以二噻吩并苯并噻二唑為主幹之共軛小分子與高分子之合成與性質探討

Abstract

本文主要設計、合成及分析一系列以含二噻吩并苯并噻二唑為主體之有機共軛高分子與小分子，探討分子結構對於材料性質的影響，以開發新型高性能共軛高分子與小分子材料為目標。 我們的研究主要分為兩個部分，首先在第一個部分，我們合成以二噻吩并苯并噻二唑為主體之高分子P(DTBTD-3EHT-BT-hex)，藉由增加烷基鏈的方式解決溶解度與無法進行性質測量的問題；P(DTBTD-3EHT-BT-hex)的光學吸收範圍落在300-550 nm處，X光繞射分析實驗證實P(DTBTD-3EHT-BT-hex)形成薄膜時無結晶性；此高分子延續二噻吩并苯并噻二唑之特性具有低HOMO能階，然而其LUMO能階則相對較高；我們提出一些結構再修飾的方法期盼未來該結構應用於有機太陽能電池可以有光電轉換效率的突破。 第二部分，延續第一部分的實驗結構，我們合成一系列含有二噻吩并苯并噻二唑之共軛小分子DTBTD-terT-hex、DTBTD-hex-BF與DTBTD-2,3-DDec-terT，三者材料溶液狀態下主要的吸收光譜範圍皆落在400~550 nm間，成膜後DTBTD-terT-hex結構光學最大吸收峰紅位移達約600 nm處，且光學與電化學能隙為三種材料中數值最小；而在能階的部份隨著增加兩側之結構，HOMO能階依然維持於約-5.3 eV至-5.4 eV之間；分子堆疊的部份DTBTD-terT-hex與DTBTD-hex-BF承襲二噻吩并苯并噻二唑良好的共平面性，在X光繞射圖譜分析得知兩種材料皆具結晶性，表示分子在堆疊上有規則的排列。 綜合以上實驗，我們對於含二噻吩并苯并噻二唑之共軛高分子與小分子的結構設計將有更進一步的認識與了解，這將有助於未來設計高性能之含苯并噻二唑衍生物材料。

In this thesis, a series of novel conjugated polymers and small molecules with dithienobenzothiadiazole (DTBTD), as structural core unit were designed and synthesized by Stille coupling and Suzuki coupling reactions. The correlations between the molecular structure packing, optical and electrochemical properties were investigated. This thesis has been divided into two parts. In the first part, conjugated polymers containing dithienobenzothiadiazole (DTBTD) as an acceptor moieties and bithiophene (BT) and dihexyl-bithiophene (BT-hex) as donor moieties were designed and synthesized using stille cross-coupling reaction. The solubility, optical absorption spectra, X-ray diffraction spectra (XRD) and electrochemical properties of the resulting polymer P(DTBTD-3EHT-BT-hex) were characterized. The solubility of the P(DTBTD-3EHT-BT-hex) polymer is significantly improved as compared to the nonalkylated P(DTBTD-3EHT-BT) polymer. In solution, P(DTBTD-3EHT-BT-hex) exhibited broad absorption covering the range from 300 to 600 nm and with the optical band gap of 1.98 eV. The energy levels of P(DTBTD-3EHT-BT-hex) polymer possesses low-lying HOMO energy level which is about -5.46 eV. Results of XRD data revealed amorphous nature of the P(DTBTD-3EHT-BT-hex) polymer. We proposed that the side chain structural modification approach can advance better designing for conjugated polymers with high power conversion efficiency. Based on the first part of our results, we further designed and synthesized a new series of conjugated small molecules such as DTBTD-terT-hex, DTBTD-hex-BF and DTBTD-2,3-DDec-terT with dithienobenzothiadiazole as a acceptor unit, and terthiophene and benzofuran as the donor side group. The impact of these different donor side groups on their solubility, optical, XRD and electrochemical properties were investigated. The physical properties of the synthesized small molecules showed good solubility, broad absorption bands within the range from 300 to 650 nm, and optical band gaps of 1.89 eV, 2.10 eV and 1.98 eV for DTBTD-terT-hex, DTBTD-hex-BF and DTBTD-2,3-DDec-terT, respectively. Furthermore, DTBTD-terT-hex displayed red shift absorption band compared to other small molecules. The XRD results clearly indicate that the structure of DTBTD-terT-hex and DTBTD-hex-BF have regular packing and good crystallinity when compared to the DTBTD-2,3-DDec-terT. These findings offer valuable guideline for further designing dithienobenzothiadiazole based small molecules to develop high-performance BHJ organic photovoltaic cells. In summary, we have successfully designed, synthesized and characterized a family of polymers and small molecules containing dithienobenzothiadiazole as a acceptor unit. The achievement of structure-property correlations will be benefit of developing high performance conjugated semiconductor materials.