Xunjin Zhu

Water-Soluble Mitochondria-Specific Ytterbium Complex with Impressive NIR Emission

A water-soluble porphyrinato ytterbium complex linked with rhodamine B (Yb-2) showed mitochondria-specific subcellular localization and strong two-photon-induced NIR emissions (λ(em) = 650 nm, porphyrinate ligand π → π* transition; λ(em) = 1060 nm, Yb(III) (5)F(5/2) → (5)F(7/2) transitions; σ(2) = 375 GM in DMSO) with an impressive Yb(III) NIR emission quantum yield (1% at λ(ex) = 340 nm; 2.5% at λ(ex) = 430 nm) in aqueous solution.

Molecular Engineering of Simple Phenothiazine-Based Dyes To Modulate Dye Aggregation, Charge Recombination, and Dye Regeneration in Highly Efficient Dye-Sensitized Solar Cells

A series of simple phenothiazine-based dyes, namely, TP, EP, TTP, ETP, and EEP have been developed, in which the thiophene (T), ethylenedioxythiophene (E), their dimers, and mixtures are present to modulate dye aggregation, charge recombination, and dye regeneration for highly efficient dye-sensitized solar cell (DSSC) applications. Devices sensitized by the dyes TP and TTP display high power conversion efficiencies (PCEs) of 8.07 (Jsc = 15.2 mA cm(-2), Voc =0.783 V, fill factor (FF) = 0.679) and 7.87 % (Jsc = 16.1 mA cm(-2), Voc = 0.717 V, FF = 0.681), respectively; these were measured under simulated AM 1.5 sunlight in conjunction with the I(-)/I3(-) redox couple. By replacing the T group with the E unit, EP-based DSSCs had a slightly lower PCE of 7.98 % with a higher short-circuit photocurrent (Jsc) of 16.7 mA cm(-2). The dye ETP, with a mixture of E and T, had an even lower PCE of 5.62 %. Specifically, the cell based on the dye EEP, with a dimer of E, had inferior Jsc and Voc values and corresponded to the lowest PCE of 2.24 %. The results indicate that the photovoltaic performance can be finely modulated through structural engineering of the dyes. The selection of T analogues as donors can not only modulate light absorption and energy levels, but also have an impact on dye aggregation and interfacial charge recombination of electrons at the interface of titania, electrolytes, and/or oxidized dye molecules; this was demonstrated through DFT calculations, electrochemical impedance analysis, and transient photovoltage studies.

Conformational engineering of co-sensitizers to retard back charge transfer for high-efficiency dye-sensitized solar cells

We demonstrate that the post-adsorption of small molecules (a phenothiazine-based dye) on the porphyrin-sensitized TiO2 anode surface plays dual roles: (1) to greatly retard the back reaction between conduction-band electrons in TiO2 and the oxidized species (I3−) in the electrolyte and (2) to enhance the spectral response of solar cells. These two effects finally give rise to device efficiencies exceeding 10%, which are superior to those of individual dye-sensitized devices by either porphyrin (7.4%) or phenothiazine (8.2%) under the same conditions. Experimental analyses show that the incoming small molecules are adsorbed in the interstitial site of porphyrin dyes, forming densely surface packed molecules and thus impeding the I3− species from approaching the TiO2 surface. Since a broad range of ruthenium-based dyes and porphyrin-based photosensitizers possess relatively large molecular volumes, this method is anticipated to be applicable for further improving the energy conversion efficiency of devices sensitized by these two classes of dyes.

New Co(OH)2/CdS nanowires for efficient visible light photocatalytic hydrogen production

Through a facile impregnation synthesis, new noble-metal-free Co(OH)2/CdS nanowires (NWs) have been developed for photocatalytic hydrogen production. The loading of Co(OH)2 on CdS NWs can effectively accelerate the charge separation and transfer in photocatalytic reactions, leading to an enhanced H2 production rate (HPR). The optimum HPR based on Co(OH)2/CdS reaches 14.43 mmol h−1 g−1 under visible light (λ ≥ 420 nm) irradiation, which is 206 times higher than for the pristine CdS NWs and even 3 times higher than for 1 wt% Pt/CdS NWs as a benchmark. Impressively, core–shell structural Co(OH)2/CdS NWs formed by visible-light-induced self-assembly during the photocatalytic reaction. And the core–shell structural characteristics of the Co(OH)2/CdS NWs can effectively avoid light corrosion, leading to a stable HPR in 12 hours duration.

New phosphorescent platinum(II) Schiff base complexes for PHOLED applications

Some new symmetric and asymmetric platinum(II) Schiff base complexes with bulky substituents such as tert-butyl and triphenylamino groups have been synthesized which effectively reduced the aggregation or excimer formation. Using selected complexes as phosphorescent emitting materials, yellow light-emitting devices were fabricated with improved efficiency compared with the previously reported analogues. In addition, the phosphorescent white organic light-emitting device (WOLED) was fabricated using a single emissive layer composed of yellow- and blue-emitting materials.

Light‐Harvesting Ytterbium(III)–Porphyrinate–BODIPY Conjugates: Synthesis, Excitation‐Energy Transfer, and Two‐Photon‐Induced Near‐Infrared‐Emission Studies

Based on a donor-acceptor framework, several conjugates have been designed and prepared in which an electron-donor moiety, ytterbium(III) porphyrinate (YbPor), was linked through an ethynyl bridge to an electron-acceptor moiety, boron dipyrromethene (BODIPY). Photoluminescence studies demonstrated efficient energy transfer from the BODIPY moiety to the YbPor counterpart. When conjugated with the YbPor moiety, the BODIPY moiety served as an antenna to harvest the lower-energy visible light, subsequently transferring its energy to the YbPor counterpart, and, consequently, sensitizing the Yb(III) emission in the near-infrared (NIR) region with a quantum efficiency of up to 0.73% and a lifetime of around 40 μs. Moreover, these conjugates exhibited large two-photon-absorption cross-sections that ranged from 1048-2226 GM and strong two-photon-induced NIR emission.

Phosphorescent Cu(I) complexes based on bis(pyrazol-1-yl-methyl)-pyridine derivatives for organic light-emitting diodes†

Mononuclear Cu(I) complexes based on bis(pyrazol-1-yl-methyl)-pyridine derivatives and ancillary triphenylphosphine have been prepared and characterized by 1H NMR, mass spectroscopy and single-crystal X-ray analysis. The thermogravimetric analysis shows that the complexes exhibit high thermal stability. The electronic absorption spectra display two features in the regions of 230–260 and 290–350 nm attributable to mixed ligand-to-ligand (LLCT) and metal-to-ligand-charge-transfer (MLCT) excited states, which is supported by the results of density functional theory (DFT) and time-dependent DFT (TDDFT) calculations on these Cu(I) complexes. These complexes are strongly emissive in the solid state at ambient temperature. Intense blue or green emission in the poly(methyl methacrylate) film is observed in the region of 475–518 nm for these complexes with the emission lifetimes in the microsecond time scale (12–20 μs), indicating that the emission may be phosphorescence emission. Increasing the steric hindrance of the substituents on the pyrazole unit results in a blue-shift of the emission bands and enhanced emission quantum efficiency in PMMA films. The two most emissive complexes have been used for the fabrication of phosphorescent organic light-emitting diodes (POLEDs).

Effects of various π-conjugated spacers in thiadiazole[3,4-c]pyridine-cored panchromatic organic dyes for dye-sensitized solar cells

A series of new metal-free panchromatic organic photosensitizers based on a strong electron-deficient thiadiazole[3,4-c]pyridine core has been prepared and applied in dye-sensitized solar cells. The incorporation of the auxiliary thiadiazole[3,4-c]pyridine unit can effectively adjust the HOMO and LUMO energy levels, to design small band-gap photosensitizers with panchromatic absorption. The impacts of various π-conjugated spacers on the absorption properties, electrochemical properties and photovoltaic performances have been investigated systematically. The sensitizer Y3 with a benzene unit adjacent to the anchoring cyanoacrylic group produces a higher photocurrent and photovoltage in cell performance, as compared to Y1 and Y2 with thiophene and n-hexylthiophene unit adjacent to the anchoring group, respectively. Further structural optimization in Y4 with a n-hexylthiophene π-conjugated spacer inserted between the donor and thiadiazole[3,4-c]pyridine core results in the best photovoltaic performance. For comparison, the sensitizer Y5 with thiophene instead of n-hexylthiophene in the molecule exhibits the most inferior performance; this demonstrates that the long alkyl chains can effectively improve the cell performance by suppressing the dye aggregation on TiO2 film, enhancing electron injection efficiency, and retarding charge recombination by shielding the surface of TiO2 from I3− ions. The overall conversion efficiency of liquid–electrolyte DSSC based on Y4 shows the highest efficiency of 6.30% with a short-circuit photocurrent density (Jsc) of 12.54 mA cm−2, an open-circuit photovoltage (Voc) of 0.749 V, and a fill factor (FF) of 0.671, under standard global AM 1.5 solar light condition. Density functional theory calculations and electrochemical impedance spectroscopy analysis of these sensitizers provide further insight into the molecular geometry and the impact of the different π-conjugated spacers on the photophysical and photovoltaic performance.

A novel bifunctional mitochondria-targeted anticancer agent with high selectivity for cancer cells

Mitochondria have recently emerged as novel targets for cancer therapy due to its important roles in fundamental cellular function. Discovery of new chemotherapeutic agents that allow for simultaneous treatment and visualization of cancer is urgent. Herein, we demonstrate a novel bifunctional mitochondria-targeted anticancer agent (FPB), exhibiting both imaging capability and anticancer activity. It can selectively accumulate in mitochondria and induce cell apoptosis. Notably, it results in much higher toxicity toward cancer cells owing to much higher uptake by cancer cells. These features make it highly attractive in cancer imaging and treatment.

Pure white-light and colour-tuning of Eu3+-Gd3+-containing metallopolymer

Direct white-light (CIE coordinate of x = 0.333, y = 0.335, CCT of 5455 K and CRI of 82) with a high luminous efficiency (18.4%) was achieved in the first example of Eu(3+)-Gd(3+)-containing metallopolymer Poly(2-co-NVK-co-4), which also showed tunable purplish-blue to white to yellow-green photoluminescence.