Synthesis And Properties Of Stimulus-Responsive Organic Circularly Polarized Fluorescent Materials

Chirality of a molecule means that a molecule is non-overlapable with its mirror image,a form of stereoisomerism commonly referred to as enantiomerism in chemistry.Chirality plays a crucial role at the molecular scale and even in the evolution of life on Earth.Meanwhile,scientists are gradually applying chirality to more aspects,such as the synthesis of chiral drugs,asymmetric synthesis,circularly polarized luminescent material,chiral devices,and information encryption.Here,Circularly polarized luminescence refers to the phenomenon that chiral luminescent materials emit different left-or right-handed circularly polarized light under the irradiation of excitation light of a fixed wavelength.Organic Circularly Polarized Luminescence(CPL)materials are one of the materials that have unlimited potential for future development and have potential applications in the fields of three-dimensional optical display,information encryption,chiral electronics,etc.,and have attracted a lot of attention from researchers.Among organic CPL materials,organic small molecule circularly polarized luminescent materials are also more suitable than other materials in biological probe and bioimaging due to their unique properties such as small relative molecular weight,easy accessibility,good solubility.Generally,organic CPL materials can be obtained through 1)linking the luminescent components to chiral organic small molecules or polymers by covalent bonds;2)linking the chiral side chains to the conjugated luminescent polymers by covalent bonds;3)combining the chiral molecules and luminescent molecules by noncovalent bonds interactions,like hydrogen bonds,electrostatic interaction,?-?stacking,ligand coordination,etc.,which is known as supermolecular assembly.Organic CPL materials prepared through supermolecular assembly have raised a lot of interests because of their solution processability and easy functionalization.In general,a supermolecular assembly with CPL property has two parts: one provides chirality and the other provides luminescence.There are three typical approaches to generate CPL for supramolecular assemblies:1)The achiral fluorescent molecule selfassembles under certain conditions;2)The chirality can be transferred from the chiral molecule to the non-chiral fluorescent molecule through the assembly;3)The chiral fluorescent molecule assembles asymmetrically.CPL materials can be prepared by rational molecular design and using supramolecular assembly methods.In this thesis,three anthracene derivatives were designed and synthesized by linking different chiral groups with anthracene as the core,and organic circularly polarized fluorescent materials were prepared using the assembly method.It is shown that the assembly of aggregation-induced luminescence(AIE)molecule 9,10-diethylenebis(4-pyridyl)anthracene(BP4VA)with chiral molecule 1,3,5-trimethyltriglutamate hexaethyl ester(TMGE)can construct CPL supramolecular assemblies with acid-stimulated response properties;the CPL molecule 9,10-diethylenebis(benzamide-The change of chirality of CPL molecule 9,10-diethylenebis(benzamide-phenylethylamine)anthracene(R/SDSA-2PEA)can be achieved by changing the solvent polarity.1.Acid stimulus response CPL luminescent materialCPL supramolecular assemblies with acid-stimulation-responsive properties were constructed by assembling a typical aggregation-induced luminescence(AIE)molecule,9,10-diethylenebis(4-pyridyl)anthracene(BP4VA),with a self-assembled chiral molecule,1,3,5-trimethyltriacylglutamic acid hexaethyl ester(TMGE).SEM,TEM and fluorescence images proved the successful assembly of BP4 VA and TMGE.The fluorescent emission peaks of the assemblies were the same as that of BP4 VA in solution,but the intensity was significantly stronger than that of BP4 VA in solution due to the aggregation of BP4 VA in the assembly.The CD spectra of the supramolecular assemblies showed that chirality could be transferred from the chiral molecule TMGE to the achiral molecule AIE(BP4VA)by co-assembly.Under the stimulation of trifluoroacetic acid(TFA),BP4 VA containing pyridine groups was protonated and the CPL wavelength of the assemblies was red-shifted,while the morphology of the assemblies did not differ significantly before and after protonation.The study provides an effective strategy to prepare stable acid stimulus responsive CPL materials through the assembly of AIE molecules.2.CPL material with solvent effectUsing tetraethyl-9,10-diyl bis(methylene)bisphosphonate anthracene and paldehydbenzamide-phenethylamine as reactants,throught Hornal-Wadsworth-Emmons reaction(HWE reaction)synthesized 9,10-diethylenebis(benzamidephenethylamine)anthracene(R/S-DSA-2PEA)with aggregation-induced luminescence properties.The UV absorption and fluorescence spectra in different polar solvents show that S-DSA-2PEA has a solvation effect;CD spectroscopy studies show that the two molecules have chirality.Therefore,it can be expected that these two molecules can realize circularly polarized light emission,and the chirality can be changed by changing the polarity of the solvent.