Design,Synthesis And Properties Of Bay-functionalized Perylene Bisimide Discotic Liquid Crystals

In the past decades,perylene bisimides(PBIs)have been not only considered as important semiconductor materials with high electron affinity and strong fluorescence,but also recognized as excellent building platforms to construct well-defined supramolecular structures based on their unique ?-? stacking.Meanwhile,PBIs have evolved as one of the most intensively investigated classes of discotic liquid crystal(LC)molecules,which could self-assemble into columnar mesophases with one-dimensional charge carrier migration for potential application in electronic and optoelectronic devices such as photovoltaic cells(OPVs),organic field effect transistors(OFETs)and organic light-emitting diodes(OLEDs).The development status of PBI-based liquid crystals was comprehensively reviewed and analyzed in this thesis,it was found that the spatial hindrance of the substituents at the bay-positions would weaken the ?-? interactions of perylene core during the self-assembly process,impeding the perylene cores from piling up.The substituents of bay-positions could turn the values of perylene core absorption and emission peaks,but the serious ACQ fluorescence quenching of PBI-based liquid crystals occurred in the solid and liquid crystal states.Herein,this thesis chose 1,7-dibromoperylene tetracarboxylic acid bisanhydride and 1,6,7,12-tetrachloroperylene tetracarboxylic acid bisanhydride as the building blocks,a series of bay-functionalized PBI-LCs were designed and synthesized in high yields.Their structures were fully confirmed by means of NMR,MS,FR-IR and elemental analysis techniques.The LC behavior was studied by DSC,POM and XRD.The photophysical properties were systematically researched via UV-vis absorption and fluorescence emission spectra.In addition,the relationship between the structural and functional features of the target compounds were discussed in detail.The research of this thesis may provide some good strategies for the design and synthesis of novel PBI-LC with excellent columnar mesomorphic property and strong fluorescence in both solution and solid state.In this thesis,the work may be summarized as the following aspects:(1)Series of triads and pentads of PBI-cholesterol derivatives with two cholesterol units at the bay-position or four cholesterol units at the bay-position and N-imide position were designed and synthesized in yields of 55–65%.The influence of the different number and position of cholesterol substituents on mesomorphic and photophysical properties was studied.(2)The 1,7-bay-modified PBI-LC with two AIE-active diphenylacrylonitrile groups was creatively obtained.This PBI not only exhibited stable columnar liquid crystalline behaviour but also showed strong fluorescence with large pseudo Stokes shift in polar solution.The FRET phenomenon and AIE effect were observed for PBI-LC for the first time.(3)The PBI-LCs bearing six peripheral alkyl substituents on both 1,6,7,12-bay positions and N-imides positions were designed and synthesized in yields of 72–77%.They not only showed good liquid crystalline properties,but also enhanced the luminescent properties greatly.The PBI-LCs with good fluorescence emission both in solution and solid film were observed.(4)Series of PBI-LCs including 1,6,7,12-tetrachloro-PBIs with 2,4 and 6 peripheral alkyl chains at the N-imide positions and 1,6,7,12-tetra-p-nonylphenol bay-substituted PBIs with 6,8 and 10 peripheral alkyl chains at both the N-imide and bay-positions were synthesized and characterized.Four p-nonylphenol units at the bay-positions enhanced fluorescence with large Stokes shift and decreased the phase transition temperature.The increase in alkyl chains resulted in higher fluorescence and lower phase transition temperature.(5)The AIE-perylene LC was designed and synthesized by bridging the AIE-active diphenylacrylonitrile group and perylene core with a soft alkyl chain.The mesomorphic studies suggested that it showed a stable hexagonal columnar mesophase.Moreover,in aggregated or solid state,this perylene derivative exhibited strong fluorescence with a large pseudo Stokes shift based on the cooperative mechanism of AIE and FRET effects.