Chirality Recognition And Chirality Synthesis On Metal Surfaces

On-surface chirality recognition and synthesis play a pivotal role in a great number of technological applications ranging from non-linear optical devices,biosensors,enantioselective catalysis to chirality separations.With the development of surface science,ultra-high-vacuum scanning tunneling microscopy(UHV-STM)has proven to be an efficient method for the investigation of chirality recognition and synthesis as well as the underlying formation mechanism on solid surfaces,which benefits from its superiority of real-time,real-space,and atomic-scale resolution imaging.In this thesis,by the combination of UHV-STM imaging and density functional theory(DFT)calculations,we investigated the chirality recognition and synthesis of organic molecules on metal surfaces,and furthermore the roles of substrates and extrinsic atoms in the process of chiral recognition and synthesis are discussed in detail to get a deep understanding on the mechanisims.Understanding the mechanisms of molecular chirality generation,transfer and amplification is a fundamental basis for the precise construction of surface chiral architectures.We investigate the chirality recognition of a prochiral molecule,named BNOL,on different metal surfaces to explore the influence of substrates and extrinsic atoms on the chirality recognition and self-assembly behavior.On the reconstructed Au(111)surface,BNOL preferentially self-assembles into supramolecular chiral stripes through short-range chirality recognition in the FCC and HCP regions,and further the chirality transfer between neighboring chiral stripes is successfully achieved through long-range chirality recognition.However,on the unreconstructed Ag(111)surface,BNOL can only transfer its chirality through short-range chirality recognition.The key to achieving such long-range chirality recognition is the herringbone reconstruction-induced accumulation of dipoles at the edge of the chiral stripes,and the neighboring stripes are therefore forced to adopt the same chirality to create the opposite edged dipoles to neutralize the neighbored dipole moments.In contrast to short-range chirality recognition,long-range chirality recognition can span across potential surface defects to a certain extent,which endows self-assembled structures great properties of error-tolerance and promotes the formation of large-area homochiral structures.Besides,the introduction of bromine atoms on Ag(111)and further changing the ratio of BNOL/bromine atoms result in distinct chirality recognition and self-assembly behavior possibly due to the change of the adsorption site of bromine atoms and its atomic density on Ag(111).These findings provide new insights for chirality recognition as well as new approaches to construct large-area homochiral nanostructures and precisely control chirality recognition and self-assembly structures.Compared with non-covalent chiral self-assembly structures,covalent chiral architectures formed by on-surface reactions show higher chemical and thermal stability.In addition,the CH activation reaction is an ideal way for chirality synthesis because of its excellent characteristics of low by-product outcome,clean and high efficiency as compared with the CBr activation reaction.We selecte TFPB molecule as the precursor containing aldehyde groups and investigate its on-surface reaction on different substrates,aiming to design a clean and efficient model system for on-surface chirality synthesis.We find that on Ag(111),TFPB forms chiral dimer products through C-H activation of aldehyde groups and subsequent C-C coupling while it do not react after annealing on Au(111).After the introduction of iron atoms,the ordered structures are not be observed on Ag(111)due to the competition between the intrinsic silver atoms and extrinsic iron atoms.This is in stark contrast to the results for Au(111)where the formation of large-area chiral dimer products is achieved by the precise coordination of iron atoms with oxygen atoms,which promotes the C-H bond activation of aldehyde groups.These findings provide a new channel for the precise synthesis of surface chiral covalent products,which is of instructive significance for the further development of green and efficient surface chemical reaction systems.