Huiran Yang

Smart responsive phosphorescent materials for data recording and security protection

Smart luminescent materials that are responsive to external stimuli have received considerable interest. Here we report ionic iridium (III) complexes simultaneously exhibiting mechanochromic, vapochromic and electrochromic phosphorescence. These complexes share the same phosphorescent iridium (III) cation with a N-H moiety in the N^N ligand and contain different anions, including hexafluorophosphate, tetrafluoroborate, iodide, bromide and chloride. The anionic counterions cause a variation in the emission colours of the complexes from yellow to green by forming hydrogen bonds with the N-H proton. The electronic effect of the N-H moiety is sensitive towards mechanical grinding, solvent vapour and electric field, resulting in mechanochromic, vapochromic and electrochromic phosphorescence. On the basis of these findings, we construct a data-recording device and demonstrate data encryption and decryption via fluorescence lifetime imaging and time-gated luminescence imaging techniques. Our results suggest that rationally designed phosphorescent complexes may be promising candidates for advanced data recording and security protection.

A Mitochondria‐Targeted Photosensitizer Showing Improved Photodynamic Therapy Effects Under Hypoxia

Organelle-targeted photosensitizers have been reported to be effective photodynamic therapy (PDT) agents. In this work, we designed and synthesized two iridium(III) complexes that specifically stain the mitochondria and lysosomes of living cells, respectively. Both complexes exhibited long-lived phosphorescence, which is sensitive to oxygen quenching. The photocytotoxicity of the complexes was evaluated under normoxic and hypoxic conditions. The results showed that HeLa cells treated with the mitochondria-targeted complex maintained a slower respiration rate, leading to a higher intracellular oxygen level under hypoxia. As a result, this complex exhibited an improved PDT effect compared to the lysosome-targeted complex, especially under hypoxia conditions, suggestive of a higher practicable potential of mitochondria-targeted PDT agents in cancer therapy.

Water-soluble phosphorescent iridium(III) complexes as multicolor probes for imaging of homocysteine and cysteine in living cells

With the emergence of phosphorescent heavy-metal complexes as a class of attractive probes for bioimaging, there is a parallel need to develop new phosphorescent probes with complete solubility in pure water for phosphorescent staining in living cells. Herein, a convenient and general design strategy for realizing phosphorescent heavy-metal complexes with complete water-solubility is provided and a series of cationic iridium(III) complexes [Ir(C^N)2(N^N)]+PF6− (C^N = 2-(2,4-difluorophenyl)pyridine (dfppy), 2-(4-(tert-butyl)phenyl)pyridine(t-buppy), 2-(thiophen-2-yl)quinoline) (thq), 4-(pyridin-2-yl)benzaldehyde (pba)) are prepared. The water-solubility of the complexes was successfully realized through the quaternization of the tertiary amino group in the N^N ligand. By changing the C^N ligands, the luminescent emission colors of these complexes can be tuned from green to red. These cationic iridium(III) complexes are membrane-permeable and can be applied as phosphorescent dyes for cell imaging in phosphate buffer solution (PBS). Complexes Ir1–Ir3 displayed specific staining of the cytoplasm and complex Ir4 containing two aldehyde groups could detect the changes of cysteine/homocysteine concentration in living cells. These results demonstrated that our design strategy offers an effective way to develop excellent phosphorescent cellular probes for real applications.

Highly selective phosphorescent nanoprobes for sensing and bioimaging of homocysteine and cysteine

Most of reported fluorescent probes for mercapto amino acids are organic dyes. They often exhibit poor water-solubility and require the use of biologically toxic organic solvents in sensing and bioimaging. In the present study, a biocompatible phosphorescent nanoprobe by using mesoporous silica nanoparticles as carriers and an iridium(III) complex as signaling units was demonstrated. The nanoprobe exhibits a naked-eye double-signal response for the detection of homocysteine (Hcy) and cysteine (Cys) in pure phosphate buffer saline (PBS), which provides the advantage in effectively avoiding the interference from background signal of biological samples and environmental effects. In addition, the response mechanism, cytotoxicity and bioimaging were studied in detail. These results demonstrated that such a design strategy of phosphorescent nanoprobes is an effective way to develop excellent phosphorescent cellular probes for live cell applications.

A water-soluble phosphorescent polymer for time-resolved assay and bioimaging of cysteine/homocysteine

A water-soluble phosphorescent bioprobe was successfully developed by introducing an iridium(iii) complex as a phosphorescent signaling unit with poly(N-isopropylacrylamide) (PNIPAM) as the stimuli-responsive backbone. The probe was used for the effective detection of cysteine (Cys)/homocysteine (Hcy) and temperature based on changes in the phosphorescence signal. The design principle was based on the fact that the aldehyde groups in the cyclometalated ligands of the iridium(iii) complex moiety can react with the β- or γ-aminothiol group to form thiazolidine or thiazinane, respectively, resulting in a phosphorescence change in the iridium(iii) complex, thereby facilitating the detection of Cys and Hcy. Moreover, a phosphorescent hydrogel based on this probe was formed upon cross-linking and was then used as a quasi-solid sensing system for detecting Cys and Hcy. Furthermore, by using a time-resolved photoluminescence technique, the probe can detect Hcy in the presence of intense background fluorescence. In addition, phase changes in temperature-responsive PNIPAM can result in a switch of microenvironment between hydrophilicity and hydrophobicity, to which the phosphorescent emission of the iridium(iii) complex is very sensitive. This bioprobe integrates water solubility, biocompatibility, and sensing capability into one system, which is advantageous for biological applications. Further investigation of the application of the bioprobe for living-cell imaging confirmed that the probe is membrane permeable and is capable of detecting Cys in living cells with notable phosphorescence enhancement. Fluorescence lifetime imaging microscopy is successfully applied for sensing and bioimaging of intracellular Cys in the presence of short-lived background fluorescence.

Development of Upconversion Luminescent Probe for Ratiometric Sensing and Bioimaging of Hydrogen Sulfide

Merocyanines adsorbed into the mesopores of mSiO2 shell of NaYF4: 20% Yb, 2% Er, 0.2% Tm nanocrystals are demonstrated as ratiometric upconversion luminescence (UCL) probe for highly selective detection of HS(-) in living cells through inhibition of energy transfer from the UCL of the nanocrystals to the absorbance of the merocyanines. The UCL probe has been used for ratiometric sensing of H2S with high sensitivity and selectivity.

Heteronuclear phosphorescent iridium(III) complexes with tunable photophysical and excited-state properties by chelating BF2 moiety for application in bioimaging

In the present study, we explored a novel design strategy of heteronuclear phosphorescent iridium(III) complexes chelated by BF2 moiety with 3-hydroxypicolinic acid as the chelate ligand and synthesized a new series of iridium(III) complexes [Ir(dfppy)2(hpa)BF2] (1b), [Ir(ppy)2(hpa)BF2] (2b) and [Ir(tpq)2(hpa)BF2] (3b) (hpa = 3-hydroxypicolinic acid, dfppy = 2-(2,4-difluorophenyl)pyridine, ppy = 2-phenylpyridine, tpq = 2-(thiophen-2-yl)quinoline) under mild conditions. The emission colors and wavelengths of iridium(III) complexes can be affected evidently by chelating BF2 moiety into iridium(III) complexes, and this effect will be changed with the difference of cyclometalating CˆN ligands. A combination of UV-vis absorption, photoluminescence, excited-state lifetime measurements and theoretical calculations has provided the significant insight into the nature of the excited state and photophysical properties of these interesting iridium(III) complexes. Moreover, the exclusive staining of cytoplasm and low cytotoxicity were demonstrated for these new iridium(III) complexes, which made them promising candidates as multi-color phosphorescent dyes for living cell imaging.

Phosphorescent ion-paired iridium(III) complex for ratiometric and time-resolved luminescence imaging of intracellular biothiols.

A novel phosphorescent probe based on ion-paired iridium(III) complex has been designed and synthesized by incorporating α,β-unsaturated ketone moiety in the cationic component. The phosphorescent intensity of cationic component is sensitive to bithiols, such as cysteine and homocysteine, based on the addition reaction of bithiols with α,β-unsaturated ketone moiety, while that of the anionic component remains unchanged. Thus, this ion-paired iridium(III) complex can be used for ratiometric luminescence sensing and imaging of intracellular biothiols with excellent sensing performance. Moreover, the long phosphorescence lifetime of the cationic component is also sensitive to bithiols. Hence, this ion-paired iridium(III) complex has been further used for time-resolved luminescence imaging of intracellular biothiols. As far as we know, this is the first report about molecular probe for both ratiometric and time-resolved luminescence imaging of intracellular biothiols.

Dye-conjugated upconversion nanoparticles for ratiometric imaging of intracellular pH values

A ratiometric pH probe based on Tm3+ doped UCNPs functionalized with dye xylenol orange on the surface was developed, which can realize ratiometric pH sensing and imaging under continuous-wave excitation at 980 nm through the quenching and recovery of upconversion luminescence at 450 nm from UCNPs.

Luminescence Color Tuning by Regulating Electrostatic Interaction in Light-Emitting Devices and Two-Photon Excited Information Decryption

It is well-known that the variation of noncovalent interactions of luminophores, such as π-π interaction, metal-to-metal interaction, and hydrogen-bonding interaction, can regulate their emission colors. Electrostatic interaction is also an important noncovalent interaction. However, very few examples of luminescence color tuning induced by electrostatic interaction were reported. Herein, a series of Zn(II)-bis(terpyridine) complexes (Zn-AcO, Zn-BF4, Zn-ClO4, and Zn-PF6) containing different anionic counterions were reported, which exhibit counterion-dependent emission colors from green-yellow to orange-red (549 to 622 nm) in CH2Cl2 solution. More importantly, it was found that the excited states of these Zn(II) complexes can be regulated by changing the electrostatic interaction between Zn2+ and counterions. On the basis of this controllable excited state, white light emission has been achieved by a single molecule, and a white light-emitting device has been fabricated. Moreover, a novel type of data decryption system with Zn-PF6 as the optical recording medium has been developed by the two-photon excitation technique. Our results suggest that rationally controlled excited states of these Zn(II) complexes by regulating electrostatic interaction have promising applications in various optoelectronic fields, such as light-emitting devices, information recording, security protection, and so on.