Construction And Application Based On Cation-Π Luminescence System

Organic solid-state light-emitting materials are regarded as the subject of cutting-edge research in many frontier fields such as molecular luminescence and materials science,so they have caught a mushrooming number of attentions for their wide applications.However,according to the strategy currently developed,a large number of tedious synthetic steps and complicated purification procedures are usually required,and synthetic yields are usually relatively low.To make better use of their properties,the development of simple and new strategies is a general concern.Here,using commercial small organic molecules with styrene pyridine and its analogues as building units,a series of organic solid-state light-emitting materials with high yield(above 99%)and high quantum efficiency(up to 88.52%)have been synthesized.The study of the luminescence mechanism shows that this material has a unique cation-πstructure and an excimer is formed between molecules.In order to realize the application of such cation-π-induced luminophores,we have further constructed two-component and three-component composite luminescent materials.1)A two-component composite luminescent material composed of a kind of cation-πluminophore and layered nanosheets.Because the cation-π luminophore is positively charged,it can be co-assembled with negatively charged two-dimensional layered nanosheets in aqueous solution to form a new excimer to emit light.Therefore,the two-component composite luminescent material can be used to visualize the dispersion of liquid-phase exfoliated-nanosheets in aqueous solution on a large area;2)A kind of cation-7r luminophore and a phosphorescent molecule are co-doped in an amorphous polymer matrix to form three-component composite luminescent material.The three-component composite luminescent material makes full use of a commercial pure organic system without any complicated molecular design and synthesis.Since the cation-π luminophore and polymer assembly can emit orange fluorescence,it can be co-doped with blue phosphorescent organic small molecules in the polymer to adjust the color of multi-color and pure white light-emitting materials.This paper systematically studied the mechanism of solid-state light-emitting of pure organic small molecules.Two commercially available small molecules,including 4-styrene pyridine(SP)and 4-naphthalene vinyl pyridine(NP)were selected as precursors,and 4-styrene pyridinium salt(SPH)and 4-naphthalene vinyl pyridinium salt(NPH)were synthesized through a simple one-step acidification reaction.The experimental results show that there is only one cation difference in the molecular structure before and after protonation.Although they have no change in their luminescence in solution,their solid-state luminescence behavior is completely different.When the protonated molecule is in the solid state,the luminescence intensity is enhanced and the fluorescence quantum efficiency is greatly improved.Through the use of single crystal X-ray diffraction to study its intermolecular packing and intermolecular interactions,it is proved that these protonated molecules have a unique cation-π structure;in addition,through 1H-NMR,two-dimensional nuclear magnetism includes NOESY and DOSY as well as isothermal titration calorimetry(ITC)method further experimentally proved the existence of the intermolecular cation-π interactions;finally,a series of mechanism studies such as the simulation of the electrostatic potential distribution diagram and theoretical calculations showed that the excimer formed between the molecules.Therefore,due to the two synergistic effects of the cation-π interactions and the formation of excimer,the organic solid-state light-emitting molecules with high yield and high quantum efficiency formed by one-step protonation.This solves the problem of traditional organic solid-state light-emitting molecules with low yield and low luminous efficiency.The luminescence mechanism and application of a two-component composite material,which a cation-π emitter and nanosheets of layered materials co-assembled,have been studied.A new cation-π luminophore(4-formaldehyde-4-styrene pyridinium salt(FSPH))was developed,and the existence of cation-π interaction interactions between FSPH molecules was studied by single crystal X-ray diffraction.FSPH and layered materials(laponite XLG(LP)and montmorillonite(MMT))are assembled into a two-component luminescent material through electrostatic interaction.A series of characterizations such as concentration-dependent ultraviolet absorption spectroscopy(UV-vis),fluorescence spectroscopy,dynamic light scattering(DLS),potential measurement and ITC proved that the two-dimensional clay nanosheets in this two-component composite material not only greatly improved the interactions between the cation and π between FSPH chromophores,but also promoted the formation of FSPH excimer,which led to the strong luminescence of FSPH in the aqueous solution of nanosheets.With the good luminescence properties of this two-component composite material,it can be used to visualize the dispersion of LP and MMT nanosheets obtained by liquid phase exfoliation on a large scale.It is important to use fluorescence images to capture the actual dispersion state of a large number of nanosheets in an aqueous solution,which solves the problems of local characterization and difficulty in in-situ visualization in traditional transmission electron microscopy(TEM)and atomic force microscopy(AFM)characterization methods.Finally,take the cation-π luminophore(4-(4-(dimethylamino)styryl)-methylpyridinium iodide,DMP)as acceptor,phosphorescent molecule(2-hydroxycarbazole,HCB)as donor.They are doped together in amorphous polymers(polyvinyl alcohol,PVA)to form a three-component composite material,and its luminescence mechanism and application are systematically studied.Firstly,single crystal X-ray diffraction proved the existence of cation-π interactions between DMP molecules.Secondly,fourier transform infrared spectroscopy(FT-IR)and 1H-NMR spectroscopy proved that the donor phosphorescence between DMP and PVA generates room temperature phosphorescence through hydrogen bond interactions,and through’H-NMR,DOSY,NOTSY and other nuclear magnetic methods,it is proved that the acceptor fluorescent molecule DMP is doped into PVA to produce strong orange fluorescence through the cation-π interaction interactions and hydrogen bond interactions.In addition,through the energy diagram,the quantum yield and lifetime,it is proved the energy transfer process and mechanism from the triplet state to the singlet state.Finally,by controlling the process of triplet energy transfer,the broadband emission could be regulated,especially the white emission with CIE coordinates of(0.339,0.337),which solves the traditional adjustment of multi-color and white luminescent materials that are limited to occur in singlet energy transfer from the singlet state to the singlet state.