Wenjuan Xu

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.

New Trends in the Optical and Electronic Applications of Polymers Containing Transition‐Metal Complexes

Polymers containing transition-metal complexes exhibit excellent optical and electronic properties, which are different from those of polymers with a pure organic skeleton and combine the advantages of both polymers and metal complexes. Hence, research about this class of polymers has attracted more and more interest in recent years. Up to now, a number of novel polymers containing transition-metal complexes have been exploited, and significant advances in their optical and electronic applications have been achieved. In this article, we summarize some new research trends in the applications of this important class of optoelectronic polymers, such as chemo/biosensors, electronic memory devices and photovoltaic devices.

Conjugated polymers with cationic iridium(III) complexes in the side-chain for flash memory devices utilizing switchable through-space charge transfer

Polycarbazole and polyfluorene containing cationic iridium(III) complexes in the side-chain have been designed and synthesized. Both polymers have been demonstrated to show conductance switching behavior and non-volatile flash memory devices based on them were successfully realized, in which the formation and dissociation of through-space charge-transfer states from the conjugated polymer “sea” to the Ir(III) complex “island”, controlled by voltage, are responsible for the conductance switching behavior and memory effect. The devices exhibit low reading, writing, and erasing voltages and a high ON/OFF current ratio. Both ON and OFF states are stable up to 107 read cycles at a read voltage of −1.0 V. Due to the different chemical structures of the polymer main-chain, the two devices show different threshold voltages. The polycarbazole derivative exhibits higher HOMO and LUMO levels compared with the polyfluorene analogue. Thus, the threshold voltage from the OFF to ON state of the device based on the polycarbazole derivative is obviously lower than that of the polyfluorene derivative-based device because of the low energy barrier between the work function of the ITO anode and the HOMO level of the polycarbazole derivative. Similarly, the threshold voltage from the ON to OFF state is evidently higher because the energy barrier of electron injection from Al into the LUMO of the polycarbazole derivative is slightly higher than that of the polyfluorene analogue. Thus, the threshold voltages of memory devices may be rationally modulated by modifying the chemical structure of polymers.

Smart Poly(N-isopropylacrylamide) Containing Iridium(III) Complexes as Water-Soluble Phosphorescent Probe for Sensing and Bioimaging of Homocysteine and Cysteine

Homocysteine (Hcy) and cysteine (Cys) are two important kinds of amino acids in human bodies. Herein, we synthesized an iridium(III) complex-functionalized poly(N-isopropylacrylamide) and its hydrogel, which could be used as the excellent phosphorescent bioprobe for sensing Hcy and Cys. Their detection can be realized in aqueous system through the variations in absorption and photoluminescence spectra. Furthermore, living cell imaging experiments demonstrate that the phosphorescent bioprobe is membrane permeable and can monitor the changes of Hcy and Cys within living cells. In addition, the probe is also thermoresponsive, and its photoluminescence intensified with increasing temperature. These results suggests that this bioprobe has promising application in biomedical fields.

Dual-emissive Polymer Dots for Rapid Detection of Fluoride in Pure Water and Biological Systems with Improved Reliability and Accuracy.

It is of paramount importance to develop new probes that can selectively, sensitively, accurately and rapidly detect fluoride in aqueous media and biological systems, because F- is found to be closely related to many health and environmental concerns. Herein, a dual-emissive conjugated polyelectrolyte P1 containing phosphorescent iridium(III) complex was designed and synthesized, which can form ultrasmall polymer dots (Pdots) in aqueous media. The F--responsive tert-butyldiphenylsilyl moiety was introduced into iridium(III) complex as the signaling unit for sensing F− with the quenched phosphorescence. Thus, the dual-emissive Pdots can rapidly and accurately detect F− in aqueous media and live cells as a ratiometric probe by measuring the change in the ratio of the F−-sensitive red phosphorescence from iridium(III) complex to the F−-insensitive blue fluorescence from polyfluorene. Moreover, the interaction of Pdots with F− also changes its emission lifetime, and the lifetime-based detection of F− in live cells has been realized through photoluminescence lifetime imaging microscopy for the first time. Both the ratiometric luminescence and lifetime imaging have been demonstrated to be resistant to external influences, such as the probe’s concentration and excitation power. This study provides a new perspective for the design of promising Pdots-based probes for biological applications.

Dual-Emissive Nanohybrid for Ratiometric Luminescence and Lifetime Imaging of Intracellular Hydrogen Sulfide

We design a nanohybrid for the detection of hydrogen sulfide (H2S) based on mesoporous silica nanoparticles (MSNs). A phosphorescent iridium(III) complex and a specific H2S-sensitive merocyanine derivative are embedded into the nanohybrid. It exhibits a unique dual emission that is ascribed to the iridium(III) complex and the merocyanine derivative, respectively. Upon addition of sodium hydrogen sulfide (NaHS), the emission from the merocyanine derivative is quenched, while the emission from the iridium(III) complex is almost unchanged, which enables the ratiometric detection of H2S. Additionally, the nanohybrid has a long luminescence lifetime and displays a significant change in luminescence lifetime in response to H2S. Intracellular detection of H2S is performed via ratiometric imaging and photoluminescence lifetime imaging microscopy. Compared with the intensity-based method, the lifetime-based detection is independent of the probe concentration and can efficiently distinguish the signals of the probe from the autofluorescence in complex biological samples.

p–n Metallophosphor based on cationic iridium(III) complex for solid-state light-emitting electrochemical cells

An ionic transition-metal complex for improved charge transporting properties was designed, containing both n-type dimesitylboryl (BMes2) and p-type carbazole groups. The complex, [Ir(Bpq)2(CzbpyCz)]PF6 (1) (Bpq = 2-[4-(dimesitylboryl)phenyl] quinoline, CzbpyCz = 5,5′-bis(9-hexyl-9H-carbazol-3-yl)-2,2′-bipyridine) and its equivalent in which the BMes2 groups were substituted with carbazole moieties were evaluated on the photoluminescence and excited state properties in detail. According to the photophysical and electrochemical properties, we concluded that the BMes2 groups can increase the conjugation length of the cyclometalated C^N ligands and greatly enhance the phosphorescence efficiency over the carbazole groups. In addition, the bulky BMes2 groups are effective in preventing the molecular aggregation in film. Both complexes were used to prepare single component light-emitting electrochemical cells (LECs). The electroluminescent devices show the typical behavior of LECs. The LEC based on the complex containing both electron- and hole-transporting groups shows the best performance. This work demonstrated that the design and synthesis of p–n metallophosphors will be beneficial for the improvement of device performances.

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.

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.

Phosphorescence switch and logic gate of iridium(III) complexes containing a triarylboron moiety triggered by fluoride and an electric field

A new concept of phosphorescence switch and logic gate has been proposed based on iridium(III) complexes containing triarylboron moieties. The phosphorescence of the complexes can be quenched by F− through the formation of B–F bonds. Interestingly, the B–F bonds can be ruptured under an electric field, restoring the phosphorescence.