由具矽烷基寡聚物之光物理性質研究相對應高分子之摺疊

設計並合成以甲基及異丙基之矽烷基為間隔且具有電子給體及受體的寡聚物，藉由研究其光物理性質探討相對應高分子之摺疊性。首先設計不對稱之電子給體(反-1,2-二苯乙烯)及受體(4-胺基苯乙烯)小分子，並逐步利用具空間選擇性之銠金屬催化矽氫化反應及中間體之矽氫基團的建立，進而反應得到對應之寡聚物(單體、二聚物、三聚物及四聚物)。　　實驗結果顯示，在甲基矽烷基為間隔之寡聚物的螢光光譜中具有來自電子給體與受體間電荷分離激發態的放光以及受體自身的螢光，其表現與甲基矽烷基高分子相似。進一步分析兩種放光的相對強度，隨著寡聚物的分子結構延長，來自於電荷分離激發態之放光強度顯著增加；再與兩種不同聚合度之高分子比較，隨著分子量的增加，放光強度與聚合度作圖逐漸顯示出一收斂的趨勢。　　此外，改變矽烷基上取代基團成較大的異丙基，單體及二聚物之光物理性質與甲基矽烷基之寡聚物和高分子並無顯著差異。然而，三聚物及四聚物的吸收光譜中出現了不同於電子給體及受體自身吸收之特徵峰。此特徵峰應來自於電荷轉移錯體的吸收。四聚物於螢光光譜中更顯示了與異丙基矽烷基高分子之電荷轉移錯體相似的放光。此電荷轉移錯體的形成可歸因於矽上較大的異丙基團取代及分子量的增加，促使矽原子周圍的構型產生變化，進而改變給體與受體間的電子作用力。　　上述實驗說明此類分子之摺疊性會影響矽烷基兩側電子給體及受體的電子耦合，進而影響光物理性質之表現。而分子之摺疊性可藉由矽上取代基團的改變及分子鏈長的延伸加以控制。

關鍵字

寡聚物；光致電子轉移；高分子摺疊；矽烷基間隔高分子； Thorpe-Ingold 效應

並列摘要

A series of oligomers with donor and acceptor moieties divided by different dialkylsilylene spacers (Me2Si- vs iPr2Si-) have been designed and synthesized to inspect the folding behavior of the corresponding copolymers by investigating their photophysical properties. 4-Aminostyrene moiety was chosen as the donor and stilbene moiety was selected as the acceptor. Sequential Rh-catalyzed hydrosilylation of terminal alkyne with silylhydride afforded these oligomers. Terminal alkynes were prepared by Sonogashira reaction. Silylhydrides were introduced by lithiation of corresponding aryl bromides with nBuLi followed by silylation with dialkylchlorosilanes. Unsymmetrical stilbenes and bisalkyne were delicately designed and synthesized for constructing these oligomers. Both local excited (LE) emission of the acceptor chromophore and emission from the charge-separated state (CT emission) have been observed in Me2Si-spaced oligomers, just like that of Me2Si-spaced copolymer. As degree of oligomerization increased, the relative intensity of the CT emission compared to LE emission of Me2Si-spaced oligomers displayed prominent enhancement. When compared with Me2Si-spaced copolymers with different degrees of polymerization (DP = 14 and DP = 30), this tendency reached a plateau rather than increased proportionally. On the other hand, albeit the bulky isopropyl group introduced on the silicon atom, iPr2Si-spaced monomer and dimer showed similar photophysical behaviors to those of Me2Si-spaced oligomers and copolymers. However, iPr2Si-spaced trimer and tetramer exhibited charge-transfer absorption, which is different from the intrinsic absorption of the donor and acceptor chromophores. Furthermore, tetramer showed essentially same emission from charge-transfer complex as that of iPr2Si-spaced copolymers. The charge-transfer complex emission is attributed to the strong electronic interaction between the donor and acceptor. The change of local conformation triggered by substitution of bulky isopropyl group on silicon atom and the extension of molecular structure resulted in this variation. These results suggest that the electronic interactions between adjacent donor and acceptor should be affected by the folding nature, which could be tuned by not only the steric effect of the substituents on the silicon atoms but also the extending molecular structures. In addition, the differences in the small energetic barriers for each of the conformational states may be amplified by extending the distance of the folding structure, thus resulting in a more stable conformation.

並列關鍵字

oligomer ； photoinduced electron transfer ； polymer folding ； silylene-spaced copolymer ； Thorpe-Ingold Effect

參考文獻

(50) 廖偉智，國立臺灣大學化學所碩士論文，2011.

(45) 葉美鈺，國立臺灣大學化學所博士論文，2007.

(15) West, R.; David, L. D.; Djurovich, P. I.; Stearley, K. L.; Srinivasan, K. S. V.; Yu, H. J. Am. Chem. Soc. 1981, 103, 7352-7354.

(31) Wang, H.-W.; Cheng, Y.-J.; Chen, C.-H.; Lim, T.-S.; Fann, W.; Lin, C.-L.; Chang, Y.-P.; Lin, K.-C.; Luh, T.-Y. Macromolecules 2007, 40, 2666-2671.

(1) Kekulé, A.; Ladenburg, A. Über die Konstitution und die Metamorphosen der Chemischen Verbindungen und über die Chemische Natur des Kohlenstoffs; Kessinger Publishing, 1904.

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由具矽烷基寡聚物之光物理性質研究相對應高分子之摺疊

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