Photophysical Properties Tuning Strategies Of Phosphorescent Transition-Metal Complexes And Their Application Study

Phosphorescent metal complexes have been attracting wide spread interest in recent year because of the excellent photophysical properties, such as high luminescence efficiencies, significant Stokes shifts and easy-to-ajust emission properties. And all these merits make phosphorescent metal complexes been promising for various applications such as organic light emitting diodes (OLEDs), light-emitting electrochemical cells (LECs), phosphorescent sensor and bio-imaging. However, the traditional photophysical properties tuning methods are mainly based on the chemical modification of the existing ligand or construction of new ligand skeleton, which always involves the complicated chemical reaction. With the ongoing development of materials science, however, this tradition construction strategy of new metal complexes have seriously limit the further developments of metal complexes. Therefore, it is necessary to develop new construction methods and photophysical tuning strategies of metal complexes, which will offer an opportunity to further expand the application space of phosphorescent metal complexes in optoelectronics device field. In this thesis, we have carry out the research as follows.1. The new photophysical properties tuning strategy of ionic iridium complexes based on conterions2-(2-pyridyl)benzimidazole was chosen as N^N ligand to synthesise the cationic iridium complexes [(ppy)2IrNH]+A-.Through single crystal diffraction and’H NMR we have demonstrate that there exist hydrogen bonding interaction between conterions and cation centre in both solid and solution state, except for electrostatic interaction. The conterions depended photophysical properties of [(ppy)2IrNH]+A-were investigated through photoluminescence spectrum. In CH2Cl2solution, as the changes of conterions, the emission wavelength of complex [(ppy)2IrNH]+A-can be regulated continuously between490nm and584nm. By contrast with1H NMR spectra of iridium complexes with various conterions, in combination with calculated results, we conclude that the couterions depended photophysical properties is the result of electronic structure changing of hydrogen donor, which is affected by the counterions.2. The piezochromic and electrochromism of ionic iridium complex with hydrogen bond donor in the ligand, mechanism and application study.We have prepared and discovered cationic complexes [(ppy)2IrNH]+A-exhibiting a fascinating piezochromic and electrochromism phosphorescence. For piezochromic, the emission colour of complex in solid can be switched revcrsibly by grinding and vapour fuming. Based on the PXRD, CP/MAS, NMR and IR studies, we found that this piezochromic phosphorescence origin could be attributed to a hydrogen bond destruction and restoration along with amorphous-crystalline phase transformation. For electrochromism, the emission colour of complex in acetonitrile solution can be switched reversibly by adding and removing electric field. Based on the1H and19F NMR and CP/MAS, we found that this electrochromism phosphorescence origin could be attributed to the polarisation of the N-H bond of the ligand under external electric field. Finally, we have designed optical and electric recording devices based on the piezochromic and electrochromism, respectively.3. Study on the spectra response mechanism of three ionic iridium complexes with different cyclomedtalating ligand to fluoride ion, by1H NMR and theoretical calculation.We have synthesised three ionic iridium complexes with different cyclomedtalating ligand based on2-(2-pyridyl)benzimidazole as N^N ligand:[(2fnpy)2IrNH]+PF6-,[(ppy)2IrNH]+PF6-and [(tpq)2IrNH]+PF6-. The response of iridium complexes to fluoride ion were studied through the UV-vis absorption and photoluminescence spectra. As the addition of fluoride ion, the emission properties of this three iridium complexes show different changes. For [(2fnpy)2IrNH]+PF6-the emission will be quenched, and for [(ppy)2IrNH]+PF6-the emission will be blue-shift, whereas [(tpq)2IrNH]+PF6-will be red-shift. The]1H NMR changes of iridium complexes with the addition of fluoride ion shown that at the low concentration of fluoride ion it formed firstly hydrogen bond between fluoride ion and NH group, with the increase of fluoride ion concentration the NH group will be further deprotonated, in consequence, the ionic iridium complexes will be changed to neutral iridium complexes.4. Heteronuclear phosphorescent iridium(Ⅲ) complexes with tunable photophysical and excited-state properties by chelating BF2moiety for application in bioimagingIn the present study, we explored a novel design strategy of heteronuclear phosphorescent iridium(Ⅲ) complexes chelated by BF2moiety with3-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 BF2moiety into iridium(Ⅲ) complexes, and this effect will be changed with the difference of cyclometalating CAN 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 make them promising candidates as multi-color phosphorescent dyes for living cell imaging.5. Design of nano materials with aggregation-induced phosphorescent emission and their promising applications in time-resolved luminescence assay and targeted phosphorescence imaging of cancer cellsA series of cyclometalated Pt(Ⅱ) complexes with AIPE properties have been exploited, we demonstrated their application in time-resolved luminescence assay to eliminate the interference from background fluorescence utilizing the long emission lifetime of phosphorescent signal, which is their advantage compared with fluorescent organic dyes. Moreover, the targeted phosphorescence imaging of cancer cells based on AIPE-active polymer nanoparticles have been realized.