基苯并雙噻吩為主體之新型階梯狀七環融合結構:合成與性質鑑定並於有機光電元件之應用

Abstract

我們設計且合成出一系列以雙噻吩基苯并雙噻吩(dithienylbenzodithiophene)為主體之新穎七環融合階梯狀結構BDCPDT(benzodicyclopentadithiophene)和TBDT(terbenzodithiophene)。BDCPDT是以碳原子為共價橋樑連接中心苯并雙噻吩(benzo[1,2-b:4,5-b′]dithiophenes)之3號和7號位置與外圍噻吩的3號位置，我們利用酸性催化條件之Friedel-Crafts 反應進行環化，形成兩個雙噻吩環戊二烯（cyclopentadithiophene，CPDT）與中心苯并雙噻吩共享兩個噻吩之結構。選用單體BDCPDT並與三種不同電子受體thienopyrroledione (TPD) 、benzothiadiazole (BT) 與difluorobenzothiadiazole (FBT)共聚，依序得到PBDCPDT-TPD、PBDCPDT-BT與 PBDCPDT-FBT。將三種高分子進行光學與電學等性質鑑定後並製成正結構有機高分子太陽能電池元件(ITO/PEDOT:PSS/polymer:PC71CM/Ca/Al)，初步得到的光電轉換效率分別為5.2 %, 4.8 % 與5.6 %。嘗試將高分子PBDCPDT-TPD元件結果最佳化，選用極性溶劑二甲基亞碸(DMSO)做為添加劑可將效率提升至6.1 %，若是再將電洞傳輸層材料poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)改由氧化鉬(MoO3)取代，其效率可達6.6 %。此外，高分子PBDCPDT–FBT擁有高的電洞遷徙率與和poly(3-hexylthiophene)(P3HT)吸收互補之特性，被選用當作層疊式太陽能電池之材料，其元件得到了超高的開路電壓值1.62 V，光電轉換效率更是達到了7.08 %。 另一部分，我們利用雙噻吩基苯并雙噻吩為主體，合成出另一個平面性更佳之七環融合階梯狀結構TBDT，以乙烯基為共價橋梁連結中心苯并雙噻吩與外圍噻吩分子並藉由控制外圍噻吩分子之連結位置，得到syn-TBDT與anti-TBDT兩種異構物。我們利用不同的合成策略，可以在TBDT之共軛結構上導入不同數目之長碳鏈取代基能得到雙取代正癸烷基之TBDT(didecyl TBDT，DDTBDT)或是四取代正癸烷基之TBDT(tetradecyl TBDT，TDTBDT)。在鹼性條件下，經由1,8-diazabicycloundec-7-ene (DBU)催化進行分子內6-電子環化反應分別可得到四種DDTBDT之異構物(syn-6, 13-TBDT、syn-6, 13-TBDT、anti-6, 13-TBDT和anti-7, 14-TBDT)。四取代正癸烷基TBDT則是選用雙噻吩基苯并雙噻吩之雙碘前驅物經由鈀金屬催化與雙取代長碳鏈炔或雙取代噻吩基炔進行反應，經由碳氫鍵芳香環化可分別得到syn-TDTBDT、anti-TDTBDT和 syn-TTTBDT。所有得到之新穎七環融合結構分子皆經過結構鑑定及性質測定，並對其基本性質進一步分析及探討。在此選用平面性佳且擁有良好溶解度的單體syn-TDTBDT與dithienyldiketopyrrolopyrrole (DPP)、isoindigo(IID)和bithiophene (TT)經由鈀金屬催化進行Stille 反應聚合後，分別得到PsTDTBDT-DPP、PsTDTBDT-IID和PsTDTBDT-TT。經由光學及電學性質測定，將三個共聚高分子製成下閘極底接觸之有機場效應電晶體，初步結果得到之電荷遷徙率分別為0.14、0.001和0.03 cm2 V-1s-1。除此之外，選用具有二維共軛結構之單體syn-TTTBDT與fluorothienothiophene (FTT) 和difluorobenzothiadiazole (FBT)共聚後分別得到PsTTTBDT-FTT和PsTTTBDT-FBT，兩個共聚高分子皆擁有較低的HOMO能階分別為－5.84和－5.80 eV，在製成反結構高分子太陽能電池元件(ITO/ZnO/polymer: PC71CM/MoO3/Ag)時，反映至開路電壓上得到0.94 V與0.90 V，當加入適當的添加劑之後初步得到的效率值為3.98 %與3.83 %。未來將使TBDT系列小分子應用至有機場效應電晶體中，進一步探討其效率值之差異並優化TBDT共軛高分子光電元件之表現。

We have developed a series of new ladder-type dithenylbenzodithiophene based heptacyclic arenes, benzodi(cyclopentadithiophene) (BDCPDT) and terbenzodithiophene (TBDT). We utilized the acid-induced Friedel-Crafts cyclization to construct the structure of BDCPDT, where 3,7-positions of the central benzo[1,2-b:4,5-b′]dithiophenes (BDT) subunit are covalently rigidified with 3-positons of the two external thiophenes by two carbon bridges, forming two external CPDT rings that share two thiophene rings with the central BDT core. BDCPDT monomer was polymerized with 1,3-dibromo-thieno[3,4-c]pyrrole-4,6-dione (TPD), 4,7-dibromo-2,1,3-benzothiadiazole (BT) and 4,7-diiodo-5,6-difluoro-2,1,3-benzothiadizole (FBT) to afford three copolymers PBDCPDT-TPD, PBDCPDT-BT and PBDCPDT-FBT. After characterization of these three copolymers, the conventional devices (ITO/PEDOT:PSS/polymer:PC71CM/Ca/Al) were fabricated for the polymer solar cells application and the preliminary performance were 5.2 %, 4.8 % and 5.6 %, respectively. Under the optimal device conditions using DMSO as the additive and MoO3 as the hole-selective layer, the device using PBDCPDT-TPD:PC71BM (1:3 in wt %) delivered a marked PCE of 6.6%. Furthermore, PBDCPDT-FBT, with high hole mobility and more red shift absorption spectrum than P3HT, was selected to fabricate the tandem solar cells exhibiting a Voc of 1.62 V and a PCE of 7.08%. On the other hand, based on the dithienylbenzodithiophene skeleton, we have designed another more planar ladder-type terbenzodithiophene (TBDT) structure where the BDT unit is fastened with two outer thiophenes by sp2–sp2ethylene bridges. By controlling the fused position of the outer thiophene with the central BDT core, the isomeric syn-TBDT and anti-TBDT molecules can be obtained. We employed different synthetic strategies to successfully introduce two alkyl and four alkyl chains on the conjugated backbone of TBDT, leading to didecyl TBDT (DDTBDT) and tetradecyl TBDT (TDTBDT), respectively. Four isomeric structures of DDTBDT (denoted as syn-6, 13-TBDT、syn-7, 14-TBDT、anti-6, 13-TBDT and anti-7, 14-TBDT) are prepared by the base-induced intramolecular 6-cyclization of the precursors in the presence of diazabicycloundecene (DBU). Furthermore, TDTBDT (denoted as syn-TDTBDT、anti-TDTBDT and syn-TTTBDT) units were constructed by the palladium-catalyzed reaction of a diiodo-dithienylbenzodithiophene-based molecule with didodecylacetylene or dithienylacetylene moieties via a C-H arylation mechanism. All the newly designed ladder-type structures have been carefully characterized and systematically analyzed. The monomer syn-TDTBDT was chosen to polymerize with dibromodithienyl-pyrrolo[3,4-c]pyrroledione (DPP), dibromoisoindigo (IID) and dibromo-2,2'-bithiophene (TT) by Stille coupling to afford three copolymers PsTDTBDT-DPP、PsTDTBDT-IID and PsTDTBDT-TT. Base on the bottom-gate bottom-contact OFET devices, the hole mobility are 0.14, 0.001 and 0.03 cm2 V-1s-1, respectively. Additionally, the syn-TTTBDT monomer was polymerized with 4,6-dibromo-3-fluorothienothiophene (FTT) and 4,7-bis(5-bromo-thienyl)-difluorobenzothiadiazole (FBT) to afford two copolymers PsTTTBDT-FTT and PsTTTBDT-FBT, that exhibited much lower HOMO energy level of －5.84 and －5.80 eV, respectively. After introducing diphenyl ether (DPE) and diphenyl sulfide (DPS) as the additives in the inverted polymer solar cells device (ITO/ZnO/polymer: PC71CM/MoO3/Ag), the preliminary power conversion efficiency were 3.98 % (PsTTTBDT-FTT) and 3.83 % (PsTTTBDT-FBT) with very high Voc of 0.94 V and 0.90 V, respectively. The applications of the TBDT-based small molecules in the OFET devices are currently ongoing in our laboratory. The optoelectronic performance of TBDT-based polymers will be also optimized in the near future.