| 摘要: | 本論文設計並成功合成出三個系列的模型分子，第一系列為含有苯並?二唑(benzothiadiazole)結構單元之對稱型分子；第二系列為含有?喔?(quinoxaline)結構單元的四叉對稱型分子；第三系列為含有苯並?唑(benzothiazole)結構單元之模型分子。透過線性光學的實驗測量，可以瞭解模型分子的吸收波長、螢光波長等基本性質；而透過非線性光學的實驗測量，來證實模型分子具有多光子吸收的性質，分析實驗數據以及分子結構間的關聯性，我們可以統整出以下結論：
1. 以D-π-A-π-D設計的第一系列對稱型模型分子，具有良好的螢光產率，隨著增加三鍵的共軛，螢光波長也有隨之紅移的趨勢；而三鍵做為π-bridge能有效的提升雙、三光子吸收效率。以4,4′-dimethoxyfluorenylamine作為推電子基對於分子的雙、三光子吸收效率是明顯優於4,4′-dimethoxytriphenylamine的。
2. 第二系列分子具有quinoxaline中心結構，此系列擁有不錯的螢光產率，在中心quinoxaline接上methoxy官能基，會降低quinoxaline拉電子能力，造成螢光波長藍移，並且會抑制雙光子吸收效率。在diphenylaminofluorenyl外銜接上methoxy的官能基，會增加推電子能力，造成螢光波長紅移，對於雙光子吸收效率有顯著的提升。若是增加三鍵做為π-bridge有助於提升雙光子吸收效率。然而methoxy及三鍵結構上的微調在三光子吸收效率上的正負影響則不一定與雙光子吸收效率同步。
3. 第三系列不對稱型分子含有benzothiazole結構，螢光產率有優異的表現，若加入thiophene單元去提升共軛長度，可使螢光波長紅移，且能夠增加雙、三光子吸收效率。若加入三鍵結構去增加共軛長度，反而會抑制雙、三光子吸收效率。和triazolopyridine比較，若以benzothiazole為拉電子基，其螢光波長有明顯的紅移，且在雙、三光子吸收效率上benzothiazole優於triazolopyridine。
整體來說，如果想要提升雙光子吸收效率，推電子基可使用4,4′-
dimethoxyfluorenylamine，而π-bridge則可以引入thiophene單元或是三鍵結構，至於拉電子基則可以選擇benzothiazole及不含methoxy官能基之quinoxaline結構來組合成最終染料分子；如果想要提升三光子吸收效率， 4,4′-dimethoxyfluorenylamine仍然是個良好的選擇，而π-bridge的部分則可以加入thiophene單元，拉電子基則可以使用benzothiazole結構。儘管分析出提升雙、三光子吸收效率各自適合的官能基，但對於同時提升雙、三光子效率的分子設計要求，可能還是有不同的部分需要研究。
;Three model compound systems are designed and successfully synthesized in this thesis. The first system contains the benzothiadiazole structural unit. The second system is composed of the quinoxaline structural unit, and the third system is constructed based on the benzothiazole structural unit. We have measured the linear and nonlinear optical properties of these compounds. Some features are found about the relationship between molecular structure and optical properties and can be listed as follows:
1. For the first series of model chromophores, the structure based on D-π-A-π-D has lead to good quantum yield. The insertion of C-C triple bond into the conjugation has resulted in a red-shift of fluorescence. Also, this insertion of triple bond was found to have positive impact to two- and three-photon efficiencies. On the other hand, diphenylaminofluorenyl is a better electron-donor for the promotion of multiphoton efficiencies compared to a triphenylamine group.
2. For the second series of model chromophores, the structure contains the units of quinoxaline which exhibt good quantum yield also. The addition of methoxy group into the central quinoxaline unit causes a blue-shift of fluorescence and a decrease of the two-photon efficiency. When the diphenylaminofluorenyl is attached by methoxy groups, it will lead to a red-shift of fluorescence and increase the two-photon efficiencies. While three-photon efficiencies does not work in the same way. On the other hand, when the C-C triple bond is inserted into the conjugation, it results in a red-shift of fluorescence. Also, the insertion of triple bond will improve the two-photon efficiencies but the three-photon efficiency does not show the same trend, neither.
3. From the third series of model chromophores, it is found that the addition of thiophene unit into the conjugated framework can promote both two- and three-photon efficiencies. Interestingly, the insertion of C-C triple bond decreases the two- and three-photon efficiencies of these model compunds. Compared to triazolopyridine unit, benzothiazole is a better eletron-acceptor which possesses large improvement on the two- and three-photon efficiencies.
Overall, if we desire to enhance the two-photon efficiencies, we can select 4,4′-dimethoxyfluorenylamine as the donating group, Thiophene or C-C triple bond as the π-bridge, and benzothiazole or quinoxaline as the acceptors. If we need to improve the three-photon efficiencies, we can utilize 4,4′-dimethoxyfluorenylamine as the donating group, thiophene as the π-bridge, and benzothiazole as the acceptors. Based on the current investigation, we suspect that the requirements for the molecular design toward enhanced two- and three-photon efficiencies should be intrinsically different. |
