以芴為主體所形成五與七環熔合梯型分子之合成、鑑定及其共軛高分子於有機太陽能電池與有機場效電晶體之應用

Abstract

我們成功地合成2,7-diiodo-3,6-dibromofluorene與2,7-dichloro-3,6-dibromofluorene這兩個重要的中間體，利用這兩個中間體對Sonogashira reaction有著不一樣的選擇性，進而合成2,7-DTF與3,6-DTF，這兩種位向異構物，依照相同的合成策略，我們可以合成出2,7-DSF與3,6-DSF。根據不同硫族 (硫與硒) 元素與同分異構物的影響，造成2,7-DTF、3,6-DTF、3,6-DSF和2,7-DSF在光學、電化學與熱性質展現出不同的差異。值得一提的是2,7-DTF與3,6-DTF和3,6-DSF的晶體結構展現出超分子自組裝螺旋結構。接著我們將新型電子予體 DTF與DPP (dithienodiketopyrrolopyrrole) 進行聚合反應，分別得到不同碳鏈的共軛高分子PDTFDPP16、PDTFDPP20和 PDTFDPP32。側鏈的修飾工程對於高分子的性質和高分子的排列皆占有重要的影響。根據理論計算PDTFDPP16的碳鏈不足所造成較差的溶解度，導致低的分子量。PDTFDPP16在2D-GIXS測量中呈現edge-on的排列；PDTFDPP20的碳鏈所造成立體阻礙與溶解度達到平衡，獲得高的分子量、適當的溶解度，在2D-GIXS測量中呈現face-on的排列；PDTFDPP32的碳鏈最長，雖然溶解度最佳，但立體阻礙的影響限制了聚合的進行，導致分子量介於中間。因為彎曲的構型，造成高分子的排列呈現非定性。我們將PDTFDPP20製作成有機場效電晶體元件，其結構為bottom-gate/top-contact，PDTFDPP20的電洞遷移率高達5 cm2 V−1 s−1且擁有高的電流開關比超過106。另一方面我們把2,7-bisthienylfluorene (BTF) 上的苯環與噻吩藉由架橋原子 (C=C雙鍵) 連接起來，也就是說擁有dieneyne的中間體在DBU的催化下進行兩次的分子內6π電子環化反應，形成擁有兩個分支碳鏈的新單體DTBF。接著我們將DTBF經由溴化後得到Br-DTBF分別與5,6-difluoro-4,7-bis(5-(trimethylstannyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (Sn-DTFBT) 和5,10-bis(5-(trimethylstannyl)thiophen-2-yl)naphtho[1,2-c:5,6-c']bis([1,2,5]thiadiazole) (Sn-DTNT) 進行聚合反應得到兩個共軛高分子PDTBFFBT與PDTBFNT。我們研究這兩個高分子材料的光學、電化學、高分子鏈彎曲率及分子堆疊、太陽能電池與有機電晶體的表現。經由GPC測量，PDTBFNT (Mn = 14.3 K g mol-1) 的分子量為PDTBFFBT的兩倍，而且PDTBFNT的光學能隙與電化學能隙皆小於PDTBFFBT。我們將這兩個高分子應用於反結構太陽能電池中 (ITO/ZnO/ polymer:PC71BM/MoO3/Ag)，加入5 vol %二苯醚做為添加劑時，PDTBFFBT:PC71BM與PDTBFNT:PC71BM的最佳之元件效率分別為2.68%與5.22%，PDTBFNT在短路電流的表現優於PDTBFFBT，除了PDTBFNT的LUMO能階與PC71BM的LUMO能階較為匹配外，我們也去測量2D-GIXS去探討高分子與碳球混摻後的排列結構，PDTBFNT展現了face-on的排列，此排列能增加電荷在垂直面上的傳遞，進而增加光電流。在有機場效電晶體的表現，PDTBFNT之最佳的電洞遷移率為1.90×10-2 cm2 V-1 s-1優於PDTBFFBT之最佳的電洞遷移率為3.96×10-3 cm2 V−1 s−1。

2,7-Diiodo-3,6-dibromofluorene and 2,7-dichloro-3,6-dibromofluorene have been successfully synthesized. The two key intermediates enable us to implement a regioselective Sonogashira reaction followed by intramolecular thiolate/acetylene cyclization, forming two regiospecific pentacyclic dithieno[2,3-b:7,6-b′]fluorene (2,7-DTF) and dithieno[3,2-b:6,7-b′]fluorene (3,6-DTF) isomeric molecules, respectively. By using a similar strategy, selenophene-based diselenopheno[2,3-b:7,6-b′]fluorene (2,7-DSF) as well as diselenopheno[3,2-b:6,7-b′]fluorene (3,6-DSF) were also prepared. The isomeric and sulfur/selenium effects determine the optical, electrochemical, and orbital properties. X-ray crystallography revealed that 2,7-DTF, 3,6-DTF, and 3,6-DSF molecules assemble into supramolecular helical structures. Moreover, the pentacyclic DTF monomers were polymerized with dithienodiketopyrrolopyrrole (DPP) acceptors to afford three alternating donor-acceptor copolymers PDTFDPP16, PDTFDPP20, and PDTFDPP32 incorporati-ng different aliphatic side chains (R1 group at DTF; R2 group at DPP moieties). The side-chain variations in the polymers play a significant role in determining not only the intrinsic molecular properties but also the intermolecular packing. According to the computational calculations, PDTFDPP16 with octyl (R1) and 2-ethylhexyl (R2) side chains exhibits linear polymer backbone but poor solubility which result in the lowest molecular weight of 4.5 kg/mol, whereas PDTFDPP32 with bulkier 2-butylhexyl (R1) and 2-octyldodecyl (R2) side chains shows the curved backbone and moderate molecular weight of 32 kg/mol. PDTFDPP20 with 2-butylhexyl (R1) and 2-ethylhexyl (R2) to improve the solubility without sterically suppressing polymerization resulted in quasi-linear backbone and thus the highest molecular weight of 68 kg/mol. As evidenced by the 2-dimensional GIXS measurements, PDTFDPP16 tends to align an edge-on π-stacking, whereas PDTFDPP20 adopts a predominately face-on orientation. PDTFDPP32 with the bulkiest side chans shows the less ordered amorphous character. The OFET device with bottom-gate/top-contact architecture using PDTFDPP20 achieved an unprecedentedly high hole-mobility up to 5 cm2V−1s−1 with a superior on/off ratio over 106. On the other hand, we present a facile synthesis to make a new ladder-type heptacyclic dithienobenzofluorene (DTBF) framework, where the central 2,7-fluorene unit is covalently fastened with two external thiophenes via two C=C bridges. A dieneyne-containing precursor undergoes DBU-induced double benzannulation to regiospecifically introduce two solubilizing 2-octyldodecyl side chains at 5,10-positions of DTBF. The rigid and coplanar Br-DTBF monomer with sufficient solubility was copolymerized with 5,6-difluoro-4,7-bis(5-(trimethylstannyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (Sn-DTFBT) and 5,10-bis(5-(trimethylstannyl)thiophen-2-yl)naphtho[1,2-c:5,6-c']bis([1,2,5]thiadiazole) (Sn-DTNT) via Stille coupling to furnish two donor-acceptor copolymers, PDTBFFBT and PDTBFNT, respectively. Their thermal, optical, electrochemical, molecular stacking and photovoltaic properties are investigated. PDTBFNT has higher molecular weight, smaller optical and electrochemical band gaps, and stronger solid-state packing than PDTBFFBT. Bulk heterojunction solar devices with the ITO/ZnO/polymers:PC71BM/MoO3/Ag configuration were fabricated. By adding 5 vol% diphenyl ether (DPE) as an additive, PDTBFNT:PC71BM and PDTBFFBT:PC71BM devices achieved the power conversion efficiency of 5.22% and 2.68%, respectively. The superior efficiency of PDTBFNT over PDTBFFBT is attributed to the better LUMO energy alignment between PDTBFNT and PC71BM and the face-on -stacking of PDTBFNT in the active layer. Moreover, PDTBFNT exhibited a higher field-effect transistor hole mobility of 1.90×10-2 cm2 V−1 s−1 than PDTBFFBT with 3.96×10-3 cm2 V−1 s−1.