非平面多環芳烴作為場效電晶體材料之應用- 結構性質關係研究

Contorted Polyaromatics as Field-Effect Transistor Materials- a Structure Property Correlation Study

黃鼎棋(Ding-Chi Huang)

指導教授 ： 陶雨臺

國立清華大學/理學院/化學系/博士(2015年)

摘要

在有機電子學的有機半導體分子設計研究中，分子結構與其載子移動率之間的相關性是一個重要的課題。相對於其他方式的分子堆疊，面對面的軌域重疊因其有可能獲得較大的電子耦合，進而有利於載子傳輸，所以獲得青睞。具有面對面結晶排列的分子目前已在有機半導體中展現其優越性。於此類化合物，非平面的多環芳烴被視為一有前瞻性的材料，因該類分子很容易得到面對面排列。
本論文報導兩系列的非平面多環芳烴之合成與其鑑定。以這些化合物的單晶製備成單晶場效電晶體並量測其特性。論文中針對對於晶體結構排列，理論計算所得的電子耦合與實際單晶場效電晶體的載子移動率之關聯性進行討論。
第一個系列是四苯駢駢苯家族，此系列化合物具有不同的合環共軛長度。藉由X光繞線分析顯示，這些分子皆表現出非平面型結構，除了一個從意外的環戊稠環反應中所得到的平面分子。根據不同的共軛長度，非平面型未取代四苯駢駢苯化合物之結晶表現出部份或是完美面對面排列。甲基取代的四苯駢萘衍生物則呈現π平面位移排列。平面型環化四甲基四苯駢駢六苯之結晶行為是往一維方向位移的π 堆積。在這類化合物中，四苯駢駢八苯的計算電子耦合值為最高，可達到131 meV;然而在元件表現上，四苯駢駢四苯展現了最高的載子移動率，為0.8 cm2 V-1 s-1。實驗結果與其理論計算數據進行了對照。
本文另一系列為在1,2,3,6,7,8位置上的不對稱取代基之非平面四苯駢蒄衍生物之合成與其特性報導。藉由不對稱取代，分子內生成一偶極矩，此偶極作用力影響了晶體排列。此系列化合物之晶體皆為針狀，也並應用於單晶場效電晶體。氟取代的不對稱四苯駢蒄衍生物的晶體排列有兩種形式，一種是為反向平行且同面成對，另一種則是稍微位移的π- 堆積。而體積較大的烷基取代之四苯駢蒄表現出歪斜且明顯的π-堆疊位移。由於六氟取代的四苯駢蒄之晶體中分子上下堆疊，在長軸方向雖然位移甚大，在短軸方向位移卻甚小，仍可得到較大的電子耦合，所以在單晶場效電晶體的元件表現中，該化合物表現出最佳的電洞移動率，與理論計算結果相符。

關鍵字

有機場效電晶體 ； 有機單晶場效電晶體 ； 四苯駢駢苯 ； 四苯駢蒄

並列摘要

The correlation between the molecular structures and charge carrier mobility is a key issue in the design of organic semiconductors to be used in organic electronics. The face-to-face π-orbital overlap is envisioned to be favored for charge transport because of higher electronic coupling possible compare to other relative dispositions. Molecules which have face-to-face crystal stacking have shown their superiority in organic semiconductors. Among these compounds, a promising candidate is contorted polyaromatic, because it has a high tendency to give face-to-face packing. In this thesis, two series of contorted polyaromatics were synthesized and characterized. Single-crystal field-effect transistors based on these molecules were fabricated and performance measured. A systematic comparison of the crystal packing and the calculated electronic couplings with the measured SCFET mobility was presented.
The first family was the contorted tetrabenzoacenes with extended conjugation. The contorted molecular structures were clearly established except for a planar closed-ring compound which was obtained from an unexpected cyclopenta-ring fused reaction. Unsubstituted tetrabenzoacenes showed a partial or perfect face-to-face packing depending on their conjugated length. Methyl substituted tetrabenzonaphthalene derivatives gave shifted π-stacking. Planar cyclized tetramethyl tetrabenzohexacene exhibited one-dimension slipped π-stacking. Theoretical calculation was carried out based on the crystal structure. Among these, the electronic coupling of tetrabenzooctacene was the highest (131 meV). Nevertheless, tetrabenzotetracene exhibited the highest measured mobility, approaching 0.8 cm2 V-1 s-1. A comparison of the experimental measurements and the theoretical calculation is presented.
Another series of contorted tetrabenzo[a,d,j,m]coronene (TBC) derivatives with substituents at 1-, 2-, 3-, 6-, 7-, 8-positions were designed, synthesized, and characterized. The unsymmetrical substitution introduced dipole moment to the molecule which also affects the crystal packing. Needle-like single crystals were used for crystal structure analyses as well as the SCFET device fabrication. Derivatives with fluoro-containing substituents exhibit antiparallel cofacial or slightly shifted - stacking, whereas those with bulky alkyl substituents show skewed and more significantly shifted - stacking. The hexa-fluorinated TBC crystal showed significant shift along long molecular axis but rather small shift in the short axis. A much larger electronic coupling and thus a highest hole-mobility was achieved, in agreement with theoretical calculation.

並列關鍵字

OFET ； single crystal field-effect transistor ； tetrabenzoacene ； tetrabenzocoronene

參考文獻

52. Li, Y.; Wang, C.; Li, C.; Di Motta, S.; Negri, F.; Wang, Z. Org. Lett. 2012, 14, 5278-5281.

88. Janietz, S.; Bradley, D. D. C.; Grell, M.; Giebler, C.; Inbasekaran, M.; Woo, E. P. Appl. Phys. Lett. 1998, 73, 2453-2455.

57. Hiszpanski, A. M.; Lee, S. S.; Wang, H.; Woll, A. R.; Nuckolls, C.; Loo, Y.-L. ACS Nano 2013, 7, 294-300.

94. Loo, Y. L.; Hiszpanski, A. M.; Kim, B.; Wei, S.; Chiu, C. Y.; Steigerwald, M. L.; Nuckolls, C. Org. Lett. 2010, 12, 4840-4843.

73. Mukherjee, A.; Pati, K.; Liu, R.-S. J. Org. Chem. 2009, 74, 6311-6314.