Impact of Nitrogen Substitution and Molecular Orientation on the Energy-Level Alignment of Heteroacene Films

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• 作者：Qian Xin ; Steffen Duhm ; Shunsuke Hosoumi ; Nobuo Ueno ; Xu-tang Tao ; Satoshi Kera
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：August 11, 2011
• 年：2011
• 卷：115
• 期：31
• 页码：15502-15508
• 全文大小：966K
• 年卷期：v.115,no.31(August 11, 2011)
• ISSN：1932-7455

文摘

The impact of imine nitrogen (鈺怤鈥? substitution in hydrocarbon oligoacenes on the charge-transport type has been carefully probed. A N-heteroacene containing one 鈺怤鈥?and 7-fused rings, dianthrano [1,2-a:1鈥?2鈥?j]pyridine (DAP), has been synthesized as a model molecule for the study. The electronic structure, energy-level alignment (ELA), and the molecular orientation of the molecule on two prototypical substrates, namely, highly oriented pyrolytic graphite (HOPG) and Ag(111), have been investigated using angle-resolved ultraviolet photoelectron spectroscopy. Combining crystal structure, optical property and electronic structure investigations, our results indicate that by introduction of only one 鈺怤鈥?into a large oligoacene, the ELA can be effectively tuned and a potential of n-type conductivity can be realized. Furthermore, the permanent electric dipole induced by the intramolecular polar bonds (C鈥擭 and C鈥擧) allows tuning the ELA by altering the molecular orientation. Tilted molecular orientations can impose smaller electron injection barriers and ionization energies to DAP thin films than a flat-lying orientation.