Thorpe-Ingold效應對於亞矽基雙乙烯基芳香環聚合物的構型影響

Abstract

利用銠金屬催化的矽氫化反應可以合成一系列有規則以矽烷基為間隔將不同發光團隔開並且交錯排列的芳香基聚合物 [(donor)-SiR2-(acceptor)-SiR2-]。以鎳金屬催化硫縮醛芳香化合物與格林那試劑偶合反應可以方便的得到乙烯基矽基醚，再經由氫化鋁鋰還原反應，可得到相對應甲基取代的矽基氫化合物。另外，將雙乙烯基溴與第三丁基鋰作用後再與氯化二異丙基矽烷進行親核取代反應，則得到相對應異丙基取代的矽基氫化合物。不同於大部分的共聚合物，我們的合成策略提供了一個很有效的方法來建構有精確位置化學及重複規則排列的聚合物。具有與聚合物相同發光團的參考單體也被製備用以作為光物理性質的比較，矽原子在聚合物中扮演一絕緣體角色來連接不同的發光團。 我們完成了利用Thorpe-Ingold效應的概念來調整以矽烷基為間隔物之聚合物的構型和柔軟度，由STM影像可以得到甲基取代的聚合物較鬆散而異丙基取代的聚合物較為捲曲，在光物理研究上亦可以得到一致的結果，由於異丙基為較大的取代基故能使得發色團與發色團間的距離變近，因此可以觀察到異丙基取代的聚合物有較明顯的分子內聚集之現象(藍光範圍放射強度明顯變大)。延續此結果，我們將此類聚合物用在對距離敏感的能量轉移和電子轉移上，實驗結果顯示在能量轉移的研究上並無很大的差別，而在電子轉移的研究裡，由於異丙基取代的聚合物可以使發色團間的距離變近，因此可以得到更高效率的電子轉移，此結果同樣也可以在STM影像中被觀察到。 最後我們合成出包含三種不同發色團的聚合物，我們可以觀察到連續的能量與電子轉移現象發生在這個以矽烷基為間隔且交替排列的聚合物系統中。

A series of regioregular silylene-spaced alternating donor-acceptor arene copolymers [(donor)-SiR2-(acceptor)-SiR2-]n was synthesized by rhodium catalyzed hydrosilylation of bis-alkynes with bis-silylhydride. Methyl-substituted vinylsilylhydrides were prepared by nickel-catalyzed olefination of the corresponding aryl dithioacetals with Grignard reagent followed by LAH reduction. In addition, isopropyl-substituted vinylsilylhydrides were obtained from the displacement of (iPr)2HSiCl with aryl-vinyllithium. Unlike most copolymers, our strategy has furnished a powerful arsenal for the construction of copolymers with precise regiochemistry and repetitive units. The silylene group serves as an insulating building block between chromophores. We carried out the first example using the concept of Thorpe-Ingold effect to direct the conformation and may be the softness of silylene-spaced divinylarene copolymers. The results from the STM images are consistent with the outcome of photophysical studies of these polymers. Copolymers with bulky isopropyl substituents are more folded to bring the chromophores in closer proximity, and therefore intrachain interactions between these chromophores will become more prominent leading to enhancement in aggregation emission. Since distance is known to play an important role in photo-induced electron transfer (PET) processes, the present investigation suggested that bulkier substituents on silicon would bring the chromophores in closer proximity. Copolymers with bulky isopropyl substituent are more folded so that intrachain PET between these chromophores become more dominant to result in more efficient fluorescence quenching. The results from the STM images are also consistent with the photophysical data of these polymers. In addition, the polymer composed of three different chromophores have been synthesized, the sequential energy and electron transfer along the polymeric chain was also observed.