Investigating Surface Reactions And Chiral Nanostructures Of Functionalized Biphenyl Molecules Via Scanning Tunneling Microscopy And Synchrotron Radiation Photoelectron Spectroscopy

Materials,energy,and information are the three pillars of human society development.Synthesizing new materials is of great importance to enhance people’s life quality.The synthesis of materials has been typically carried out by solution reactions.Solution reactions have disadvantages such as harsh reaction conditions and tedious product purification.As a complement to solution reactions,surface reactions have developed rapidly around last decade.In surface reactions,under the stimuli of light and heat,reactive precursor molecules on a solid surface(mostly metals)are activated,followed by migrating and reacting to form functional nanostructures.In contrast to solution reactions,substrates for surface reactions can catalyze surface reactions with confining and templating effects on surface reactions.The adsorbatesubstrate interaction contributes to the stable presence of highly reactive species like radicals.So far,a wide variety of nanostructures have been synthesized on solid surfaces via various surface reactions.The precursor molecules used for surface reactions usually contain functional groups.Therefore,the surface reactions of precursor molecules are typically accompanied by the generation of supramolecular self-assembled nanostructures,of which chiral lattices are very interesting forms of assembly.The study of twodimensional chiral supramolecular nanostructures possesses unparalleled advantages.With the help of advanced surface analysis,phenomena such as chiral recognition,transfer and amplification on solid surfaces can be elucidated.In particular,when reactive precursor molecules are used to construct chiral nanostructures,in addition to intact molecules,activated/reacted molecules can also form chiral nanostructures.This facilitates(1)the construction of multiple chiral nanostructures and(2)the understanding of phenomena such as chiral recognition and separation.To accomplish this,the choice of suitable precursor molecules is the key.The common backbones of precursor molecules are polyphenyl,tetraphenyl,aromatic rings,etc.Polyphenyl-like molecules are the most widely used molecular backbones,while biphenyl is the simplest polyphenyl-like molecule.Functionalized biphenyl molecules have a large family and are therefore ideal precursors.Studying the reactions of functionalized biphenyl molecules on surfaces and the accompanying nanostructures,especially chiral nanostructures,is an important guide for the construction of complex functional nanosystems.In this regard,in this dissertation,samples were prepared using molecular beam epitaxy(MBE)growth technique;the reactions and accompanying chiral nanostructures of functionalized biphenyl molecules on solid surfaces were investigated using scanning tunneling microscopy(STM)and synchrotron radiation photoelectron spectroscopy(SRPES),partially combined with low-energy electron diffraction(LEED)and density functional theory(DFT)calculations.On the one hand,we followed the reaction pathways of these molecules on specific surfaces.On the other hand,we prepared a variety of chiral nanostructures and elaborated the driving forces and chiral origins for the formation of chiral nanostructures.The main studies of the paper are as follows:(1)Different oxygen reconstructed surfaces were prepared controllably on Cu(110)and the adsorption/reaction behaviors of 4-ethynyl-1,1’-biphenyl molecules(EBPs)on them were investigated.On Cu-O nanotemplates,dehydrogenated EBPs prefer to adsorb in the Cu region and form V-shaped dimers in large proportions.On the Cu(110)(2×1)O surface,unreacted EBPs self-assemble into large and well-ordered regions where noncovalent EBP dimers are located in the Cu-O interchain grooves.On Cu(110)-c(6×2)O,the noncovalent EBP dimers are confined by the super copper atoms.In addition,we found for the first time a Cu(110)-p(2×3)O surface,which,however,exhibits no affinity towards EBPs.(2)A series of large-area ordered chiral nanoporous networks consisting of deprotonated dehydro-4,4’-dihydroxybiphenyl(DHBP)were successfully constructed on the Ag(100)surface by stepwise annealing.The vertices in the network contain chiral dimeric,trimeric,and tetrameric vertices stabilized through O…H hydrogen bonds and O-Ag coordination.Different chiral vertices and combination modes of these chiral vertices give rise to chiral nanopores with different shapes and sizes,which have a modulating effect on the number and morphology of their inner Ag adatoms.There is a strict chiral correlation between nanopores and their vertices.For a pair of nanopore enantiomers,vertices at the mirror symmetry position have the same type but opposite chirality.(3)Large-area ordered chiral self-assemblies containing surface-stabilized radicals were controllably constructed by depositing 4-bromoethynyl-biphenyl(BEBP)on the Ag(100)surface held at different temperatures to induce surface reactions.Chiral islands composed of pure surface-stabilized radicals are generated at low surface temperature.As the surface temperature increases during precursor deposition,organometallic(OM)dimers appear and their proportion increases at the expense of that of surface-stabilized radicals.Hierarchical chirality was found in all chiral selfassemblies.These structures are generated under kinetic control.Theoretical calculations unravel that these radicals are stabilized by binding to surface Ag atoms.The interactions between phenyl H and alkynyl π system should be the major driving force for network formation.(4)The reaction pathway and accompanying(chiral)nanostructures of the cyanomodified halogenated aromatic,4’-bromo-4-cyanobiphenyl(BCBP),on Ag(111)/Ag(100)surfaces were investigated.On Ag(111),C-Br is gradually activated and the proportion of organometallic(OM)dimers gradually increases,accompanied by the formation of various surface self-assembled structures.Further annealing of the structures composed of pure OM dimers fails to trigger the C-C coupling reaction.Instead,the disintegration of OM dimers and the activation of cyano ortho C-H occur,resulting in the prochiral OM multimers.The generation of chiral OM structures and the blocking of the OM to covalent transition are also observed on Ag(100).