The Assembly And Reaction Of Aromatic Carboxylic Acid Molecule On Metal And Carburization Surface

In recent years,surface chemistry building new functional nanomaterials has become a research hotspot in the field of science and technology.The carboxylic acid molecules not only can serve as both donors and receptors of hydrogen bonds to drive themselves to form various novel self-assembly structures on surface,but also carboxylic acid molecules can be widely used to produce late-model nanomaterials via versatile surface chemistry reaction,on account of only producing gaseous or volatile by-products on the surface.At present,the assembly structures formed by carboxylic acids on surface have been merely studied in morphology,but it remains sparse that the surface state electrons of metal is affected by assembly structure formed by hydrogen bonds of carboxyl.Besides the low yield,the decarboxylation coupling products are often poorly ordered.In addition,it is of great significance to study new catalysts about the carburized copper surface at the atomic/molecular scale.Hence,we not only can verify restriction of surface state electrons in the nanostructure adopting weak interaction with the substrate,and provide theoretical basis for designing,optimizing and synthesizing nanomaterials and new catalysts at the atomic/molecular scale by studying assembly and surface chemistry reaction of carboxylic acid on metal or carburized metal surface.To investigate the effect of nanostructure constructed by hydrogen bonds of carboxyl to surface state electrons of Au(111),combining with ultrahigh vacuum STM and DFT calculations,the molecular assembly structure of BCM on Au(111)substrate and corral effect of assembly structure to surface state electrons are studied.BCM molecules assemble gradually long-range orderly and twodimensional network structure via double-hydrogen bond of carboxyl through annealing the Au(111)sample deposited BCM at different temperature.The surface state of substrate confined to nanopore is directly image with STM for the first time at room temperature(RT).The bright ring is presented in nanopore.It has been confirmed that the bright ring in nanopore is the second eigenstate of surface state electrons,rather than molecular fragments,rotational molecule or state density of molecular skeleton,through theoretical calculation and in situ continuous scanning experiment.That bright ring in nanopore becomes more depression with scanning current growing larger and disappears with scanning bias decreasing shows surface state electrons of Au(111)directly imaged via STM is influenced by scanning current or scanning bias.Considering that it is difficult to produce chemical reaction of carboxylic acid on Au(111),the assembly and decarboxylation-cyclization reaction(DCR)of BCM on Cu(111)surface which show stronger reduction-oxidation ability are studied via STM,infrared reflection-absorption spectroscopy(IRAS)and DFT.At RT,BCM molecules assemble well-organized ‘zipper’ structure(named Z1)via intermolecular hydrogen bonding on Cu(111)with strong interaction between O of maleimido and its underlying Cu.The orderly ‘zipper’ structure gradually transforms into longrange orderly ‘flower’ structure by annealling at high temperature.It has been confirmed that BCM molecules form 6-PM-Cu structure via intermolecular DCR on surface confirmed by both IRAS and DFT calculations.A high-yield,long-range ordered on-surface synthesis of a large organic compound based on decarboxylation cyclization has been achieved by a designed ‘smart’ precursor.A ‘lock-to-unlock’variation of the molecule is realized upon the reaction.The molecular locking adsorption is indispensible for maintaining the molecules on the surface sufficiently long to increase the reaction yield at hihg temperature;the subsequent unlocking provides fair mobility for the cyclization and assembly of reacted species.And thanks to the steric hindrance of its maleimide group,preferential selection on the cyclization form is realized,where the chain structure is inhibited.The locking/unlocking of molecules is associated with intramolecular electron redistribution,opening up a promising route for on-surface synthesis involving high energy barriers.Combining with STM,XPS and DFT calculation,the local charge catalyzes replacement reaction between Cu and hydrogen of carboxylic acid(CA)group on carburized Cu(111)at the atomic/molecular scale is studied for the first time.Using chemical vapor deposition(CVD)method,we have confirmed that each surface Cu atom is found to be positively charged up to 0.30 e by the participation of subsurface C in Cu(111)through experiments and theoretical calculations.Then replacement reaction is accomplished via crucial deprotonation of CA group on BCM,which is catalyzed by surface charge,and O atom of deprotonated CA capturing Cu adatom,to form orderly ‘zipper’ structure(named Z2).The detailed DFT calculation has verified that surface charge lowers the deprotonation barrier by0.11 e V for each CA group,and converts the non-spontaneous reaction into spontaneous reaction.The deprotonation reaction rate constant increases by 100 times on carburized Cu(111)than that on pristine Cu(111)at room temperature.Such locally charged transition metal surfaces therefore hold great promise for onsurface synthesis and highly-selective catalysis.