Abstract
本研究以分子模擬技術，探討聚(3-烷基□吩)分子排列的模式，及其受溫 度之影響。本文中使用半經驗量子化學計算法MNDO及PM3作為量子化學計 算方法，以MSI (Molecular Simulation Inc.)所出版的POLYGRAF套裝軟 體計算Molecular Mechanics及Molecular Dynamics，而使用其CERIUS套 裝軟體則以計算X-ray繞射圖譜。經由對順向及非順向的聚(3-烷基□吩) 的分子模擬及XRD圖譜的計算，發現在烷基側鏈及主鏈的堆疊中的確存有 不規則度。藉由分子動力學模擬的輔助，可以模擬並觀察單位晶格內的不 規則度。以Inverse Comb為藍本在側鏈及主鏈加入不規則度的晶體結構非 常符合實驗的結果。熱攪動是產生此種不規則度的主因，在室溫時烷基側 鏈的熱運動影響了共軛主鏈的構形。並隨著烷基側鏈長度的增長，其對共 軛主鏈的構形影響亦增大。本研究亦計算隨溫度改變的分子構形變化情形 ，而模擬的溫度範圍自-130oC至125oC。當溫度增加時，烷基側鏈趨向躺 在由近似共平面主鏈所構成的平面上，然而單位晶格內的分子排列並無明 顯的改變。當溫度自-130oC上升到125oC時，聚(3-十二烷基□吩)烷基側 鏈gauche形式的分率從10%增加至約25%。在溫度55oC到85oC之間，主鏈扭 曲角的z平均值有一自30o到35o的角度轉換，此項過渡轉變與自UV-vis光 譜所觀察到的熱變色現象之過渡轉變溫度範圍相互吻合。聚□吩的變溫模 擬結果則顯示無烷基側鏈存在時，溫度的升高並不會使□吩主鏈的分子構 形產生過渡轉變。根據量子化學計算的結果，可以推知random coil構形 的聚(3-烷基□吩)並不存在，聚(3-烷基□吩)分子排列有規則及次規則二 相。對於二相之分子構形後者無規則排列，且其中□吩主鏈存在有少許的 高扭曲角。當聚(3-十二烷基□吩)晶體結構被加溫時，首先產生m2構形至 m1構形類型的轉變，再產生m1構形的平均扭轉角的變化。 The molecular simulation is performed for studying the molecular arrangement of poly(3-alkylthiophene)s (P3ATs) in unit cell at various temperature. By incorporation of molecular dynamics calculation to the XRD calculation of oriented and non- oriented P3ATs based on "Inverse Comb" model. it is found that the disordering do exist both in alkyl side chains and main chains in the unit cell. The calculated XRD with the consideration of disorder both in side chains and main chains is in agreement with the experimental results. Such the structure disordering is resulted from thermal motion of alkyl side chains, and appears even at room temperature. A transition of z-averaged torsion angle of the main chains from 30o to 35o occurs in the temperature range from 55oC to 85oC, which is consistent with the increase in the energy of absorption maximum during the transition range, 50oC to 100oC, as determined from its UV-vis spectra. The bulk P3ATs have two phases, ordering and less-ordering phases. As to the molecular conformation the latter is less ordering. There is few subchains with high torsion angles existing in less-ordering phase. As the temperature is higher than Tm, the layer structure of the ordering phase is destroyed because of the high torsion angles of main chains, and changes into less- ordering phase. As P3ATs is heated from low temperature, the conformation of P3ATs first changes from m2 type to m1 type, then the averaged torsion angle of m1 type chains increases.