利用分子動力學模擬及量子力學計算探討聚噻吩高分子中改變側鏈噻吩環數對於分子鏈構形、堆疊排列以及電荷傳遞性質的影響

Abstract

我們利用分子動力學模擬以及量子力學計算，探討聚3-己烷噻吩( Poly(3-Hexylthiophene)，P3HT)系統中側鏈上共軛噻吩環數目的增加，如何影響有序堆疊狀態下其分子鏈構形、堆疊排列情形以及載子遷移率，並且和P3HT系統做比較。本實驗所模擬的聚噻吩材料(A1~A4)都有著四種排列類型(Type I~ Type IV)，我們都在Type II類型上發現到最低的能量以及規整的排列堆疊現象，隨著軛噻吩環數目的增加，主鏈與側鏈都各自有很規整的堆疊排列與共平面狀態。而我們發現主鏈噻吩環與側鏈噻吩環之間有著偏離共平面的扭轉情形，是由於主鏈側鏈噻吩間的凡得瓦斥力造成的立體效應所導致。在量子力學計算部分，我們會以分子鏈上及分子鏈間這兩個不同的電荷傳遞方向來進行分析，探討載子遷移率如何受到主側鏈扭轉角度分佈以及分子鏈間距離與錯位距離的影響。我們觀察到A1材料在分子鏈上的載子遷移率是低於P3HT的速率，但在分子鏈間系統則是有較高的現象，並且發現在A1材料中，載子沿著π-π堆疊方向的載子遷移率明顯低於沿主鏈方向的速率，因此，A1材料整體的載子遷移率是低於P3HT的速率，且載子的主要傳輸路徑是沿著主鏈的方向而非沿鏈間的方向，這與P3HT的載子遷移率有著相同的結果。

We use molecular dynamics and quantum mechanical calculations to explore the system of Poly (3-Hexylthiophene) P3HT which contains different numbers of side chain thiophenes. We compare our system and P3HT system with respect to the conformations of polymer chains, stacking, and charge mobility. In this study, there are four types, type I~ Type IV , in different materials, A1~A4. We found all the Type II have the lowest energy and regular stacking. As the numbers of thiophenes increase, both main chain and side chain have regular arrangement and maintain obviously coplanar conformation. We found main chain and the side chain deviates from their initial coplanar plane. This is due to steric repulsion arose from Van der Waals interaction. In quantum mechanical calculations, we discuss the charge mobility in different directions along intrachains and interchain. Main chain and side chain torsion angle distribution, interchain distance, and shift distance are all variables to effect the charge mobility. We observe that the hole mobility of A1 is less in intrachain but higher in interchain than the hole mobility of P3HT. We also found that hole mobility along intrachain extremely higher than in interchain. The result that the charge transfer route is along the intrachain instead of interchain is the same as P3HT elucidate that the hole mobility of A1 is less than P3HT.