Molecular Packing in Crystalline Polyfluorenes

黃聖恩(Sheng-En Huang)

指導教授 ： 蘇安仲

國立清華大學/工學院/化學工程學系/碩士(2009年)

摘要

本論文主要是研究poly(9,9-di-n-oxtyl-2,7-fluorene) (PFO)和poly(9,9-di-n-hexyl-2,7- fluorene) (PFH)的主鏈構形、分子堆疊和其光激發、放光之間的關聯。就主鏈構形而言，量子力學計算(Gaussian 03)之結果顯示: (1) PF系列主鏈之能隙隨單體之180度翻轉會略有差異，亦即簡單之C2對稱並不完全適用；(2) 相鄰單體偏離共平面約狰140o時為α相的最低能量單鏈構形。依此單鏈構形為基礎，我們的分子力學計算(Accelrys Cerius2)獲得與PFO及PFH之電子擇區繞射實驗圖案極為符合之計算結果，顯示PFO之α晶相為bi-radial II形式的側鏈構形而PFH之α晶相則為bi-radial I形式的側鏈構形，後者環抱相鄰主鏈的傾向較高。

關鍵字

分子堆積 ； PFO ； PFH ； α形式

並列摘要

Here we report results of our study of chain conformation, molecular packing, and corresponding effects on photo-excitation and luminescence behavior of poly(9,9-di-n-oxtyl-2,7- fluorene) (PFO) and poly(9,9-di-n-hexyl-2,7-fluorene) (PFH) using quantum mechanical (QM, Gaussian 03) and molecular mechanics (MM, Accelrys Cerius2) calculations. We demonstrate that the single-chain excitation energy can be slightly different upon pi-flipping of a fluorene monomer; this signifies difference between the two most likely (i.e., UDUD vs. DDUU) candidates for backbone conformation in the crystalline state. Excluding the DDUU conformation based on monomer length from MM, its tendency to bend from QM calculation, and symmetry requirement from crystallographic argument, we adopt UDUD conformation with alternating fluorene torsion angles of +_140 as the single chain conformation and proceed with MM simulation of chain packing in the α phase of PFO and PFH. Results agree well with experimental zone patterns from selected-area electron diffraction and indicate that the n-hexyl side-chains of PFH tend to take bi-radial I conformation whereas the octyl side-chains of PFO tend to take bi-radial II conformation. Due to differences in the preferred conformation, side-chains in PFH show stronger tendency to embrace a neighboring backbone than those in PFO.

並列關鍵字

molecular packing ； PFO ； PFH ； αform

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