Fabrication And Investigation Of Two Dimensional Supramolecular Self-assembly For Anthraquinone And Fluorenone Derivatives

Fabrication of complex two-dimensional（2D）self-assembly at the liquid/solid or on dry interface has attracted immense attention in the field of not only supramolecular chemistry but also interfacial science.A great deal of attempts focus on inducing structural diversity on substrate,which displays positive potentials on designing functional materials with novel physical and chemical properties.Therefore,efficient control over the transition between diverse structures is of increasing significance to explore.In this thesis,based on the anthraquinone and asymmetrically-substituted fluorenone derivatives,we systematically explore the 2D self-assembly which can be regulated by solvent effect,concentration effect,chain-length effect and alkyl chain number and position effect.We reveal the relationship between assembled nanostructures and different diving forces,such as hydrogen bonds,van der Waals interaction and dipolar interaction.The main work and innovative results are as follows:（1）Anthraquinone derivatives with different number of alkyl chain are explored at the 1-octanoic acid/HOPG interface.For the purpose of investigating how the molecular structure can affect the self-assembly process,we change the alkyl chain number,position and length.Based on this assumption,we use the mono-substituted molecuels of 1-HA–OC_n and 2-HA–OC_n（n=15,16）;bis-substituted molecules of 1,8-A–2OC_n,2,6-A–2OC_n,1,4-A–2OC_n and 1,5-A–2OC_n（n=15,16）;tri-substituted molecules of 1,2,4-A–3OC_n（n=15–18）.According to the packing mode of different molecuels in the adlayer,we found that the self-assembled nanostructures were directly related to the alkyl chain number,positon and length.The emergence of odd-even effect is an indication that one of the driving forces is van der Waals interaction,because the molecules in a row will change their packing into an appropriate direction to maximizing their interdigitation.Hydrogen bonds between adjacent anthraquinone cores are another driving force on stabilizing the self-assemblyed monolayer.In most cases,molecuels are packed into antiparallel pairs,which means that dipole–dipole interaction also plays significant role.Moreover,1,2,4-A–3OC_17,18 self-assembled into monolayers consist of both ordered and chaotic domains.This loss of regularity was attributed to the large number and long length of the side chains,for entropy reasons.（2）We use 2-HA–OC_n（n=12,14,16,18,20）derivatives to explore the structural transition control over chirality and achirality.Two interesting nanostructures extremely resemble Chinese knot and wheat were observed,thus they were denoted as Knot-like and Wheat-like patterns.Careful observation suggests that the Knot-like structure is chiral while the Wheat-like structure is achiral.Systematic analysis indicates that these two arrangements are mainly dominated by synergistic forces of dipole-dipole and hydrogen bonding interactions.To the best of our knowledge,the dipole induced chirality and achirality has been rarely reported,and the synergistic forces of dipole-dipole and hydrogen bonding interactions on dominating 2D assembly have never been proposed.In addition,structural transition between the Knot-like and Wheat-like configurations can be regulated by concentration and solvent as the alkyl chain length changes.Note that the phase transformation is in most cases incomplete.A summary of surface coverage for 2-HA–OC_n（n=12,14,16,18,20）molecules shows the general trend that Knot-like structure is preferred in polar solvent and under low concentration,while Wheat-like structure is opposite.Besides,2-HA–OC_n（n=11,13,15,17）molecules adopted Wheat-like′pattern which differs from the Wheat-like pattern in the relative orientation of adjacent ribbons,ascribing to minimum of steric repulsion between the interdigitated alkyl chains.（3）Chain-length effect is traditionally explored by gradually enlarging the side chain length by one carbon atom.Based on the fluorenone derivatives,aimed to inducing structural diversity,we use three new method on changing the alkyl chain length.Firstly,we use two kinds of side chains,and obtained three molecules of F–C₇C₇,F–C₁₄C₇ and F–C₁₄C₁₄.Secondly,via fixing one chain and prolonging the other chain by five carbon atoms(–C₅H₁₀–),we successfully obtained six molecules of F–C₁₅,F–C₁₅C₅,F–C₁₅C₁₀,F–C₁₅C₁₅ and F–C₁₅C₂₀.Thirdly,via modifying the two side chains in a certain molecule by the difference of one carbon atom and then gradually increasing the alkyl chain length,seven fluorenone derivatives(F-C_nC_n+1,n=11-17)were synthesized.These methods for changing the side chain have never been reorpted in the field of 2D self-assembly.At the 1-octanoic acid/HOPG interface,as the alkyl chain length changes,the self-assembly structure displays huge difference.A new phenomenon is that stable chiral structures were usually observed,which is different from the previous work in our group on symmetrically-substituted fluorenone derivatives.Thus,this is also a promotion in this fluorenone system.（4）By designing a fluorenone derivative of 2-heptyloxy-7-pentadecyloxy-9-fluorenone（HPF）,we obtained a surface-confined system that presented diverse nanostructures.The assembled networks for HPF were closely dependent on the solvent and concentration.At the liquid/solid interface,chiral Tetramer-S,Hexamer-S,Tetramer-linear structures,and achiral Irregular-linear,Random structures were recorded.On the dry surface,we observed chiral Octamer-S and achiral Alternate configurations.During the self-assembly process,the short and long alkyl chains for HPF showed selective identification,which contributed to the formation of S-like or anti-S-like tetramer,hexamer and octamer,resulting in chiral structures.The nanopatterns were stabilized under the driving forces of dipolar interaction,hydrogen bonds and van der Waals interaction.Moreover,we performed forcefield calculations in order to further understand the underlying mechanisms from the viewpoints of the force strength and their binding energies.（5）The self-assemblies of 2-decyloxy-7-pentadecyloxy-9-fluorenone（DPF）were characterized at the liquid/solid interface.Achiral Dimer and chiral S-like structures were observed in 1-octanoic acid.The solvent molecule took part in the self-assembly via forming COOH···O═C and COOH···COOH hydrogen bonds.When 1-phenyloctane and n-tetradecane were used as the solvents,DPF self-assembled into chiral Z-like structure,which were classified into Type I to IV according to the packing styles.For the purpose of exploring the effect of solvent and the competition between these three structures,we investigated the self-assemblies of DPF in mixed solvents and on dry surface.The results showed that S-like structure was preferred in mixed solvents,while the Z-like structure had priority when the function of solvent was excluded.To explore which structure is preferred during the self-assembly process,the common method is based on quanlitative analysis and calculation.Using mixing solvent to explore the competition between two structures is a method which is simple but visible.