异代酯基枝状分子表面组装及结构转化机理的STM研究

利用扫描隧道显微技术(STM)研究了3种异代酯基Janus枝状分子(G1G2COOCH3, G0G3COOCH3, G1G3COOCH3)在高定向裂解石墨(HOPG)表面的组装结构. 室温下, G1G2COOCH3, G0G3COOCH3和G1G3COOCH3分别在表面形成有序、局部有序及无序结构. 将样品加热至60~80 ℃后, 表面无序结构可以转化为有序的二聚体密堆积结构. 实验结果表明, 随着枝状分子代数的增加, 分子之间及分子与基底之间作用力增强, 室温下分子组装行为更依赖于分子吸附动力学过程, 组装结构趋于无序化, 而加热可以增强枝状分子在表面的活动性, 调整分子的位置关系, 使表面无序结构转化为热力学稳定的有序二聚体密堆积组装结构.

Self-assembled Structures and Structural Transition of Dimethyl Isophthalate-Functionalized Janus Dendrimers on HOPG Investigated with STM

Self-assembled structures of three dimethyl isophthalate-functionalized Janus dendrimers G_1G_2COOCH_3, G_0G_3COOCH_3, and G_1G_3COOCH_3 were investigated with scanning tunneling microscopy(STM) on HOPG. It was found that G_1G_2COOCH_3, G_0G_3COOCH_3, G_1G_3COOCH_3 assembled into ordered,partial ordered, and disordered structures, respectively. After heated to 60-80 ℃, regular dendrimer dimers could be found on HOPG, resulting in close-packed ordered structures instead of the previous disordered structures. The results show that with the increase of the molecule generation, molecules are bound down onto surface due to the enhanced intermolecular and molecule-substrate interactions. The self-assembly is dependent on the dynamic process, leading to disordered structures. However, when heated, the mobility of dendrimer molecules on surface could be improved. Structural transformation from disordered structures to thermodynamically stable dimeric structures could be observed by STM on G_0G_3COOCH_3 and G_1G_3COOCH_3 adlayers.