Theoretical Study On Host-guest Self-assembly Of BIC/nonanol+COR

Molecular self-assembly is a powerful "bottom-up" strategy for the nanofabrication of specific nanopatterns.Due to potential applications in separation techniques,molecular catalysis and molecular sensors,the host-guest self-assembly on solid surface has become a rapidly developing field.In order to effectively control the host-guest self-assembly to obtain the structure with specific performance,it is necessary to analyze the configuration,formation regularity and stability evolution of the surface host-guest self-assembly.To this end,this paper studied the molecular self-assembly configurations of 5-(benzyloxy)-isophthalic acid derivative(BIC)and coronene(COR)at the interface of nonanol(S/R-nonanol)/highly oriented pyrolytic graphite(HOPG)by using density functional theory(DFT),molecular mechanics(MM)and molecular dynamics(MD)simulations.We explored the effect of guest on structure rearrangement,the effect of alkyl chain length on chiral switching,the effect of solvent on chiral configuration and weak interactions in the host-guest self-assembly.Firstly,the effect of guest on structure rearrangement was studied by self-assembly system of BIC-C8/S-nonanol(+COR)on HOPG surface.DFT calculation was performed on the simplified fragment(benzoic acid/methanol)to obtain accurate structural parameters,and compared with the MM calculation results with different force fields,the cvff closest to the DFT calculation results was selected for MM and MD calculations in this paper.Combined with the simulation results of geometric configuration,energy,characteristic hydrogen bond parameters,size matching and surface density,it revealed that the self-assembled structure changed from honeycomb to starfish after adding the guest.The reason for the structural response rearrangement was that in order to match the size of the guest,the flexible host network rearranged to starfish and interacted with the guest,thereby fixing the COR molecule.Secondly,the effect of alkyl chain length on chiral switching was studied by the self-assembly system of BIC-C16/S-nonanol(+COR)on HOPG surface.The geometric configuration,adsorption energy,characteristic hydrogen bonding parameters and structural evolution of the system were simulated.The results showed that when the host molecule was BIC-C8,the homochirality was obtained both in the absence and the presence of COR.When the host molecule was BIC-C16,the homochirality was obtained in the absence of COR,and after the addition of COR,a racemic structure was formed.It was found that the chirality switch depended on the alkyl chain length.When the alkyl chain was shorter,the solvent formed hydrogen bonding with BIC in the absence and the presence of COR and a homochirality structure was formed.When the alkyl chain was longer,the solvent still participated in self-assembly.After the addition of COR,BIC alkyl chains were longer and interdigitated,there was no space to accommodate the solvent,thereby forming a racemic structure.Thirdly,the effect of the solvent on the chiral configuration was studied by the self-assembly system of BIC-Cn(n=8,16)/R-nonanol(+COR)on HOPG surface.By calculating the adsorption energy,characteristic hydrogen bonding parameters,structure evolution,it was revealed that solvents with different chiralities could induce different homochirality structures or globally racemic structures.If the solvent participated in self-assembly,it was mainly related to the steric hindrance effect between the substrate and the methyl group attached to chiral carbon of solvent.If the methyl group was upward relative to the substrate and steric hindrance,the steric hindrance was small.The hydrogen bonds were easily formed and the corresponding chiral structure tended to form.If the methyl group was downward relative to the substrate,the steric hindrance was large.It did not tend to form hydrogen bonds,and the corresponding chiral structure did not tend to form.If the solvent did not participate in self-assembly,it tended to form a global racemic structure.All the simulation results were compared with the experimental STM images to verify the reliability of the calculation and analysis.Finally,because the main structure of BIC is isophthalic acid(ISA),the weak interaction analysis focused on the self-assembly system of ISA(+COR)on HOPG surface.Based on the experimental STM image,accurate self-assembled atomic configurations were constructed by DFT calculation.After optimizing the structure,the STM image simulation was carried out,and it was found that the STM simulation images were consistent with the experimental results.The results of electron density difference analysis revealed that the weak interaction in the BIC/nonanol(+COR)self-assembly on HOPG surface included ?-? stacking effect and Van der Waals interaction in addition to hydrogen bonding.