合成以及探討側鏈含氟原子的P3TTPD系列予體－受體共軛交替共聚物之性質

Abstract

具有光電性質的予體－受體共軛交替共聚物，可應用於輕便、可饒式有機光電元件。因此如何使共聚物有效的自組裝形成長程有序的結構，並促進光電元件的效能是重要的研究領域。在先前的研究中，柔軟的寡醚基側鏈被證實具有能力幫助共聚物形成長程有序的結構。然而，寡醚基的親水性卻不利應用於敏感的電子元件。 在本研究中，透過側鏈工程，我們設計並合成新的共軛共聚物，其不僅可以有效調控共聚物的疏水性與穩定性，更可以改變共聚物的自組裝構型與光電性質。以terthiophene（3T）為予體及thieno[3,4-c]pyrrole-4,6-dione（TPD）為受體，並在3T引入三種側鏈：烷基（R1）、半氟烷（SF）或全氟烷（F）；TPD引入烷基側鏈（R2）或寡醚基側鏈（E），經由Stille coupling反應合成六種予體−受體共軛交替共聚物。而共聚物之性質分別以接觸角、掠角X光廣角散射、紫外−可見光光譜、循環伏安法及熱重分析進行探討。 不論TPD上側鏈為R2或E，由實驗發現共聚物隨3T上SF與F的氟原子多寡，逐步提升共聚物的疏水性。自組裝部分，所有共聚物經熱退火後皆形成熱力學上較穩定之結晶，其中3T上為R1之共聚物呈現六角柱結構；為SF與F之共聚物則呈現層板結構。光電性質部分，共聚物隨3T上SF與F的氟原子多寡，逐步擴大能隙，使薄膜最大吸收光波長（λmaxfilm）藍移，並連帶降低了最高佔據分子軌域（EHOMO）與最低未佔據分子軌域（ELUMO）。熱穩定性方面，共聚物同樣隨3T上SF與F的氟原子多寡，逐步提升熱穩定性。另一方面，不論3T之側鏈，比較TPD為R2與E之共聚物發現E之親水性僅使接觸角小幅下降。自組裝方面，E之柔軟性幫助共聚物形成更加規整的形貌。光電性質則有較小的能隙以及較高的EHOMO及ELUMO。熱性質則較R2差。 綜觀整個實驗結果，我們透過SF與F側鏈有效提升共聚物的疏水性及熱穩定性，同時也大幅影響自組裝與光電性質。含氟側鏈之共聚物經熱退火皆自組裝成熱力學穩定的層板結構，應可有較佳的電性，具有應用於氣體感測元件及場效電晶體的潛力。

Optoelectronic active conjugated donor-acceptor alternating copolymers have potential in the applications of lightweight and flexible optoelectronic devices. How to design polymers that can be self-assembled into long-range highly ordered structures and to enhance the performance of devices is a very important research field. Previous research showed that the oligoether side chain can promote the long-range ordered structures in copolymers. However, the hydrophilicity of oligoether limits the copolymer to be fabricated into high sensitivity devices. In this research, through side chain engineering, we design and synthesize new copolymers containing fluoroalkyl side chain. They can exhibit not only long-range ordered structures and good optoelectronic property but also exceptional hydrophobic property and thermal stability. We choose terthiophene (3T) as donor and thieno[3,4-c]pyrrole-4,6-dione（TPD）as acceptor to build alternating copolymers. Three kinds of side chains: alkyl (R1), semifluoroalkyl (SF) and perfluoroalkyl (F) are placed on 3T respectively; alkyl side chain (R2) and oligoether side chain (E) are placed on TPD respectively. Through Stille coupling reaction, six polymers are synthesized. The properties of polymers were investigated by contact angle measurement, glancing incident wide angle scattering spectroscopy, UV-Vis spectroscopy, cyclic voltammetry and thermal analysis. Regardless the side chain type is R2 or E on TPD, the contact angle is increased with increasing the amount of F on the side chain of 3T. Upon annealing, the polymers contain R2 side chain self-assembled into hexagonal cylinder structure. The structure is changed to lamella for the copolymers containing either SF or F side chain. By increasing the amount of F on the side chain, the blue shift of λmax of UV-Vis absorption is increased; EHOMO and ELUMO levels are lowered; the thermal stability (Td) is increased. On the contrary, regardless the side chain type on 3T, decreased contact angle, thermal stability and bandgap are observed for polymers with E side chain as compared with R2 side chain. However, the E side chain improves the extent of structure ordering and increasing EHOMO and ELUMO levels of the copolymers. In conclusion, we effectively improve the hydrophobicity and thermal stability of oligoether side chain on TPD of 3T-TPD alternating copolymer by placing either semifluoro or perfluoro alkyl side chain on 3T. Their self-assembly behaviors and optoelectronic properties of copolymers are also altered. The formation of highly ordered long-range lamella structure for new fluoro-containing copolymers will promote the charge transport that will be useful in the applications of sensors and transistors.