Division of Molecular Imaging and Photonics, Department of Chemistry, KU Leuven-University of Leuven, Leuven, Belgium.
Phys Chem Chem Phys. 2013 Aug 14;15(30):12495-503. doi: 10.1039/c3cp51074c.
Understanding and controlling the structural polymorphism in self-assembled networks of functional molecules merit special attention. In this contribution, we describe the concentration controlled structural evolution in self-assembled monolayers of a large triangular discotic macrocycle at the liquid-solid interface. Scanning tunneling microscopy (STM) reveals that the adlayers formed by an alkoxy substituted cyclo-tris(7,9-triphenylenylene) macrocycle exhibit concentration dependent 2D phase behavior at the 1,2,4-trichlorobenzene/HOPG interface. The self-assembled network evolves from high-density linear packing which is formed at relatively high concentrations to a low-density porous pattern at lower concentrations. A trimeric hexagonal phase exists at intermediate concentrations examined. The transformation of the trimeric hexagonal phase to the linear phase could be monitored by recording time-dependent STM images. The self-assembly behavior is affected significantly by the choice of the organic solvent where an amorphous network is formed along with high-density linear packing at the 1-phenyloctane/HOPG interface. The results presented here provide detailed insight into the polymorphism phenomenon exhibited by an organic semiconductor and furnish general guidelines to control the morphology of thin films of such technologically important materials.
理解和控制功能分子自组装网络中的结构多态性值得特别关注。在本研究中，我们描述了在液相-固相间，大三角碟状大环分子的自组装单层中，浓度控制的结构演变。扫描隧道显微镜（STM）揭示了烷氧基取代的环三（7,9-二苯基芴）大环在 1,2,4-三氯苯/HOPG 界面上形成的吸附层表现出浓度依赖性的二维相行为。自组装网络从相对较高浓度下形成的高密度线性堆积转变为较低浓度下的低密度多孔模式。在中间浓度下存在三聚体六方相。通过记录时变 STM 图像可以监测三聚体六方相到线性相的转变。自组装行为受到有机溶剂选择的显著影响，在 1-苯基辛烷/HOPG 界面上形成了无定形网络以及高密度线性堆积。这里呈现的结果为有机半导体表现出的多晶现象提供了详细的见解，并为控制此类技术重要材料的薄膜形态提供了一般性指导。
