Seeing Modulability Self-Assembled Monolayers of π-Conjugated Perylene Derivatives by Scanning Tunneling Microscopy

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• 作者：Xiao-Ping Liu ; Ling-Wei Xue ; Qian Wei ; Minghui Liang ; Ke Deng ; Zhan-Jun Zhang ; Peng Jiang
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：August 25, 2016
• 年：2016
• 卷：120
• 期：33
• 页码：18607-18615
• 全文大小：645K
• 年卷期：0
• ISSN：1932-7455

文摘

Three kinds of new large π-conjugated perylene-bithiophene-perylene (PBTP)-based organic functional derivative materials, i.e., PBTP-bisimide, PBTP-bisimide-C₈, and PBTP-ester, have been synthesized and imaged on highly oriented pyrolytic graphite (HOPG) by scanning tunneling microscopy (STM) under ambient conditions. These molecules with a common PBTP core and various substituents show completely different ordered self-assembly patterns on the HOPG depending on the core symmetry matching with the substrate surface lattice, alkyl substituent structure, and alkyl-chain number directly linked to suitable sites on the core. Four dimethylaminopropyl substituents at N sites on the PBTP-bisimide molecule lead to an ordered line-like molecule arrangement with a same molecule orientation. Increase of the branched alkyl-chain to C₈ for PBTP-bisimide-C₈ does not change the line-like molecule arrangement and orientation in the two-dimensional (2D) ordered assembly structure, just stretching intercore distance in the same row. With the increase of the substituent number at suitable positions on the main PBTP core, for example, the PBTP-ester molecule with eight butyl-ester substituents taking 3, 4, 9, and 10 carbon sites of two perylene motifs, a 2D ordered hexagonal porous molecule network structure is formed because the steric hindrance and the conformational flexibility of the more butyl-ether chains can drive the molecular main backbone to rotate to fit the graphite lattice. This new finding clearly shows that the orientation and position of the large coplanar π-conjugated PBTP cores adsorbed on HOPG can be precisely modulated from lamella to six-membered hexagonal structure through changing the number and noncovalent interaction directions of alkyl-chain substituents. Density functional theory (DFT) calculations have been utilized to reveal the formation mechanism of the molecular nanoarrays. The side-chain design for various self-assembled structures of the large π-conjugated molecules on HOPG provides a new route toward constructing three-dimensional novel PBTP-based ordered molecular film, and further optimizing the electrical transport property of the film for exploiting advanced organic film field effect transistors.