Photophysical Properties And Supramolecular Self-Assembly Of Multi-Sulfurated Aromatic Compounds

Luminescent materials including organic fluorescence,phosphorescence and delayed fluorescence are one of the study hotspots,since they exhibit great application value in various fields,such as biological imaging,organic light emitting diode,sensing,data storage and information security.Lately,organic fluorescent and phosphorescent dual emission molecules have just aroused some research interests due to the collection of respective advantages of fluorescence and phosphorescence.On one hand,they still lack thorough investigation and their molecular species are limited.Thus,the design and the exploration of the emission mechanism of the material show great potential.On the other hand,the polysulfide aromatic compounds have showed some unique photophysical properties,especially the room temperature phosphorescence properties which were rare in pure organic molecules.For example,these compounds give phosphorescence emission with the aggregation-induced emission,whereas the phosphorescence quantum yield of some of these compounds can reach as high as 100%.Based on the facts above,we studied the photophysical properties of a series of polysulfide aromatic compounds and regulated their emission properties by self-assembly.First,we used a single asterisk phosphorescent luminophore as a template and then modified six amide bonds onto the peripheral of hexathiobenzene core.The compound showed the phosphorescence-fluorescence dual emission and multi-color luminescence properties which were induced by hydrogen bond induced self-assembly.The molecule also responded to various scales of solvent conditions or mechanical stimuli.Then,we added the chiral?-lipoiate side groups on the peripheral of the hexathiobenzene core.The chiral molecule first showed phosphorescence emission in the monomeric state and then fluorescence emission in the chiral self-assembly.Given that,switching between fluorescence and phosphorescence was achieved,in which the chiral self-assembly played an important role.Next,to overcome the limit of hexathiobenzene molecules in visible light emission,we replaced the benzene ring with a naphthalene ring with greater degree of conjugation,which expanded the emission range of molecule to the near infrared region,and regulated the self-assembly and emission properties by CH-?role.Finally,studied the tetra-substituted multi-sulfurated aromatic compounds.Instead of using relatively simple self-assembly-driven force as in the previous chapters,employed various non-bond forces such as the fluoride hydrogen bond,CH-?,?-?and S-S to regulate the conformation and luminescence properties of compounds,therefore acquired the compounds that showed more complex emission properties.Our work can be summarized as follows.1 Obtained a phosphorescence and fluorescence dual emission multi-amides hexathiobenzene compound 2-1,to regulate the emission properties of the asterisk molecule by self-assembly through intermolecular hydrogen bonding.The compound exhibits two features:1)a multi-color luminescence among green,blue,white and yellow can be observed in solution as well as in solid state,by tuning the phosphorescence/fluorescence proportion with respect to the alternation of molecule stacking.Such multi-color luminescence is caused by the different vibrational excited states of the molecule;2)the compound shows sensitive response performance when it was stimulated by solvent and mechanical stimuli and causes the change in self-assembly and emission color.The molecule also has a self-recovery property in emission color after mechanical stimuli,which is a result of its self-growth induced by the relatively strong hydrogen bonds.2 Designed a hexathiobenzene based single-luminophore 3-1 with chiral R-lipoiate side groups.By ultraviolet and fluorescence spectrum study,demonstrated that the molecule shows obvious conversion from phosphorescence to fluorescence emission in DMF and water.We also delicately analyzed the chiral self-assembly behavior of compound by TEM,SEM,NMR,CD and computational simulation,and found that it emits phosphorescence in single molecule state and fluorescence in the chiral self-assembled state.From excitation and low temperature emission spectrum study,discovered that such an emission conversion is caused by different molecular vibrational excited states to control the intersystem crossing progress.Furthermore,observed reversible mechanoluminescence and chiral of the corresponding solid sample through an analogous molecular self-assembly alternation.3 Employed octathionaphthalene based on single-luminophore 4-1 as prototypes and witnessed a complex emission composed of visible fluorescence and near-infrared phosphorescence in mixed DMF/H₂O solution and in the solid state.Further analyzed the variability of the self-assembly behaviors of the compound by TEM and XRD.After the study of single crystal,found that the molecule has both planar and twisted molecular conformations.This is mainly due to the intensity adjustable CH-?interaction.Such different conformations will lead to a hybrid vibrational excited state of the molecule,then followed by intersystem crossing varies to generate a complex emission composed with visible fluorescence and near-infrared phosphorescence.Furthermore,reversible mechanochromic and mechanoluminescent conversion of the corresponding solid sample can both be observed after a corresponding self-assembly alternation.4 Prepared a simple tetrakis?arylthio?benzene molecule 5-1 with multiple intermolecular interaction target spot.From ultraviolet and fluorescence spectrum study,found that the molecule shows phosphorescence,fluorescence and delayed fluorescence emission in DMF and water and solid state.Confirmed various self-assembly behaviors of compound by TEM and XRD,which leads to the difference emission.From single crystal research,found fluorine hydrogen bonding dominated multiple intermolecular interactions can induce unsymmetrical and symmetrical conformations at the same time.Symmetrical molecules are only subjected to one kind of intermolecular force,while unsymmetrical molecules are subjected to a variety of intermolecular forces.This conformation and molecule stacking differences lead to varied vibrational excited states of the molecule and multi-mode emission properties in their aggregation forms.In addition,the phosphorescence-to-fluorescence proportion of the molecule can be adjusted by solvent and mechanical force.