- 學位論文
含噻吩多環芳香族分子之光環化合成與性質分析
Syntheses, Structures, and Property Studies of Polycyclic Heteroarenes via Oxidative Photocyclization
摘要
多環芳香族化合物擁有良好的共軛性及低能隙之特性，具有潛力成為新一代的半導體材料，可應用在有機場效電晶體，有機發光二極體，及有機太陽能電池等光電元件的開發上。近年來多環芳香族化合物被廣泛的研究，許多有機合成方法被用來開發新的分子結構，其中，利用光能使二苯乙烯衍生物 (stilbenoid) 環化產生菲 (phenanthrene) 的衍生物，是建構高共平面性共軛系統的經典方法之一。 在本論文中，我們利用簡單的合成步驟並以照光合環的方式成功得到一系列C2及C3對稱的含噻吩多環芳香族化合物，藉由將多種芳香環引入多環芳香族的共軛中心，來微調化合物的HOMO 及LUMO能階，並透過光物理與電化學性質的分析，進一步來探討分子結構與性質間的關係。我們發現不同對稱性的化合物在環化前後其性質有不同的改變：C2對稱的化合物相較於環化前的起始物而言，關環後的產物的吸收及放光光譜皆有藍移的現象，其HOMO能階在關環後也明顯下降；另一方面，C3對稱的化合物在關環前後其HOMO能階並無明顯的改變，反倒是其LUMO能階在關環後下降導致其吸收及放光波長皆產生紅移。此外，我們也發現因為照光導致的電環化反應使C3對稱的化合物具有光致變色的特性。
並列摘要
Polycyclic π-conjugated organic compounds have thrived over the past few decades because of their strong potential as superior semiconductors and versatile application in electronic devices, such as organic field-effect transistors (OTETs), organic light-emitting diodes (OLEDs), and photovoltaic cell. One of the classic synthetic methodologies for large aromatic systems is the oxidative photocyclization. In this regard, numerous successful cases based on using diarylethene or 2-vinylbiphenyl derivatives as the precursors have been reported. In this thesis, we accomplished an alternative synthetic route of novel thiophene-fused polycyclic structures utilizing vinyl groups substituted thiophene derivatives as the starting materials. Accordingly, we have prepared a new series of C2- and C3-symmetric polycyclic heteroacenes by UV-light irradiation in the presence of iodine. Delicate molecular designs conducted on the starting materials make specific sites available for subsequent ring closures. Structural identifications of heteroacenes and their precursors are based on X-ray crystal diffraction analysis. The photophysical and electrochemical properties are characterized by studying their UV-Vis/photoluminescence (PL) and cyclic voltammetry (CV), respectively. Various aromatic rings including thiophene, 2,1,3-benzothiadiazole, and quinoxaline were incorporated as the central linkage, giving the opportunities for tailoring the HOMO/LUMO energy levels of the cyclized products. Interestingly, we found that different symmetry of molecules gives rise to distinct characters. There is a bathochromic effect in absorption as well as emission spectra of C3-symmetric compounds featuring with lower LUMO energy levels after ring closure. On the other hand, in the case of C2-symmetric system, the absorption and emission bands blue-shift, where the HOMO energy levels of cyclized compounds become much lower, whereas the LUMO energy level remains intact or slightly shifts to higher levels. In addition, we reported the solvent effects of photocyclization reaction and the photochromism-like property of C3 symmetric compound in this thesis.
參考文獻
延伸閱讀
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