調控單分子橋接系統之研究：以掃描穿隧顯微術之斷裂接合法測量直線型金屬串及金屬紫質之導電值

Tuning of Single Molecular Junctions: Conductance Measurements of Extended Metal-Atom Chains and Metalloporphyrins by STM Break Junction Method

呂浩誠(Hao-Cheng Lu)

指導教授 ： 陳俊顯

國立臺灣大學/理學院/化學研究所/博士(2012年)

https://doi.org/10.6342/NTU.2012.02310

摘要

架接於兩電極間的單分子，影響其導電值的因素來自於分子主體、分子與電極間的鍵結方式及分子軌域與電極間的能障。本論文以掃描穿隧顯微術之重複斷裂接合法(scanning tunneling microscopy break junction, STM BJ)量測分子導電值，目標分子為(1)直線型金屬串分子([MnL4(NCS)2], M = Ni2+, Co2+, Cr2+; n = 3, 5, 7; L = oligo-α-pyridylamido anions)及(2)紫質(bis-5,15-(3,5-di-tert-butylphenyl)- (10,20-di- pyridyl-porphyrin), DPDPyP)。利用電化學方法控制直線型金屬串分子的氧化還原態，以STM BJ測量分子中性態與第一個氧化態的導電值，顯示導電值趨勢與金屬核間的作用力有關。I(V)曲線經數據處理可得到轉變電壓(transition voltage, Vtrans)，說明金屬串分子越導電時可得到越小的Vtrans，間接瞭解分子軌域−電極間的能障與導電值的關係。此外，若將原型金屬串分子的多吡啶胺改變為具推拉電子基的橫向配位基，亦會達到調控分子串之導電值。
本論文也探討紫質的導電值，其中心金屬為鐵(III)、鈷(II)、鎳(II)、銅(II)、鋅(II)及free base。紫質主要具有兩組導電值，由分子長度與探針−表面間之距離，得到紫質在高導電值時以傾斜30度架接在兩電極間，而低導電值時紫質垂直於表面。由不具與電極鍵結的頭基的coronene及hexabenzocoronene平面高共軛分子仍可測得導電值，推論金屬紫質在高導電值時電子會直接由電極經過紫質本體到達另一端電極，高導電值的差異與中心金屬有關；低導電值時電子是以紫質外環作為傳遞路徑，與中心金屬無關。

關鍵字

分子導電值 ； 直線型金屬串分子 ； 紫質

並列摘要

The charge transport of single-molecule is dictated by the charge injection efficiency at the electrode-molecule contacts and through the molecule. Studied herein is to measure the conductance of (1) the extended metal-atom chains (EMACs, [MnL4(NCS)2], M = Ni2+, Co2+, and Cr2+; n = 3, 5, and 7; L = oligo-α-pyridylamido anions) and (2) metalloporphyrins (bis-5,15-(3,5-di-tert-butylphenyl)- (10,20-di-pyridyl) porphyrin, DPDPyP) by the technique of scanning tunneling microscopy break junction (STM BJ). The redox states of EMACs can be controlled electrochemically and the conductance can be measured. The conductance at the two states is qualitatively well correlated with the metal-metal interactions. Higher conductance of EMAC exhibits smaller transition voltage can realize the relationship between the energy gap and the conductance. In addition, the conductance of EMACs can be tuned by replacing the oligo-α-pyridylamido anions with electron-donating or electron- withdrawing ligands.
The DPDPyPs with the metal centers of Fe(III), Co(II), Ni(II), Cu(II), Zn(II), and free base show two conductance (HC and LC) regions. In comparison with the molecular length and the tip-electrode distance, DPDPyPs tilt 30o and 90o between two electrodes in the HC and LC region, respectively. The conductance of coronene and hexabenzocoronene without anchoring group can also be measured, suggesting that electrons can pass through the molecules. We propose that the electrons pass directly through the porphyrin rings in the HC region and along porphyrin rings in the LC region.

並列關鍵字

molecule conductance ； extended metal-atom chains ； porphyrins

參考文獻

(100)Wang, C.-C.; Lo, W.-C.; Chou, C.-C.; Lee, G.-H.; Chen, J.-M.; Peng, S.-M. Inorg. Chem. 1998, 37, 4059-4065.

(57) Wu, S.; Gonzalez, M. T.; Huber, R.; Grunder, S.; Mayor, M.; Schonenberger, C.; Calame, M. Nature Nanotechnology 2008, 3, 569-574.

(141)Jang, S.-Y.; Reddy, P.; Majumdar, A.; Segalman, R. A. Nano Lett. 2006, 6, 2362-2367.

(119)Lim, J. M.; Yoon, Z. S.; Shin, J.-Y.; Kim, K. S.; Yoon, M.-C.; Kim, D. Chem. Commun. 2009, 261-273.

(27) Zheng, Y. B.; Payton, J. L.; Chung, C.-H.; Liu, R.; Cheunkar, S.; Pathem, B. K.; Yang, Y.; Jensen, L.; Weiss, P. S. Nano Lett. 2011, 11, 3447-3452.