Construction And Regulatory Mechanism Of Interfacial Self-assembly For Halogenated Fluorenone Derivatives And Asymmetric Dye Molecule Controlled By Intermolecular Weak Bonding

As small organic molecules with excellent performance,fluorenone and triphenylamine-bithiophene derivatives have been widely applied in fluorescent probes,light emitting devices and solar cells.The electronic properties of the organic layer formed by these molecules can be modified by the arrangement of molecules.Therefore,it is essential to control the molecular self-assembly to tailor the electronic properties and improve the device performance.In this dissertation,we designed and synthesized a series of halogenated fluorenone derivatives to systematically explore the effects of halogen substitutes,substitute positions,concentrations,and end-groups on the self-assembly at the liquid/solid interface combined scanning tunneling microscope?STM?and theoretical calculation.We focus on the delicate interplay of weak noncovalent interactions during the self-assembly process,especially halogen bond and hydrogen bond.We successfully constructed highly sophisticated Archimedean tiling nanostructures used the“push-pull”triphenylamine-bithiophene derivative with complex molecular structure and achieved efficient capture of guest molecules,developing a supramolecular assembly model based on weak noncovalent interactions.The main works and innovative results in this dissertation are summarized as follows:?1?Self-assembled behaviors of three fluorenone derivatives substituted by different halogen atoms?X-FC15,X=Br,Cl,F?were investigated at the 1-phenyloctane/highly oriented pyrolytic graphite?HOPG?interface.By varying the solution concentrations,X-FC15?X=Br,Cl,H?can self-assemble into polymorphic nanostructures,whereas only one nanostructure can be formed by F-FC15.The results reveal that the different charge distributions on halogen substitutes lead to the subtle change of the molecular packing.The positive?-hole of Br atom is larger than that of Cl atom,while only the negative charge distributes on F atom.C-H···O=C hydrogen bonds are the main driving forces for all the assembled structures,while the halogen/hydrogen bonds act as the complementary forces to stabilize and order the self-assembled adlayers.Especially,C-H···F hydrogen bonds limit the structural polymorphism of F-FC15,while C-Br···O=C and C-Cl···O=C halogen bonds are the crucial factors for the formation of lamellar structure and dumbbell-like structure,respectively.?2?An investigation on the effects of bromine substituent positions on the self-assembly of fluorenone derivatives?X-BFC15,X=1,2,3?was performed at the 1-octanoic acid/HOPG interface.STM results reveal that X-BFC15?X=1,2,3?can self-assemble into different alternate nanostructures driven by hydrogen/halogen bonds.In addition,3-BFC15 can aggregate to form the lamellar structure at high concentration.The self-assembled characteristics are attributed to the delicate balance of the charge distribution on conjugate cores,the directionality of halogen bonds,and the close packing principle.The calculation results show that the positive?-hole of Br atom changes with the substituent positions.The increasing?-hole could strengthen the electrostatic attraction between Br and O atoms and simultaneously weaken the electrostatic attraction between Br and H atoms,affecting the competition and cooperation between halogen bonds and hydrogen bonds during the self-assembly process,and finally inducing the distinct alignments.?3?Owning to the significant role of recognition of halogen bonds in molecular self-assembly,we explored the effects of functional end-groups on the self-assembly of fluorenone derivatives?BEDF:-COOC₂H₅;BCDF:-COOH;BHDF:-OH?at the 1-phenyloctane/HOPG interface to promote the recognition of halogen bonds between the conjugated cores.BEDF,BCDF,and BHDF aggregate to form dimer structure,tetramer structure,lamellar structure and octamer structure,respectively.The results suggest that H-bonding motifs between the end-groups and the conjugated cores determine the bonding motifs of the conjugated cores,thus inducing the structural difference.-COOC₂H₅ interact with the cores as hydrogen bond acceptor to induced the dimer configuration of cores stabilized by C-H···Br hydrogen bonds,while-COOH and-OH act as both the electrophile and nucleophile bonded with the cores.Due to the difference in the secondary hydrogen bond strength and the aggregate interdigitation,type-I Br···Br bonds and halogen bonds?C-Br···O=C and Br···Br?could be formed in the self-assembly of BCDF and BHDF,respectively.The different halogen bonds could be observed at different concentrations.?4?Triphenylamine-bithiophene derivative NNDP has a complex structure with low symmetry.The self-assembly behavior of NNDP was investigated at the 1-octanoic acid/HOPG interface.STM results reveal that NNDP adopt“L”conformation and gather into chiral trimers with Baravelle spiral triangular arrangement at low concentrations.The assembly of these chiral Baravelle spiral triangular trimers results in two types of Kagoméstructures.These Kagoménanostructures are mainly stabilized by intermolecular hydrogen bonds?O-H···O?between carboxylic acid groups.Furthermore,the Kagomé-?structure displays high efficiency to capture the guest coronene molecules.These observations suggest that the complex structure of“push-pull”triphenylamine-bithiophene derivative induces the formation of sophisticated Kagométopologic structures.