探討含有電子受體接枝於側鏈或主鏈上之共軛高分子的分子構形與其光電性質的相關性

Exploring the correlation between molecular conformation and optoelectronic properties of conjugated polymers:side-chain versus main-chain electron acceptors

黃榆臻(Yu-Chen Huang)

指導教授 ： 黃慶怡

國立臺灣大學/工學院/高分子科學與工程學研究所/博士(2014年)

https://doi.org/10.6342/NTU.2014.02329

摘要

我們運用全原子分子動力學(AAMD)模擬方法來得到高分子鏈構形與堆疊排列行為於有序狀態狀態；進而利用量子力學(QM)模擬方法來研究包含有電子予體與電子受體之共軛高分子構形與紫外光-可見光之吸收光譜的關聯性。我們選擇主鏈均由硫環所組成之高分子 Poly (3-dodecylthiophene-2,5-diyl) (P3DT)系列及有包含電子予體與電子受體之 Poly{bi(dodecyl)thio-phene-thieno [3,4-c] pyrrole-4,6 -dione} ( PBTTPD)系列相互比較。
首先，我們藉由觀察全原子分子動力學所得到在有序狀態下之高分子構形，我們得知當只有主鏈上擁有共軛硫環時，由於π-π作用力的關係導致於P3DT-HT傾向維持共平面之構形在堆疊狀態下。且由於位向選擇性的關係，P3DT-HH的主鏈上硫環呈現較大的扭轉偏離共平面現象。然而，就PBTTPD系列而言，由於TPD基團呈現了些微的立體阻礙，導致於PBTTPD-M與PBTTPD-S系列呈現較無序狀態。觀察P3DT-HT與P3DT-HH在堆疊狀態下之紫外光-可見光吸收光譜，可發現皆呈現一個訊號峰並且其吸收範圍為350nm~800nm；且明顯觀察到P3DT-HT比P3DT-HH之吸收光譜呈現紅位移現象。而當P3DT在主鏈方向接枝上電子受體基團(TPD)，可觀察到PBTTPD-M系列也呈現相似的吸收峰趨勢並且呈現一個訊號峰並且其吸收範圍為300nm~750nm。相反的，當P3DT在側鏈方向接枝上電子受體基團(TPD)，可觀察到PBTTPD-S系列反而在300nm~450nm吸收範圍裡有出現較小之訊號峰。
由紫外光-可見光之吸收光譜之結果可觀察到當電子受體接枝在主鏈方向或是在側鏈方向對於其分子構形有明顯的關聯性。由結果表明出當P3DT在主鏈方向接枝上電子受體(TPD)時，其整體的吸收光譜範圍變得更為廣泛，主要為其整體的共軛長度會被延伸；而當P3DT在側鏈方向接枝上電子受體(TPD)時，其整體的吸收光譜範圍也會變得更廣泛，但特別是增加在短波長區之訊號峰。並且可觀察到在堆疊狀態下，PBTTPD-M (HT 與 HH)之吸收訊號峰皆呈現比PBTTPD-S (HT 與 HH)落在吸收光譜之長波長區域。且由P3DT-HT 與 PBTTPD-M -HT在堆疊狀態下之紫外光-可見光之模擬光譜結果與實驗結果相互比較，發現兩者之間呈現相當良好的趨勢。

關鍵字

PBTTPD ； 電子予體-電子受體對 ； 光電性質

並列摘要

We employed the quantum mechanical (QM) and all-atom molecular dynamics (AAMD) simulation methods to examine the correlation between the molecular conformation and the UV-visible absorption behaviors of the donor-accepter pairs -based conjugated polymers. We have examined two model systems here, Poly (3-dodecylthiophene-2,5-diyl) (P3DT) of Poly{bi(dodecyl)thio-phene-thieno [3,4-c] pyrrole-4,6-dione}( PBTTPD). We focus on the effects of molecular regioselectivity and the PBTTPD molecules with acceptor unit (TPD) on either main (PBTTPD-M) or side chain (PBTTPD-S).
First, we observe the molecular conformation displaying regular packing of polymer chains via AAMD. When the conjugated thiophenes exist only along the main chains, the ordered molecules of P3DT-HT tend to keep a coplanar trans conformation due to the π-π attractions. Because of the molecular regioselectivity, the P3DT-HH molecules in the ordered state suffer a large distortion degree of the backbone thiophenes out of coplanarity. However, as for the PBTTPD molecules, the fact that a large steric hindrance from the TPD groups, these PBTTPD-M and PBTTPD-S polymer chains exhibit a disordered state. Hence, the main chains don’t intend to preserve a coplanar conformation as the P3HT molecules. The resultant UV-vis absorption spectra of P3DT-HT and P3DT-HH show one peak in the 200nm~800nm range, and the P3DT-HT exhibited absorption maximums at much longer wavelengths than those for P3DT-HH in the ordered state. When the P3DT molecules are grafted the accepter group (TPD) along the main-chains, the PBTTPD-M exhibits the same absorption features and shows one peak in the 300nm~750nm range. Conversely, when the P3DT molecules are grafted the accepter group (TPD) along the side-chains, the PBTTPD-S exhibits the shoulder absorption peaks at 300nm~700nm. These absorption results are strongly correlated with the conformation behavior of the accepter group along the side chains or main chains.
These results demonstrated the fact that when the P3DT molecules are modified with a conjugated accepter group (TPD) along the main-chains, the overall absorption spectrum becomes broader, in particular the total conjugated extension would be increased; the P3DT molecules are modified with a conjugated accepter group (TPD) along the side-chains, the overall absorption spectrum becomes broader, in particular a lower wavelength regime is significantly increased. And, the PBTTPD-M (HT and HH) exhibited absorption maximums at much longer wavelengths than those for the PBTTPD-S (HT and HH) both in the ordered state. Our simulated results for P3DT-HT and PBTTPD-M-HT in the ordered states have been shown in good agreement with the experimental results.

並列關鍵字

PBTTPD ； Donor-accepter pairs ； Optoelectronic properties

參考文獻

[10] Chen TA, Wu X, Rieke RD. J Am Chem Soc 1995;117(1):233-244.

[25] Liang Y, Yu L, Acc Chem Res 2010;43(9):1227-1236.

[33] Berrouard P, Najari A, Pron A, Gendron D, Morin PO, Pouliot JR, Veilleux J, Leclerc M, Angew. Chem Int Ed 2012;124(9):2110 –2113.

[38] Pron A, Berrouard P, Leclerc M, Macromol Chem Phys 2013;214(1):7−16.

[48] Sahu D, Padhy H, Patra D, Huang J, Chu C, Lin HC, J Polym Sci Part A N Polym Chem 2010; 48(24):5812–5823.