Synthesis And Spectral,Electrochemical,and Self-Assembly Properties Of A Novel Sulfur-fused Molecular Graphene With Highly Symmetrical Structure

Polycyclic aromatic hydrocarbon(PAH)molecules possessing a similar structure to that of the graphene has been widely applied in the field effect transistor,light-emitting diodes,solar cells and supramolecular materials field due to their unique physicochemical characteristics and self-assembly properties.The research of such molecule on structure design,synthesis and performance has become a hot topic,and a variety of polycyclic aromatic hydrocarbon derivatives displaying unique self-assembly structure have been prepared by precise design.In addition,compared with full carbon ones,modificating molecular skeleton by introducing heteroatoms such as fluorine,nitrogen,sulfur and oxygen usually lead to dramatic changes in their physicochemical and/or electronic properties.In addition,polycyclic aromatic hydrocarbon derivatives with high structural symmetry often exhibit unique physical and chemical properties.And the introduction of flexible side chains on the periphery of their rigid skeletons can not only improve the solubility of polycyclic aromatic hydrocarbons,but also the interactions between the side chains,and the microphase separation between the flexible side chains and the rigid skeletons can also promote the formation of a regular supermolecular structure of polycyclic aromatic hydrocarbon derivatives and exhibit excellent self-assembly performance.Therefore,in order to explore the effects of different symmetry structures and flexible side chains on molecular synthesis,self-assembly morphology and properties,in this dissertation,a series of novel sulfur-fused polycyclic aromatic hydrocarbons(S-PAHs)with highly symmetrical structures(D6h-hexagonal,C3-triangle and C2-rectangle shape)were designed and synthesized.Their structures were characterized by fourier transform infrared spectra(FT-IR),NMR spectroscopy and MALDI-TOF mass spectrometry.By connecting different side chains,using TGA/DSC test their thermal properties,UV-vis and fluorescence spectra test their spectral characteristics,CV test their electrochemical performance,and SEM/TEM,STM test their self-assembly properties in the solution and on the surface.The major contents of this dissertation are as follows:1.The synthesis of novel D6h-hexagonal-shaped sulfur-fused polycyclic aromatic hydrocarbons.We designed seven kinds of D6h-hexagonal-shaped sulfur-fused polycyclic aromatic hydrocarbons and they were successfully synthesized from 3-bromoiodobenzene as starting material by several steps.The S-PAH(1)with six hydrophilic triethylene glycol chains was synthesized by Scholl-type oxidative cyclization of the corresponding precursor 24 using FeCl3(48 eqv)as a mild oxidant in CH2Cl2/MeNO2 for 2 hours.The similar synthesis method was used to synthesize the other D6h-hexagonal-shaped S-PAHs(2-7)with various substituents(six hydrophobic dodecyl chains,six hydrophilic triethylene glycol chains,various alkoxyl side chains,and various amide C=O side chains).2.The synthesis of novel C2-rectangle-shaped sulfur-fused polycyclic aromatic hydrocarbons.We designed two kinds of C2-rectangle-shaped sulfur-fused polycyclic aromatic hydrocarbons and they were successfully synthesized from 3,5-dibromobenzylbromide as starting material by several steps.The S-PAH(8)with eight hydrophobic dodecyl chains was synthesized by Scholl-type oxidative cyclization of the corresponding precursor 87 using FeCl3(40 eqv)in CH2Cl2/MeNO2 for 1.5 hours.Considering that the amphiphilic polycyclic aromatic hydrocarbons could form more diverse structures,such as vesicles,spherical structures,micelles,and capsules,therefore,four hydrophilic triethylene glycol chains were introduced to the both rectangle sides,and the amphiphilic S-PAH(9)with four hydrophilic triethylene glycol chains was obtained by the similar synthesis method.3.The synthesis of novel C3-triangle-shaped sulfur-fused polycyclic aromatic hydrocarbons.2-bromoacetophenone was used as starting material,followed by Aldolization trimerization reaction,and Suzuki coupling reaction to synthesize the precursor 97 with three hydrophobic dodecyl chains.The S-PAH(10)with three hydrophobic dodecyl chains was synthesized by Scholl-type oxidative cyclization of the corresponding precursor 97 using FeC1b(36 eqv)in CH2Cl2/MeNO2 for 2 hours.The S-PAH(10)with hydrophobic dodecyl chains was characterized by MALDI-TOF mass spectrometry.4.Spectroscopic and electrochemical properties of the sulfur-fused polycyclic aromatic hydrocarbons with highly symmetrical structures(D6h-hexagonal,C3-triangle and C2-rectangle shape)were investigated.The spectroscopic and electrochemical properties of the sulfur-fused polycyclic aromatic hydrocarbons were characterized by UV-vis,fluorescence spectra,and CV measurements.UV-vis and fluorescence spectra showed broad peaks,and these results suggested that the sulfur-fused polycyclic aromatic hydrocarbons existed in certain dynamic aggregates in those solutions via intermolecular ?-? interactions,and the D6h-hexagonal,C3-triangle and C2-rectangle shaped sulfur-fused polycyclic aromatic hydrocarbons showed brick-red,red and yellow fluorescence in the solutions in turn.In addition,the cyclic voltammetry illustrated that the sulfur-fused polycyclic aromatic hydrocarbons were stronger donors and might serve as efficient active layers in photovoltaic devices.Furthermore,Chemical oxidation of the D6h-hexagonal-shaped S-PAH(1')with six hydrophobic dodecyl chains in CH2Cl2 with[(BrC6Ha)3NSbCl6]afforded two new transition peaks at 618 nm and 728 nm,along with a broad transition peak at 1000 to 1600 nm in the near-infrared region.At the same time,the ?-?*transition band(434 nm)of the neutral state gradually disappeared.Moreover,both C2-rectangle-shaped S-PAH(8)with eight hydrophobic dodecyl chains and C3-triangle-shaped S-PAH(10)with three hydrophobic dodecyl chains displayed similar changes to S-PAH(1'),therefore,the three sulfur-fused polycyclic aromatic hydrocarbons can all be oxidized by[(BrC6H4)3NSbCl6],a one-electron oxidant,to give a stable radical cation at ambient conditions.5.Self-assembly behaviors of the sulfur-fused polycyclic aromatic hydrocarbons with highly symmetrical structures(D6h-hexagonal,C3-triangle and C2-rectangle shape)were investigated.The self-assembly behaviors of the sulfur-fused polycyclic aromatic hydrocarbons with different symmetries were investigated by scanning electron microscope(SEM)and transmission electron microscopy(TEM)in different solvents.The SEM and TEM results showed that the D6h-hexagonal-shaped S-PAHs(2,4 and 5)could all self-assemble into spheres with various sizes in tetrahydrofuran.Moreover,the self-assembly behaviors showed that the C2-rectangle-shaped S-PAH(8)could self-assemble into nanofibers in both toluene and tetrahydrofuran,and the amphiphilic S-PAH(9)could self-assemble into spheres with various sizes in tetrahydrofuran.In addition,the C3-triangle-shaped S-PAH(10)with three hydrophobic dodecyl chains could also self-assemble into spheres.More importantly,the self-assembly behaviors of the sulfur-fused polycyclic aromatic hydrocarbons with different symmetries were investigated by scanning tunneling microscope(STM)at liquid-solid interfaces.The STM results indicated that the D6h-hexagonal-shaped S-PAHs(1',1" and 6)and C3-triangle-shaped S-PAH(10)self-assembled to form porous two-dimensional(2D)networks with different pore sizes at the octylbenzene-graphite interface,which was not observed in the case of C2-rectangle-shaped S-PAH(8)with hydrophobic dodecyl chains.However,at the 1,2,4-trichlorobenzene-graphite interface,the self-assembly of S-PAH(8)resulted in either porous or non-porous supramolecular 2D morphologies in different regions.Interestingly,the non-porous 2D structure was caused by the dense alignment of S-PAH(8),which was induced by van der Waals force and S…S(3.25 A)interactions.Therefore,the results constitute an important step toward the synthesis of 2D networks with controlled morphologies induced by structural symmetry.