Synthesis And Properties Of Full-Cove Edge Stepped Graphene Nanoribbons

In recent years,the whole society has higher requirements for flexible and portable electronic devices,which encourages scientists to develop new photoelectric functional materials.Among them,organic photoelectric functional materials have been rapidly developed and applied in many emerging fields with their unique advantages(solution processing,printed electronics,flexibility,low consumption,etc.),such as organic field effect transistors(OFET),organic light emitting diodes(OLED),and so on.However,in order to further improve the performance of these devices,it is necessary to control the structure of these molecular materials with atomic precision.As we all know,graphene is an excellent two-dimensional conductor material with zero band gap with high conductivity,which limits its application as semiconductor.However,by adjusting the bandwidth and edge structure of graphenethe band gap and semiconductor properties of graphene nanoribbons(GNRs)can be effectively regulated,so that they can be truly applied to the field of semiconductor devices.GNRs exhibit unique semiconducting electronic and optical characteristics,which strongly depend on their bandwidths and edge structures.GNRs obtained by bottom-up solution synthesis method can accurately control its edge structure,bandwidth,band gap and photoelectric function with atomic precision.However,planar GNRs synthesized still has some drawbacks,such as poor solubility caused strong molecular packing,inconvenience for subsequent functionalization and device processing,etc.Non-planar GNRs are expected to solve the above mentioned problems and provide semiconducting materials with easy processing and adjustable functions for semiconductor devices.In this thesis,two kinds of GNRs with different lengths were designed by using contorted hexabenzocoronene(c-HBC)as the basic unit.Molecules 1a and 1b are GNRs with two c-HBC units,which have cove edges and take the form of a ladder.In addition,its edge structure is composed of [4]helicenes and contains multiple concave surfaces,and the molecule exhibits a non-planar twisted configuration.By extending the GNRs in one-dimensional direction,a graphene nanoribbon(1c)with three c-HBC subunits is designed,which helps to form long-range ordered carrier transport channels and improve the carrier mobility of carbon nanoribbons.Unfortunately,molecule 1c has not been successfully isolated or synthesized at present.Different from the traditional method of synthesizing c-HBC by Barton-Kellogg reaction,the strategy of "skeleton construction-post modification" was adopted in this thesis to successfully obtain the target molecules,which provides a new way to synthesize c-HBC multimer.This method adopts a tidy synthesis strategy,which greatly improves the stability and reaction yields of intermediates,and can integrate different functionalities,which is beneficial to study the effects of different functionalities on molecular properties.Compared with planar GNRs,this type of multi-concave GNRs have dynamic multi-concave structure,good solubility and easy processability,which makes them potentially important candidates for semiconductor applications,and provides meaningful exploration and potential organic photoelectric materials to meet the future needs of semiconductor devices.