Preparation, Research And Application Of Pure Organic Room Temperature Phosphorescent Materials Based On Amino Acid

Pure organic photoluminescence materials have received increasing attention in academia and industry due to their unique photophysical properties and a wide range of applications in chemical sensors,cell bioimaging,drug delivery and control release,and organic light-emitting diodes(OLED).So far,traditional pure organic photoluminescence materials generally contain a great many of conjugated π-aromatic units or use rare earth metals as emission units.These proportions not only affect their biocompatibility and chemical properties,but also are influenced by the “aggregation caused quenching”(ACQ)effect,which strongly limits the practical application of photoluminescence materials.Different from common fluorescence,Phosphorescence has great potential due to its continuous light-emitting property,which has attracted extensive attention from researchers.As such materials,phosphorescence usually occurs in rigid substrates at 77 K,but less at room temperature.This phenomenon is mainly due to the instability of triplet excitons,which are quenched by oxygen,humidity,and thermal motion.Therefore,designing long-lived room temperature phosphorescence(RTP)materials is challenging.In recent years,many strategies have been developed to promote the effective emission of organic phosphorescence,which includes the following two key points:(1)Improvement of the intersystem crossing(ISC)efficiency from the lowest excited singlet state(S1)to the excited triplet(Tn)or from the lowest excited triplet(T1)to the ground state(S0),which can be achieved effectively by enhancing the spin-orbit coupling or by reducing the energy gap between the singlet and triplet states;(2)Inhibition of the nonradiative transition process from the lowest excited triplet state to the ground state as much as possible as the active triplet excitons are often quenched by oxygen,solvent and high temperature.This is generally achieved by introducing microscopic rigid structures and constructing strong interactions.So far,researchers have introduced precious metals,heavy atoms,aromatic carbonyl groups,and heteroatoms to facilitate ISC process and further promote efficient RTP emission.Moreover,through the crystal,the introduction of metal organic framework,big ring main body and enhance the hydrogen bonding to build micro rigid structure and strong interaction can be achieved strong RTP emission.However,although precious metals have been proved to be effective in enhancing RTP emission,their potential physiological toxicity,scarce quantity and high price have limited their wide application.Although the use of precious metals can be avoided in molecular crystallization and metal-organic framework,the harsh preparation conditions have high requirements on solvent,temperature and impurities,which not only lead to poor repeatability,but also make the stability,flexibility and processing of the material unsatisfactory.Although the introduction of heavy atoms and halogen bonds can promote the ISC process,the emission lifetime of RTP is very short,which is close to the typical flicker time of human eyes and difficult to observe.All these have greatly hindered the application of these RTP materials.Therefore,the preparation of pure organic amorphous materials with efficient RTP emission has great significance.In this study,starting with L-Histidine,pure organic amorphous compounds with ultra-long room temperature phosphorescence emissions were prepared by ionization and the introduction of conjugated rings.We have determined the structure of the compound by means of NMR,TOF-MS,FT-IR,and XPS,and explored its photophysical properties through three-dimensional excitation fluorescence mapping spectroscopy,ultraviolet visible absorption spectroscopy,and time-resolved emission spectroscopy.It exhibits characteristics of cluster induction and room temperature phosphorescence emission,with the lifetime of histidine sodium salt RTP formed by histidine ionization reaching 283.76 ms,and a short phosphorescence lifetime of 34.33 μ s after the introduction of conjugated rings.After further ionization,the room temperature phosphorescence lifetime can reach436.44 ms,indicating the degree of conjugation in the system and the promoting effect of ion bonds on molecular RTP emission.Finally,combining theoretical calculations,the molecular configuration was optimized and its HOMO and LUOM orbitals were calculated,further explored the generation of RTP phenomena.Based on the previous work,we first prepared pure organic polymers with ultra-long room temperature phosphorescence and aggregation induced emission using the prepared small molecule compound and biological monomer p-styrene sulfonate by simple free radical polymerization of in water.The structures of the polymers were determined by NMR and FI-TR,and its photophysical properties were investigated by three-dimensional excitation-fluorescence mapping,three-dimensional excitation phosphorescence mapping,UV-vis absorption,and time-resolved emission spectra.The results showed that polymer P1 exhibited cluster induced and room temperature RTP emission in both solution and solid states,with a maximum RTP lifetime of 606.5 ms.And through the calculation of photophysical parameters of different copolymers,it is found that the stronger the conjugation degree of the copolymer system is,the higher the phosphorescence life and quantum yield are,the more red shift of emission is.Unlike previous situations where the content of phosphorescent units in polymer systems is very small,even if the proportion of phosphorescent emission units in polymers is large,it will not lead to a reduction in phosphorescent emission phenomena,and it shows good application potential in ion detection,temperature sensing,information encryption,and anti-counterfeiting.