Synthesis And Optical Properties Of D-A Hexabenzocoronene Compounds

Graphene has become the focus of material scientists due to its special physical and chemical properties.Because graphene is a zero band gap semiconductor,which limits its application in electronic devices,this problem can be solved by limiting the size of graphene and opening the band gap through physical and chemical methods.But this"top-down"method can not obtain accurate structure and size of materials,people began to explore the"bottom-up"chemical synthesis of molecular nanographene.Nowadays,planar nanographene,carbon nanotubes,nanowires and planar twisted nanographene with precise structure have been successfully synthesized.Hexabenzocoronene?HBC?can be seen as the simplest nano-graphene with a size of about 1 nm.Various derivatives of hexabenzo-myristate have been synthesized and widely used in the fields of organic light emitting diodes,field effect transistors,solar cells and energy storage materials.However,there are few studies on D-A hexabenzocoronene derivatives at this stage.In this paper,a simple method for the synthesis of formylhexabenzocoronene was explored.A series of hexabenzocoronene derivatives with D-A structure were further synthesized using it as the parent,and the photophysical-photochemical and thermal stability properties were studied.The main research results are as follows:1.Simple synthesis of formylhexabenzocoronene.The precursor formyl hexaphenylbenzene was first explored and synthesized,and then the target product formylhexabenzocoronene was synthesized by three methods of Scholl reaction dehydrogenation coupling cyclization.Among them,the solvent-free ball mill grinding method has the advantages of short reaction time,simple operation,easy separation and high yield?yield 92%?.The structure was optimized by theoretical calculation and the electronic distribution was calculated.The photophysical properties of the compounds were studied by UV-vis absorption spectra and fluorescence spectra.2.Hexabenzocoronene-base derivatives with D-A structure were synthesized by Knoevenagel reaction using formylhexabenzocoronene substituted by two malonitrile compounds.The molecular frontline orbits of compounds and the electronic distribution of their molecules were analyzed by theoretical calculations.The photophysical properties of the two compounds were studied and it was found that the fluorescence spectra gradually red-shifted with the increase of solvent polarity due to intramolecular electron transfer,with a maximum Stokes shift of 290 nm and a maximum absolute quantum yield of 46%.Thermogravimetric analysis showed that the two compounds had excellent thermal stability,with a weight loss of less than 5%at400?.Among them,malonitrile substituted compounds can be used as fluorescent probes for hydrazine hydrate with a detection limit of 1.6×10^-7 M.3.Two cyclic diketones substituted D-A hexabenzocoronene-base derivatives were synthesized.The conjugate system of the molecule is expanded.It is found by theoretical calculation that the HOMO and LUMO orbitals are separated obviously,the energy gap is reduced,and the lowest energy gap is 2.67 eV.It was found by fluorescence spectroscopy that the red shift of the fluorescence emission peaks of these two compounds was more obvious with the increase of solvent polarity,with a maximum Stokes shift of 371 nm and a maximum absolute quantum yield of 55%.There are 73 pictures,6 tables,and 98 references in this paper.