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標題: | 矽烷基間隔之胺基苯乙烯-二苯乙烯計合物之理論探究:由單體至寡聚體之構形與光物理性質變化 Theoretical Study on Alternating Dialkylsilylene- Spaced Aminostyrene-Stilbene Co-oligomers: Evolution of Conformations and Photophysics from Monomers to Oligomers |
作者: | Yen-Chin Huang 黃彥欽 |
指導教授: | 鄭原忠(Yuan-Chung Cheng) |
關鍵字: | 含矽聚合物,密度泛函理論,光物理,勢能面,碳-氮鍵旋轉,構形分析,聚合物折疊行為, silylene-based polymer,density functional theory,photophysics,potential energy surface,C-N bond rotation,conformational analysis,polymer folding, |
出版年 : | 2019 |
學位: | 博士 |
摘要: | 在本篇論文中,我們利用理論計算方法,試圖釐清以矽烷基間隔之胺基苯乙烯-二苯乙烯共聚物(DAD-n)系統在光譜實驗中所觀測到的光物理現象其背後的機制,並理解取代基的立體障礙變化是透過怎樣的作用機制來影響聚合物的折疊行為與所對應的光物理性質。我們由發色團單體STIL與DMAS出發,逐漸加大系統至二聚體DA與DD,以及寡聚體ADDA,來分析這些分子系統其構形變化與基團堆疊形式,與光物理性質之間的關聯。
在發色團單體的層次,我們藉由B3LYP-D3/6-31+G(d)層級的DFT/TDDFT計算,針對發色團單體STIL與DMAS兩系統進行其結構與光物理性質的理論研究,並取得發色團單體的剛性結構特徵與光物理性質數據作為後續研究的基礎。我們也透過構形分析,將二聚體DA與DD系統所有可能的穩定構形加以分類,計算其結構參數以進行分析比較。並透過TDDFT/B3LYP-D3/6-31+G(d)層級的計算,來獲得二聚體DA-Me與DA-Pr所有可能構形的基態穩定結構與激發態穩定結構(ES1結構、ES2結構、ES3結構、與TICT結構)與相對應的光物理性質,並提出一個共通且並不受初始構形影響的光譜動力學模型,來解釋在二聚體DA-Me與DA-Pr在實驗中的吸收光譜與放射光譜所發現的吸收或放射現象。此外,我們證實了透過碳-氮鍵的旋轉,有助於各激發態之間進行內轉換。而根據計算結果,我們認為亞矽基上的立體障礙與DMA基團的位向限制,也許是聚合物DAD-p-Pr與DAD-p-Me擁有不同性質的CT放射峰的原因之一。 針對寡聚體ADDA系統,我們利用粗粒度模型的概念,結合PM7量子半經驗方法的計算與平均連結聚合演算法的群集分析,來進行系統性構形分析。依據折疊程度的不同,ADDA-Me與ADDA-Pr系統的整體構形皆可由折疊構形到非折疊構形分成5類群集,並發現ADDA-Me系統以具褶板結構的M1群集較為穩定,但ADDA-Pr系統以具螺旋結構的P2群集的平均相對能量較低。我們推測寡聚體ADDA-Me的吸光性質主要應該來自於褶板結構,而寡聚體ADDA-Pr的吸光性質主要應該來自於螺旋結構的貢獻。 對DA系統來說,Thorpe-Ingold效應改變了順式與反式構形的比例。DA-Pr系統較DA-Me系統擁有更高比例的順式構形,但同時也具有較高的構形轉換間能量障礙。而對ADDA系統來說,Thorpe-Ingold效應則是調控折疊構形中褶板結構與螺旋結構的比例。ADDA-Pr系統較ADDA-Me系統擁有更高比例的螺旋結構。此外,發色團基團本身的剛性也是寡聚體折疊結構穩定的因素之一。因此Thorpe-Ingold效應對於DAD-p系統的影響,可歸因成兩個層面:(i)因烷基立體障礙的改變,影響DA接點本身的對稱性與佔據的空間,進而改變兩側發色團可穩定的相對位向,造成順式/反式構形比例的增減。(ii)因烷基立體障礙的改變,產生透過空間的交互作用,來影響折疊結構的穩定度。 In this thesis, we applied theoretical calculations to investigate the origins of photophysical properties in spectral experiments of alternating dialkylsilylene-spaced aminostyrene-stilbene co-oligomers (DAD-n), and realized the role of the steric effect of substituent in the polymer folding. We analyzed and explained the relationship between the conformations and photophysical properties of the chromophore monomers STIL and DMAS, dimers DA and DD, and oligomers ADDA. We collected the structural and photophysical information of chromophore monomers STIL and DMAS with DFT/TDDFT calculations at the B3LYP-D3/6-31+G(d) level. Our results explained the rigid structure characteristics and photophysical properties of STIL and DMAS monomers, which were regarded as the foundation of further researches. We also used conformational analysis to explore all possible stable conformers, cluster them, calculate the structural parameters of them, and finally analyze and compare them. We used DFT/TDDFT calculations at the B3LYP-D3/6-31+G(d) level to optimize the stable structures on the ground state and first three excited states (GS structure, ES1 structure, ES2 structure, ES3 structure, and TICT structure), then studied the corresponding photophysical properties. We showed a general photophysical behavior, which were not affected by the initial conformations, to explain the absorptions and emissions in the experimental spectra. We also confirmed that C-N bond rotation played an important role for internal conversion between excited states. Based on our calculation results, we thought the steric effect of dialkylsilylene group and the orientation of DMA group might lead to CT bands with different photophysical properties in DAD-p-Me and DAD-p-Pr systems To explore conformational states of oligomers, we combined the concept of coarse-grained modeling, PM7 semi-empirical method, and cluster analysis with average-linkage agglomerative algorithm, to perform the systematic conformational analysis. According to the degrees of oligomer folding, all conformers of ADDA-Me (or ADDA-Pr) could be divided into five clusters including folding conformations and extended conformations. We found the sheet-like cluster was the most stable cluster in the ADDA-Me system, but the helix-like cluster had the lowest average relative energy in the ADDA-Pr system. For the dimer DA system, We revealed that the role of Thorpe-Ingold effect is to change the ratio of anti/syn conformations. Compared with DA-Me system, DA-Pr system had higher percentages of syn conformers, but also had higher energy barrier of interconversion between the anti form and the syn form. For the oligomer ADDA system, Thorpe-Ingold effect controlled the ratio of sheet-like and helix-like conformers. ADDA-Pr system exhibited higher ratio of helix-like conformers compared with ADDA-Me system. Based on the concept of coarse-grained modeling, the rigidity of chromophore was also a factor of stabilization of oligomer folding. According to preliminary results of our calculations, the conformations and photophysics of DAD-p system controlled by Thorpe-Ingold effect could be summarized into two aspects:(i) The steric change of alkyl substituents affected the symmetry and filled space of DA joint, then the orientation of two chromophores would be changed, and finally the increase or decrease of anti/syn conformer ratio occurred. (ii) Through-space interaction from the steric change of alkyl substituents affected the stability of folding structure directly. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/74021 |
DOI: | 10.6342/NTU201903073 |
全文授權: | 有償授權 |
顯示於系所單位: | 化學系 |
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