Synthesis And Photoproperties Of D-?-A Type Hexaarylbenzenes

Hexaarylbenzene derivatives(HABs)have attracted a lot of research interest because of their significant role as organic light-emitting diodes,liquid crystal materials,redox materials,sensors,biomedical imaging.In “push-pull” molecular systems,intramolecular charge transfer(ICT)takes place between the donor(D)and acceptor(A)moieties upon photoexcitation,and their electronic and photophysical properties are normally associated with the ICT transition.Therefore,HAB luminescent materials with unique photophysical properties probably can be produced by decorating HAB framework with D and A groups.Herein,five five D-?-A-type hexaarylbenzene derivatives bearing methoxy and dicyanovinyl groups as electron-donating and-accepting units respectively,have been designed and synthesized and their photophysical properties have been investigated.The target HPB fluorophores 1-5 were synthesized by the Knoevenagel condensation of malononitrile with corresponding HPB aldehydes,which were previously obtained via the Diels-Alder reaction of tetraphenylcyclopentadienone derivatives and alkyne aldehydes.As for tetraphenylcyclopentadienone intermediates,they were synthesized by Knoevenagel condensation reaction from 1,3-diarylacetones and 1,2-diaryl ethylenediones(or phenanthrene-9,10-dione).All of the compounds were characterized by IR,NMR and high resolution mass spectrum(HRMS).The luminescent properties of fluorophores 1-5 were subsequently investigated through UV-vis and fluorescence spectroscopy.In these compounds,a charge transfer occurred from the electron-donor to the electron-acceptor group upon photoexcitation and ICT excited states were generated.With the increasing of the solvent polarity,bathochromic-shifts of emission spectra were observed,while the intensity gradually increases to a maximum and then decreases by degrees.In addition,compounds were 1-5 were found to exhibit large Stokes shifts,freezing-solution induced chromism and aggregation-induced emission enhancement.The thermal properties of fluorophores 1-5 were investigated by thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC).It was found that fluorophores 1?2?3?5 exhibited good thermal stability,while that of 4 containing triphenyl unit was poor.