Controlled Synthesis And Self-Assembly Of Novel "Rod-Coil" Brush-like Macromolecules Containing Graphene Nanoribbons And Their Polyphenylene Precursors

Recently,a novel ribbon-like nano-graphene materials,which are graphene nanoribbons?GNRs?,have attracted great attention as candidates for next-generation semiconductor.Their particular structures,such as controlled width and edge structures,endow them with excellent photoelectric properties.Thus,GNRs are considered as the most promising semiconductor materials.Nevertheless,so far,GNRs have no side substituents or side chains,which greatly limits their solution dispersibility and thus impedes the studies of their self-assembly and physicochemical properties in solution as well as prospective applications.Therefore,it is highly desirable to attach polymer chains or large groups with long chains onto GNR backbones,which forms novel rod-coil brush-like molecules with GNR backbones as the rod segment.The dense side chains on both sides of GNR backbones can endow GNRs with good liquid-phase dispersibility and processability.The good liquid-phase dispersibility of GNRs can provide conditions for self-assembly studies and preparation of self-assemblied functional materials of GNRs,and it is hopeful to obtain some supramolecular structures with special function,which is of great significance in the development of new materials of GNRs.In this dissertation,rod-coil brush-like GNRs grafted with polymers or large groups with long chains were prepared via solution method,their dispersibility,self-assembly behaviors,liquid-phase optical properties and device performance were investigated.At the same time,the self-assembly behaviors of novel rod-coil polymer brushes with polyphenylene?PP,precursors of GNRs?as the backbone were also studied.The results obtained are summarized below:1.Controllable multi-dimentional hierarchical self-assemblies of the rod-coil polymer brushes with PP as the backbone.?1?This workpresented a novel rod-coil brush-like copolymer?PP-PEO?containing a polyphenylene backbone linked with poly?ethylene oxide??PEO?side chains.Suchbrush-likecopolymersmanifestunprecedented temperature-dependentone-dimensional?1D?and two-dimensional?2D?self-assembly in THF/H₂O solution.At 20°C,PP-PEO self-organized into nanoribbons which further twisted into ultralong helices with controlled pitch.At 10°C,quadrangular multilayer sheets of over 10?m were obtained.?2?The effect of the nature of solvents on the self-assembly of PP-PEO was also investigated.The results showed that PP-PEO presented a completely different self-assembly behavior in CHCl₃/CH₃OH.A unique ultra-large multi-layered sheet formed through hierarchicalself-assemblyofPP-PEOthroughadistinctive morphological transition of 1D helical to 2D superstructures.?3?Moreover,a carboxyl-functionalized PP?PP-COOH?was prepared and its pH-responsive hierarchical self-assembly behaviors in THF/H₂O were investigated.As found in the study,the macromolecule self-organized into 1D thick fibers at pH=8,and could form ultralong helixes at pH=10.When the pH value was about 13,PP-COOH self-organized into uniform tubes.The above studies provide a new system for the self-assemblies of rod-coil brush-like copolymer,which broadens the research scope of the self-assembly of rod-coil graft copolymer.Moreover,it will be a reference for the studies on self-assembly behavior and mechanism of rod-coil brush-like copolymer.2.A bottom-up solution synthesis of rod-coil brush-like defect-free GNRs?GNR-PEOs?grafted with flexible poly?ethylene oxide?chains?PEO?were demonstrated.Remarkably,the PEO chains renders the GNRs superb dispersibility,with a record concentration of¹ mg/mL?for GNR backbone?in tetrahydrofuran?THF?that is much higher than that?<0.01mg/mL?ofreportedGNRs.Moreover,the PEO-functionalized GNRs can be readily dispersed in water.The excellent dispersibility offers opportunities not only for deep understanding physiochemical properties of GNRs but also for developing prospective applications of GNRs.Scanning probe microscopy reveals raft-like self-assembled mono-layers of uniformGNRs on graphite substrates.Based on the above excellent dispersibility,thin-film-based field-effect transistors?FETs?of the GNRs were obtained and exhibited a high carrier mobility.This study provides a new way for improving the dispersibility of GNRs and blazes a trail for polymer functionalization of GNRs.Moreover,polymer functionalization affords chances to develop new GNR-related studies in a broad range of research areasincludingmolecularself-assembly,nanocomposites,and biotechnology.3.The functionalization of GNRs with hydrophilic side groups or chains endow GNRs with water-dispersibility and then broaden their applications especially water-based applications,such as biological applications and self-assembly studies.In this work,the successful dispersibility and self-assembly behaviors of flexible poly?ethylene oxide??PEO?chains with different lengths grafted rod-coil brush-like GNRs were demonstrated.As found that PEO coils with the largest M_n can endow GNRs with the best dispersibility in H₂O.For example,GNR-PEO2000?GNRs functionalized by the PEO with M_n of 2000?presented a concentration of 0.5 mg/mL of the GNR backbone.In addition,the GNR-PEOs presented hierarchical self-assembly behaviors and formed 1D assemblies.Here,GNR-PEO1000?GNRs functionalized by the PEO with M_n of 1000?was took as an example to study the assembly mechanism of the GNR-PEOs.As found in the results,GNR-PEO1000 firstly self-organized into 1D nanoribbons,then the nanoribbons bundled into ultralong 1D spring-like super-helices.By contrast,GNR-COOH can only be dispersed in KOH solution with a maximum concentration?GNRs backbone?of 0.5 mg/mL at pH=14,and formed large 2D raft-like assemblies.Such results make GNRs move into supramolecular fields,and makes the potential applications of GNRs extend to the field of aqueous systems,and has greatly broadened the research scope of GNRs.4.Although the functionalization of long PEO chains could greatly improve the dispersibility of GNRs,it is still far away from the realization of individual GNR dispersed in liquid-phase.Therefore,the studies on the physiochemical properties of GNRs in liquid-phase,suchas optical properties and self-assembly,are still limited to a great extent.In order to further prevent the GNRs aggregation caused by?-?stacking and obtain complete homogeneous GNRs solutions,a novel rod-coil brush-like GNR?GNR-BR-16C?functionalized by rigid endocyclio groups with long alkyl chains was designed and prepared.Remarkably,the result GNR-BR-16C can be dispersed into almost all the common organic solvents without any external assistance,the resulted solutions can reach a concentration of above 2 mg/mL and will not precipitate forever.The results of dynamic light scattering?DLS?and optical properties further conformed the excellent dispersibility of the GNRs.This is by far the GNRs with the best liquid-phase dispersibility,which is a crucial step towards the single dispersible GNRs.In addition,such excellent dispersibility create conditions for the subsequent preparation of uniform GNRs film as well as the assemblies of GNRs at liquid-liquid or liquid-gas interface,which make it possible to offer GNRs more potential applications.