Synthesis And Properties Of Fluorescent/Phosphorescent Probes Based On Organic Small Molecules And Transition Metal Iridium Complexes

Organic/transition metal complex luminescent materials luminescent materials have been widely used in the various applications in recently years,such as electroluminescence devices,photocatalytic water reduction,optical probes and cell imaging.Fluorescent and phosphorescent probes are the new materials that have attracted much more attention for its individual advantages:short response time,good selectivity,high sensitivity,low detection limits,simple and convenient operation,low cost,and important practical applications in environmental protection,medical treatment and bio-imaging.However,both fluorescent and phosphorescent probes are faced with a seriously problem:aggregation-caused quenching（ACQ）.This is not conducive for detection and thus greatly limiting the practical application of the probe,due to low luminescence efficiency in the solid or aggregatiton state.In 2001,Tang et al.found a diametrically opposite phenomenon,and named this phenomenon aggregation-induced emission（AIE）.AIE means a molecule exhibits no luminescence or weak luminescence when dispersed in good solvent and shows strong emission when aggregated or in the solid state.Since AIE solves the problem of ACQ well,optical probes with AIE characteristics have attracted considerable attention in various fileds of biology,physiology,pharmacology and environmental science.In this paper,we designed and synthesizeed several fluorescent small molecules and phosphorescent Ir（III）complexes as fluorescent/phosphorescent probes for detecting ions and explosives,and successfully achieved intracellular ultrafast and long-term bioimaging.Their photophysical properties,detection process and detection mechanism have been investigated in detail.The specific research content mainly includes the following four aspects:1.A small organic molecule with easy synthesis,high yield and very simple structure was selected and used as a fluorescent probe for sensitive and selective detection of Zn²⁺ions.In the aqueous solution,the probe molecules emit weak light,and the addition of zinc ions can significantly enhance the luminescence,while other metal ions have less influence on their luminescence.In addition,the probe molecules effectively distinguish Zn²⁺and Cd²⁺in terms of both luminescence intensity and luminescence peak position,which are difficult to be distinguished by conventional fluorescent probes.The binding ratio of the probe molecules to Zn²⁺was determined to be 2:1,and it is speculated that the mechanism may be that Zn²⁺coordinate with the hydroxyl group and the nitrogen atom from the oxazoline to form zinc complexes,which lead to the enhanced luminescence.More importantly,the probe molecules are successfully applied to the intracellular detection of Zn²⁺.This work provides a new strategy for designing ions fluorescent probes with simple structure,high sensitivity and selectivity.At the same time,their application in the biological field has been expanded in construction and can be used in practice.2.Based on the probe molecules in the first part,we used it as auxiliary ligands to synthesize four neutral iridium complexes with aggregation-induced emission enhancement（AIEE）properties by changing the different cyclometalated ligands.We studied their photophysical properties and discussed their mechanism of AIEE in detail.Based on their AIEE properties,we have found that all four metal iridium complexes can be used as phosphorescent probes to detect explosive 2,4,6-trinitrophenol（TNP）in aqueous solution with high sensitivity and selectivity.The addition of TNP results in severe quenching of the phosphorescence of the probe molecules in the aqueous solution,while those of other explosives have weak effect on their luminescence.The phosphorescent probes can also be used to prepare solid-state test strips for sensitive detection of TNP.A new detection mechanism has been discovered that has never been reported:strongly acidic TNP can react with ancillary ligands in aqueous media and decompose the complexes,causing the luminescence quenched.The mechanism was demonstrated in detail by mass spectrometry（MS）and nuclear magnetic resonance（NMR）.It has therefore been found that the ancillary ligands in this series of iridium complexes play an important role in the selective detection of TNP.This opens up a new way for the design and synthesis of phosphorescent probesto efficiently detect TNP efficiently.3.Based on the good photophysical properties of boron-dipyrromethene（BODIPY）,we designed a red emission BODIPY derivative with both twisted intramolecular charge transfer（TICT）and AIE properties.The TICT properties and AIE properties were discussed by detailed photophysical properties,and the possible mechanism for its AIE properties were investigated.This compound is then used as a fluorescent probe for the detection of fluoride anions with high sensitivity and selectivity in aqueous solution.The detection mechanism is that the nucleophilic displacement happened between the hybrid boron atom in the probe molecule and the fluoride anion,which results in the detachment of the stable difluoroboron bridge.This is confirmed by NMR and MS in detail.Intracellular imaging experiments have shown that the fluorescent probe can selectively detect fluoride anions in living cells.This work provides an effective strategy for designing and synthesizing highly efficient fluorescent probes.4.Based on the third work,we designed and synthesized three BODIPY derivatives.Through the discussion of the photophysical properties between them,it was demonstrated that the introduction of triphenylamine on the BODIPY core in molecular design is the key to endow this series of compounds with AIE properties.Three nanoparticles with good water dispersibility were prepared by encapsulating three compounds with polymer1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxyl-（polyethylene glycol）-2000](DSPE-PEG₂₀₀₀).It was found that the three nanoparticles still have very good photophysical properties,superior stability and very low cytotoxicity.They can quickly penetrate the cell membrane into the cell and produce red fluorescence,enabling ultrafast cellular imaging.Furthermore,the red fluorescent signals from these NPs can still be clearly observed after the cells have been incubated for six generations indicating that they can be used as a long-term tracer to track cancer cells.The fluorescence intensity of the nanoparticles in the tumor in U14 tumor-bearing mouse did not decrease significantly after 14 days,demonstrating that these nanoparticles also have good long-term ability to track tumor cells in vivo.The above results indicate that the compounds designed and synthesized in this work have potential application value in biology.An effective and new idea for design and synthesis fluorescent probes is provided to enrich the application of ultrafast imaging and long-term bioimaging.