Luminescent Property And Room Temperature Phosphorescence Of Nonconventional Luminogens Containing Cyano,Carbonyl And Hydroxyl Groups

Organic light-emitting materials with persistent room temperature phosphorescence(p-RTP)property have aroused extensive interest because of their unique photophysical properties and promising applications in organic light-emitting diodes(OLEDs),bio-imaging,anti-counterfeiting,etc.In recent years,it has been found that different kinds of nonconventional luminescent materials only containing nonconventional chromophores(such as aliphatic tertiary amine,carbonyl,and amide)have attracted increasing attention,due to their significant fundamental importance and promising applications.So far,the research on nonconventional luminogens is still in its infancy,and the luminescence mechanism is still under debate,with various hypotheses emerging due to the diversity of chromophores in nonconventional luminogens.To further investigate the mechanism and explore new nonconventional luminescence systems,it is essential to summarize the common rules of different systems.Therefore,this thesis explores linear polymers and small organic molecular compounds containing different atypical chromophores(cyano,hydroxyl,amide,carbonyl,etc.),and intensively investigate their different solvents and concentration solutions and different states of solids at different temperatures.The room-temperature phosphorescence(RTP)properties of these compounds,especially the emission mechanism,have been studied intensively,and the application of such compounds in the fields of anti-counterfeiting and bio-imaging were conducted.Therefore,the photophysical properties of nonconventional luminogens including linear polymers and small molecules were explored,containing varied nonconventional chromophores(such as cyano,carbonyl and hydroxyl groups,etc.).The photophysical properties and luminescent mechanism of solutions at different concentrations and solids of different states at different temperatures were further studied and discussed,especially the p-RTP property.Furthermore,those nonconventional luminogens are applied in many fields such as anti-counterfeiting and bioimaging.The major contents are summarized as follows:1).It has been found that the dilute solution of PAN is non-emissive,while the concentrated solution,solid powder and cast film can emit bright blue light under UV light,exhibiting obvious aggregation-induced emission(AIE)property,and the quantum efficiency(?)of powder can be as high as 16.9%.Through the investigation of the low-temperature luminescence properties of gradient PAN solution and different content of PAN/PMMA cast films,the emission mechanism of PAN was deeply explored.It was found that the formation of cyano clusters was the key factor,and the clustering-triggered emission(CTE)theory was clearly proposed.More interestingly,PAN powder enjoy RTP emission.The simple structure,relatively good thermal stability,chemical inertness to external environment(i.e.solvent,p H),and moreover intriguing photophysical behaviors,especially its RTP of PAN render it highly promising as a model system for the investigation of unorthodox luminogens.2).Three kinds of carbonyl-containing amorphous linear polymer polyacrylic acid(PAA),polyacrylamide(PAM)and poly(N-isopropylacrylamide)(PNIPAM)were synthesized by free radical polymerization.The results show that these polymers were nonluminescent in dilute solutions,while being highly emissive in concentrated solutions,nanosuspensions and solid powders/films,and concentrated solution at 77 K has excitation-dependent multicolor phosphorescence which can well be rationalized by the CTE mechanism,as supported by further thermoresponsive emission,cryogenic and AIE experiments,alongside with single crystal analysis.The cast films were higher ? than powder,and the PAM film has the highest ?(13.7%)and lifetime(<?> 117.0 ms).Further studies have found that the p-RTP properties of these polymers can be adjusted under different conditions.After ionizing the PAA powder with Na OH,the ? increased by 40.8%and the lifetime increased by 69.9% of PAANa.After the PAM powder was ionized with HCl,the ? increased by 50.3% and the lifetime increased by 16.5% of PAMHCl.PNIPAM does not have RTP property in air.It exhibits p-RTP property under a nitrogen atmosphere or vacuum,and the ?/<?> reached 9.6%/89.4 ms,and the <?> of powder after been pressured increases by 37.8%.The monomer of the polymer also emits light.There are a large number of intermolecular interactions such as C =O···N in the single crystal structure of acrylamide and N-isopropylacrylamide,forming a three-dimensional(3D)space electron interaction channel.It is further proved that the CTE mechanism can reasonably explain their luminous behavior,that is,the clustering of atypical chromophores such as amino and carboxyl groups in the compound,which expands electron delocalization,increases the conjugation of the compound and he degree of conformational rigidity,which make it easily stimulated emission.It also shows the potential application prospects of anti-counterfeiting,encryption and bio-imaging of these solid with p-RTP emission capabilities.3).It was found that both citric acid(CA)and trimethyl citrate(MTCA)have fluorescence and p-RTP luminescence properties,the <?>reached 416.0 ms(CA)and 845.0 ms(MTCA),while the synthetic n-butyramide citrate(N-BTCA)had no RTP emission,demonstrating that the p-RTP emission of atypical luminescent small molecules can be modulated by molecular design.The results show that the concentrated solutions of these three compounds have excitation wavelength-dependent emission and low temperature polychromatic phosphorescence.The CA and MTCA crystals exhibit a unique multi-color persistent p-RTP from blue-to-green.In the CA and MTCA single crystals,the molecules expand through the C-O···O=C interaction to delocalize the electrons to form a 3D electronic communication network.At the same time,the conformational rigidity of the conjugate-promoting cluster is increased,which is beneficial p-RTP emission.According to the CTE mechanism,the lifetime at different excitation,single crystal analysis and theoretical calculations prove that the key to the multicolor phosphorescence emission is the multi-emission center formed by the difference in structure and size of the cluster.It is found that the CTE mechanism can not only explain the intrinsic luminescence of these nonconventional luminogens containing n and ?electrons,and can also reasonably explain the phenomenon of multi-color emission.4).The luminescent properties of polyhydroxyl groups containing lone pair electrons and single bonds were investigated including glycerol(Gl),pentaerythritol(PER),D-(+)-xylose(D-Xyl),D-fructose(D-Fru)and D-galactose(D-Gal),the results indicate that the covalent bond type is not the main factors affecting the multi-color emission.The results show that these compounds have AIE properties,low temperature concentrated solutions and crystals have excitation wavelength dependent persistent multicolor phosphorescence phenomenon,the lifetime of PER crystals reached 1446.3 ms at room temperature,which is one of the longest-lived atypical luminescent compound previously reported.Under the same conditions,the color changing ability of these single crystals are as follows: D-Xyl>D-Gal>D-Fru>PER.There are abundant O···O interactions in these single crystals,and various oxygen cluster structures are formed through the 3D electronic communication network,forming multiple emission centers.Although the structures of the three monosaccharide molecules are similar,they exhibit different photophysical properties under the same conditions,especially the multicolor p-RTP emission ability,wherein the D-Xyl crystal has the widest range of discoloration.The further emission mechanism can find clues from the detailed single crystal analysis and simulation of their monomers and dimers.In a word,the multicolor emission caused by the delocalized conjugate expansion of n electron and molecular packing types.5).The luminescent properties of three cyclodextrins(CDs)containing polyhydroxy groups in a single molecule were investigated.It has been found that both the concentrated solutions(77 K)and crystals of?-CD,?-CD and ?-CD have excitation wavelength-dependent multicolor p-RTP properties,the change color ability of single crystal is?-CD>?-CD>?-CD,which proves that the number of units in the ring can be precisely changed to adjust the polychromatic p-RTP properties of the single crystal.The three types of CD single crystals contain a variety of cluster structures formed by rich O···O interactions,which gives them p-RTP emission capabilities.Among them,?-CD has the longest room temperature lifetime 286.3 ms.In order to further investigate this unique differential color-changing ability,detailed single crystal structure analysis and theoretical calculation were carried out.?-CD has the most types and intra molecular and intermolecule interactions results in more multiple emission centers.Applied studies have shown that CD molecules can use in cell fluorescent microscopy.The polychromatic luminescence of CD molecules has been successfully applied to covalent organic frameworks(COFs),and has multiple security functions.This result is of great value for intracellular microscopic imaging research.Through the above results,it can be proved that the polychromatic p-RTP emission properties of the crystal can be controlled by changing the number of CD molecule sugar units,and the regulation mechanism is reasonably explained,which has certain guidance for the preparation of adjustable multicolor luminescent materials.