Huibin Sun

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.

FRET-based probe for fluoride based on a phosphorescent iridium(III) complex containing triarylboron groups

An excellent F−probe (complex 1) based on carbazole-fluorene-carbazole (CzFCz) as a fluorescent donor and a cationic Ir(III) complex unit containing dimesitylboryl (Mes2B) groups as a phosphorescent acceptor has been designed and synthesized. Several reference compounds, such as complex 2 which is similar to complex 1 but without Mes2B groups, fluorescent donor CzFCz, and phosphorescent acceptors A1 and A2, were also synthesized in order to better understand the influence of Mes2B groups on the excited state properties and fluorescence resonance energy transfer (FRET) in this system. The introduction of Mes2B groups on the ligands of the Ir(III) complex unit can lead to a red-shifted and more intense absorption, facilitating efficient FRET from the fluorescent donor to the phosphorescent acceptor. Complex 1 displayed highly efficient orange-red phosphorescent emission with an emission peak at 584 nm in CH2Cl2 solution at room temperature. The emission wavelength of complex 1 in film is red-shifted to 600 nm with a shoulder at 650 nm, and its quantum efficiency in film was measured to be 0.15 under excitation at 450 nm. Utilizing the specific Lewis acid–base interactions between boron atom and F−, the binding of F− to complex 1 can change its excited state and suppress FRET, quenching the phosphorescent emission from the Ir(III) complex and enhancing the fluorescent emission from CzFCz. Thus, a visual change in the emission color from orange-red to blue was observed. Optical responses of complex 1 to F− revealed that it can be used as a highly selective, colorimetric and ratiometric optical probe for F− utilizing the switchable phosphorescence and fluorescence.

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.

Rational design of metallophosphors with tunable aggregation-induced phosphorescent emission and their promising applications in time-resolved luminescence assay and targeted luminescence imaging of cancer cells

A series of Pt(II) complexes with different N⁁O ligands have been synthesized and characterized by NMR, mass spectroscopy, and X-ray diffraction studies. All complexes are non-emissive in dilute solution. Interestingly, they exhibit aggregation-induced phosphorescent emission (AIPE) with an absolute quantum efficiency of up to 38% in the crystal state. In addition, their AIPE properties can be tuned significantly by changing the chemical structures of N⁁O ligands. Furthermore, an AIPE mechanism of “restricted distortion of excited-state structure (RDES)” was proposed through experimental and theoretical investigations, which provided a rational design strategy for metallophosphors with tunable aggregation-induced phosphorescent emission. Considering their excellent emissive properties in aggregation state, the promising applications of these AIPE-active Pt(II) complexes in time-resolved luminescence assay utilizing the long emission lifetime of phosphorescent signal and targeted luminescence imaging of cancer cells have been demonstrated.

An excellent BODIPY dye containing a benzo[2,1,3]thiadiazole bridge as a highly selective colorimetric and fluorescent probe for Hg2+ with naked-eye detection

An excellent red-emissive BODIPY dye containing a benzo[2,1,3]thiadiazole bridge was synthesized, and its sensing ability toward metal cations was investigated in detail. It can work as a highly selective probe for Hg2+ detected by the naked eye, with evident solution color and photoluminescence changes.

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.

CCDC 892981: Experimental Crystal Structure Determination

Related Article: Huibin Sun, Lijuan Yang, Huiran Yang, Shujuan Liu, Wenjuan Xu, Xiangmei Liu, Zhenzhen Tu, Haiquan Su, Qiang Zhao, Wei Huang|2013|RSC Advances|3|8766|doi:10.1039/c3ra40639c