STM Investigation Of Self-Assembled Structures Of Helicene Compounds On HOPG Surface

ABSTRACT:Helicene compounds have caused widespread concern in the academe because of their outstanding optical and electrical properties.In this work,we investigate the assembling of thiophene-based helicenes in two-dimensional(2D)porous network by using scanning tunneling microscopy(STM)in combination with density functional theory calculation The main work of this thesis are as follows:(1)The self-assembly behavior of double helicene(X1)and(TMS)2-[7]helicene(C1)in templates on the HOPG surface.Herein,scanning tunneling microscopy(STM)is employed to investigate the nanostructures.During the experiment,we observed that both X1 and C1 could be immobilized into the host molecular frameworks fabricated by TCDB.Moreover,when Cl/TCDB system was deposited on graphite surface,two kinks of well-ordered arrays could be observed,and only one kind of conformation could be obtained after depositing the X1/TCDB system onto the HOPG surface.However,we can not get the STM results of X1 and C1 without nano template,the current findings provide a new approach towards the formation of helicene compounds.(2)The self-assembly behavior of cyclooctatetrathiophenes(COTh)and ?,?,?,a-tetraaryl-tetithiophene octaheterocyclic(COThP)in templates on the HOPG surface.Two cyclic oligothiophene compounds with three-dimensional saddle-type structures have been successfully synthesized.Both COTh and COThP are difficult to adsorb on the graphite because of their stereoscopic configuration.In order to get their STM image successfully,TCDB is employed to build the host molecular frameworks to immobilize the guest molecular.According to the experimental results,the well-ordered arrays of COTh/TCDB system and COThP/TCDB system could be observed.The results reveal that host-guest assembly system take a important role in the study of thiophene-based helicenes assembly behaviour,which can benefit the investigation of the formation of host-guest system at interfaces.