2D Self-assembly Of Functional Organic Molecules And Fabrication Of Its Host-guest Structures

Diaminotriazine,triphenylamine and macrocyclic derivatives are functional molecules,which are widely used to the fields of liquid crystals,optoelectronic devices,solar cells and molecular recognition.The properties of materials depend on the stack modes of molecules.Therefore,fabricating materials with special functions set about studying its single molecular arrangement,and then regulated the macroscopic properties of materials.In the field of twodimensional(2D)interface organic molecular self-assembly,the rational design of building blocks and the control of external conditions are important means to fabricate complex structure to apply in functional devices.In this paper,three molecules with different molecular structures and photoelectric properties were designed and systematically explored the molecular side chain length,molecular structure and molecular structure by combing with scanning tunneling microscopy(STM)and density functional theory(DFT)calculation.In order to reveal the mechanism of the weak interaction between molecules and the change of external factors on the molecular assembly structure,the concentration effect of solution and other factors regulate the fabrication of the molecular assembly structure and its host-guest structure at the solid/liquid interface.The main contents and innovative results of this dissertation are summarized as follows:(1)The self-assembly behaviors of diaminotriazine derivative(2TDT-10)self-assembly at2 D liquid/graphite interface use short chain or long chain solvents changing different concentrations,respectively.Short chain solvents include 1-octanoic acid and 1-phenyloctane,and long chain solvents include n-tridecane and n-tetradecane.By adjusting the concentration of each solution,we found that only the four leaved-I structure was observed in the short chain solvent.In long-chain solvents,we observed not only the four leaved-I self-assembly structure,but also the new four leaved-II structure(only in n-tridecane solvents),and the chiral Kagoméstructure were observed at low concentration 2TDT-10/n-tridecane and n-tetradecane solvents.The experimental results show that the four leaved-I structure is a close packed structure without solvent co-adsorption.The formation of four leaved-II structure and Kagomé is due to the co-adsorption of three and five long-chain solvent molecules,respectively.In this process,the solvent molecules act as templates to induce the formation of Kagomé structure.However,the Kagomé structure is an ideal cavity for capturing guest molecules,so we introduced the guest molecule coronene(COR)into the cavities of Kagomé structure to form the co-assembly structure.This result indicates that the adsorption capacity of COR on graphite substrate is stronger than that of solvent molecules,and the Kagomé structure has the capacity of selective adsorption for COR.(2)The self-assembly behaviors of diaminotriazine derivatives(2TDT-n,n = 10,12,16 and 18)at 1-octanoic acid/graphite interface by adjusting the length of alkyloxy chains.The results show that the structure of 2TDT-10 only form four leaved-I at different solution concentrations of 1-octanoic acid.There are three nanostructures in 2TDT-12,which are fragment shaped,linear shaped,and flower shaped,respectively.2TDT-16 and 18 mainly formed linear structure.Through analysing the self-assembly structure and constructing the model,the results show that with the increasing of the alkoxy chain length,the bithiophenes group in the molecular backbone of diaminotriazine derivatives will gradually change from cis to trans conformer.With the increasing of side chains,the self-assembly structure of molecules will gradually change from other structures to linear structures.It is suggested that the configuration of molecular backbone(cis and trans isomer)can be controlled by adjusting the length of alkyloxy chain.(3)In view of the application of push-pull dye molecules in the field of solar cell,the selfassembly structure of triphenylamine derivative(NNDP)molecule was investigated at the 1-octanoic acid/graphite interface.The chemical structure of NNDP is complex,including the head of indanone,the main chain of bithiophene and the tail of triphenylamine modified by two carboxyl groups.In the self-assembly structure,the molecule adopts a bent "L" shape to form a unique triangular trimer.As a building block,these triangular trimers successfully form three kinds of complex 2D Kagomé(α,β and γ)nanopore structures through different arrangements.Among them,the structures of Kagomé-α and Kagomé-β were formed at low and high concentrations,respectively.Kagomé-γ structure needs to be induced by particular guest molecules.For chiral Kagomé-α nanostructures,we introduced new guest molecules such as pyrene,triphenylene and zinc phthalocyanine(Zn Pc),and formed its host-guest co-assembly structures.In this process,we successfully observed the growth kinetics of NNDP and the adsorption dynamic of the guest molecule(Zn Pc)by adjusting the concentration of the guest molecule.In addition,we also found that the smaller guest molecules can be replaced slowly with the larger guest molecules and the adsorption ratio in the cavity can be controled by adjusting the concentration of COR.(4)The self-assembly behaviors of BDT at the 1-octanoic acid or 1-phenyloctane/ graphite interface and its selective adsorption behavior for small guest molecules were investigated.The results show that the macrocyclic molecules are arranged in regular and uniform pattern on the surface of HOPG.No matter in 1-octanoic acid or 1-phenyloctane solvent,the alkyl chains of BDT molecules will extend along different axials of graphite lattices without obvious domain boundaries,resulting in several domain distributions.Next,some guest molecules such as triphenylene,pyrene and 1,10-phenanthroline-5-amino were trapped by the cavites of macrocyclic molecules on the surface of HOPG.The experimental results show that the molecules such as triphenylene,pyrene and 1,10-phenanthroline-5-amino can be successfully trapped in the cavity of BDT macrocyclic molecules due to their proper size and shape.After the experiment of host-guest co-assembly,the obvious characters were observed.Firstly,the shape of macrocycles changed from ellipse to circle.Secondly,bright spots were observed in the cavity of each ring.The results will help us to understand the host-guest self-assembly more deeply and provide a theoretical basis for the preparation of optoelectronic materials with excellent properties.The host-guest nanostructures of optoelectronic molecules achieve the phase separation of guest molecules,which form P–N junction at the nanoscale.This is of great significance to the construction of optoelectronic materials.