Highly Efficient Organic Solar Cells with Improved Vertical Donor-Acceptor Compositional Gradient Via an Inverted Off-Center Spinning Method.

A novel, yet simple solution fabrication technique to address the trade-off between photocurrent and fill factor in thick bulk heterojunction organic solar cells is described. The inverted off-center spinning technique promotes a vertical gradient of the donor-acceptor phase-separated morphology, enabling devices with near 100% internal quantum efficiency and a high power conversion efficiency of 10.95%.

Aptamer loaded MoS2 nanoplates as nanoprobes for detection of intracellular ATP and controllable photodynamic therapy.

In this work we designed a MoS2 nanoplate-based nanoprobe for fluorescence imaging of intracellular ATP and photodynamic therapy (PDT) via ATP-mediated controllable release of (1)O2. The nanoprobe was prepared by simply assembling a chlorine e6 (Ce6) labelled ATP aptamer on MoS2 nanoplates, which have favorable biocompatibility, unusual surface-area-to-mass ratio, strong affinity to single-stranded DNA, and can quench the fluorescence of Ce6. After the nanoprobe was internalized into the cells and entered ATP-abundant lysosomes, its recognition to ATP led to the release of the single-stranded aptamer from MoS2 nanoplates and thus recovered the fluorescence of Ce6 at an excitation wavelength of 633 nm, which produced a highly sensitive and selective method for imaging of intracellular ATP. Meanwhile, the ATP-mediated release led to the generation of (1)O2 under 660 nm laser irradiation, which could induce tumor cell death with a lysosomal pathway. The controllable PDT provided a model approach for design of multifunctional theranostic nanoprobes. These results also promoted the development and application of MoS2 nanoplate-based platforms in biomedicine.

Folate receptor-targeted and cathepsin B-activatable nanoprobe for in situ therapeutic monitoring of photosensitive cell death.

The integration of diagnostic and therapeutic functions in a single system holds great promise to enhance the theranostic efficacy and prevent the under- or overtreatment. Herein, a folate receptor-targeted and cathepsin B-activatable nanoprobe is designed for background-free cancer imaging and selective therapy. The nanoprobe is prepared by noncovalently assembling phospholipid-poly(ethylene oxide) modified folate and photosensitizer-labeled peptide on the surface of graphene oxide. After selective uptake of the nanoprobe into lysosome of cancer cells via folate receptor-mediated endocytosis, the peptide can be cleaved to release the photosensitizer in the presence of cancer-associated cathepsin B, which leads to 18-fold fluorescence enhancement for cancer discrimination and specific detection of intracellular cathepsin B. Under irradiation, the released photosensitizer induces the formation of cytotoxic singlet oxygen for triggering photosensitive lysosomal cell death. After lysosomal destruction, the lighted photosensitizer diffuses from lysosome into cytoplasm, which provides a visible method for in situ monitoring of therapeutic efficacy. The nanoprobe exhibits negligible dark toxicity and high phototoxicity with the cell mortality rate of 0.06% and 72.1%, respectively, and the latter is specific to folate receptor-positive cancer cells. Therefore, this work provides a simple but powerful protocol with great potential in precise cancer imaging, therapy, and therapeutic monitoring.

Highly fluorescent, near-infrared-emitting Cd²âº-tuned HgS nanocrystals with optical applications.

Bulk HgS itself has proven to be a technologically important material; however, the poor stability and weak emission of HgS nanocrystals have greatly hindered their promising applications. Presently, a critical problem is the uncontrollable growth of HgS NCs and their intrinsic surface states which are susceptible to the local environment. Here, we address the issue by an ion-tuning approach to fabricating stable, highly fluorescent Cd:HgS/CdS NCs for the first time, which efficiently tuned the band-gap level of HgS NCs, pushing their intrinsic states far away from the surface, reducing the strong interaction of the environment with surface states and hence drastically boosting the exciton transition. As compared to bare HgS NCs, the obtained Cd:HgS/CdS NCs exhibited tunable luminescence peaks from 724 to 825 nm with an unprecedentedly high quantum yield up to 40% at room temperature and excellent thermal and photostability. Characterized by TEM, XRD, XPS, and AAS, the resultant Cd:HgS/CdS NCs possessed a zinc-blende structure and was composed of a homogeneous alloyed HgCdS structure coated with a thin-layer CdS shell. The formation mechanism of Cd:HgS/CdS NCs was proposed. These bright, stable HgS-based NCs presented promising applications as fluorescent inks for anticounterfeiting and as excellent light converters when coated onto a blue-light-emitting diode.

A pH-activatable and aniline-substituted photosensitizer for near-infrared cancer theranostics.

This work reports a newly designed pH-activatable and aniline-substituted aza-boron-dipyrromethene as a trifunctional photosensitizer to achieve highly selective tumor imaging, efficient photodynamic therapy (PDT) and therapeutic self-monitoring through encapsulation in a cRGD-functionalized nanomicelle. The diethylaminophenyl is introduced in to the structure for pH-activatable near-infrared fluorescence and singlet oxygen (1O2) generation, and bromophenyl is imported to increase the 1O2 generation efficiency upon pH activation by virtue of its heavy atom effect. After encapsulation, the nanoprobe can target αvß3 integrin-rich tumor cells via cRGD and is activated by physiologically acidic pH for cancer discrimination and PDT. The fascinating advantage of the nanoprobe is near-infrared implementation beyond 800 nm, which significantly improves the imaging sensitivity and increases the penetration depth of the PDT. By monitoring the fluorescence decrease in the tumor region after PDT, the therapeutic efficacy is demonstrated in situ and in real time, which provides a valuable and convenient self-feedback function for PDT efficacy tracking. Therefore, this rationally designed and carefully engineered nanoprobe offers a new paradigm for precise tumor theranostics and may provide novel opportunities for future clinical cancer treatment.

How do nitrogen-doped carbon dots generate from molecular precursors? An investigation of the formation mechanism and a solution-based large-scale synthesis.

A bottom-up method, using monoethanolamine (MEA) as both a passivation agent and a solvent, has been developed for rapid and massive synthesis of nitrogen-doped carbon dots (N-C-dots) from citric acid under heating conditions. This method requires a relatively mild temperature (170 °C) without special equipment, and affords one-pot large-scale production (39.96 g) of high-quality N-C-dots (quantum yield of 40.3%) in a few minutes (10 minutes). Significantly, an interesting formation process of N-C-dots, for the first time, has been monitored by transmission electron microscopy, ultraviolet-visible absorbance spectroscopy, photoluminescence spectroscopy, Fourier transformed infrared spectroscopy, and thermogravimetric analysis, and a corresponding formation mechanism, including polymerization, aromatization, nucleation, and growth, is proposed. It is important that the MEA-based synthesis of N-C-dots can be extended to various precursors, such as glucose, ascorbic acid, cysteine, and glutathione, which show general universality. Furthermore, the N-C-dots with strong fluorescence, excellent optical stability, and low cytotoxicity are successfully applied as fluorescent probes for bioimaging.

Ultra-bright near-infrared-emitting HgS/ZnS core/shell nanocrystals for in vitro and in vivo imaging.

Near-infrared (NIR)-emitting nanocrystals have enormous potential as an enabling technology for applications ranging from tunable infrared lasers to biological labels. Mercury chalcogenide NCs are one of the attractive NCs with NIR emission; however, the potential toxicity of Hg restricts their diverse applications. Herein, we synthesized low-toxic, highly luminescent and stable GSH-capped HgS/ZnS core/shell NCs by an aqueous route for the first time. The core/shell structure was characterized by using TEM, XRD and XPS, which provide evidence for the shell growth. After the successful growth of an appropriate ZnS shell around HgS NCs, poorly luminescent HgS NCs converted into ultra-bright HgS/ZnS NCs, substantially increasing photoluminescence quantum yield up to 43.8% at room temperature. The fluorescence peak of HgS/ZnS NCs was successfully tuned in a wide NIR window ranging from 785 nm to 1060 nm with high emission efficiency by controlling the synthetic pH values. Significantly, an in vitro cytotoxicity study clearly demonstrated that the HgS/ZnS NCs exhibited good biocompatibility as evidenced by the cell viability retained above 80% at a dose of HgS/ZnS NCs up to 150 µg mL-1. More importantly, the low-toxic NIR-emitting HgS/ZnS NCs have proved to be an effective fluorescent label in in vitro and in vivo imaging. The penetration depth reached 2 cm in a nude mouse with distinct separation of autofluorescence and NCs' fluorescence, giving excellent contrast at all depths. The novel highly-luminescent NIR-emitting HgS/ZnS NCs open up new possibilities for highly-sensitive, highly spectrally resolved and multicolor imaging in biomedical applications.

A multifunctional nanomicelle for real-time targeted imaging and precise near-infrared cancer therapy.

Simultaneous targeted cancer imaging, therapy and real-time therapeutic monitoring can prevent over- or undertreatment. This work describes the design of a multifunctional nanomicelle for recognition and precise near-infrared (NIR) cancer therapy. The nanomicelle encapsulates a new pH-activatable fluorescent probe and a robust NIR photosensitizer, R16FP, and is functionalized with a newly screened cancer-specific aptamer for targeting viable cancer cells. The fluorescent probe can light up the lysosomes for real-time imaging. Upon NIR irradiation, R16FP-mediated generation of reactive oxygen species causes lysosomal destruction and subsequently trigger lysosomal cell death. Meanwhile the fluorescent probe can reflect the cellular status and in situ visualize the treatment process. This protocol can provide molecular information for precise therapy and therapeutic monitoring.

Integrated molecular, interfacial, and device engineering towards high-performance non-fullerene based organic solar cells.

High-performance non-fullerene OSCs with PCEs of up to ca. 6.0% are demonstrated based on PBDTT-F-TT polymer and a molecular di-PBI acceptor through comprehensive molecular, interfacial, and device engineering. Impressive PCEs can also be retained in devices with relatively thick BHJ layer and processed through non-halogenated solvents, indicating these high-performance non-fullerene OSCs are promising for large-area printing applications.

Cell-specific and pH-activatable rubyrin-loaded nanoparticles for highly selective near-infrared photodynamic therapy against cancer.

Spatiotemporal control of singlet oxygen ((1)O2) release is a major challenge for photodynamic therapy (PDT) against cancer with high therapeutic efficacy and minimum side effects. Here a selenium-rubyrin (NMe2Se4N2)-loaded nanoparticle functionalized with folate (FA) was designed and synthesized as an acidic pH-activatable targeted photosensitizer. The nanoparticles could specifically recognize cancer cells via the FA-FA receptor binding and were selectively taken up by cancer cells via receptor-mediated endocytosis to enter lysosomes, in which NMe2Se4N2 was activated to produce (1)O2. The pH-controllable release of (1)O2 specially damaged the lysosomes and thus killed cancer cells in a lysosome-associated pathway. The introduction of selenium into the rubyrin core enhanced the (1)O2 generation efficiency due to the heavy atom effect, and the substitution of dimethylaminophenyl moiety at meso-position led to the pH-controllable activation of NMe2Se4N2. Under near-infrared (NIR) irradiation, NMe2Se4N2 possessed high singlet oxygen quantum yield (ΦΔ) at an acidic pH (ΦΔ = 0.69 at pH 5.0 at 635 nm) and could be deactivated at physiological pH (ΦΔ = 0.06 at pH 7.4 at 635 nm). The subcellular location-confined pH-activatable photosensitization at NIR region and the cancer cell-targeting feature led to excellent capability to selectively kill cancer cells and prevent the damage to normal cells, which greatly lowered the side effects. Through intravenous injection of FA-NMe2Se4N2 nanoparticles in tumor-bearing mice, tumor elimination was observed after NIR irradiation. This work presents a new paradigm for specific PDT against cancer and provides a new avenue for preparation of highly efficient photosensitizers.

[Spectra characteristics and electroluminescence performance of novel fluorene derivatives with aggregation fluorescence enhancement].

The photoluminescence (PL) spectra and UV-Visible absorption spectra of three novel fluorene derivatives solution containing different triphenylamine (TPA) and tetraphenyl-benzene (TPB) groups were systematically investigated. The PL spectra of the acetone/water solution were tested to analyze the capability of suppression concentration quenching (SCQ). The results showed that when water fraction ranged from 50% to 90%, the spectral irradiance of the mixture was obviously increased. Meanwhile, the PL spectra had blue shift due to the blue crystalline aggregation of novel fluorene derivatives, and the blue shift is proportional to the order of crystalline aggregation. Moreover, since the tetraphenyl-benzene and triphenylamine functional groups were tailored to fluorene backbone to suppress the concentration quenching of the fluorene dye and improve the charge carrier transporting ability, the non-doped organic light-emitting devices (OLEDs) were achieved.

[Spectral characteristics of white organic light-emitting devices based on phosphorescent system of three iridium chelates].

A white organic light-emitting device (WOLED) with a yellow phosphorescence material, bis[2-(4-tertbutylphenyl) benzothiazolato-N,C2 '] iridium (acetylacetonate) [(t-bt)2Ir(acac)], and two blue phosphorescence materials, iridium(Ill) bis (4', 6'-difluorophenylpyridinato) tetrakis(1-pyrazolyl) borate (FIr6) and bis[(4, 6-difluorophenyl)-pyridinato-N, C2 '] (picolinate) iridium (III) (FIrpic), were fabricated. Stable white emission was realized by using undoped ultrathin yellow emissive layer (EML), two doped blue EMLs together with the proper thickness of an interlayer confining the exciton. The WOLED performed pure white light emission with the Commissions Internationale de l'Eclairage (CIE) coordinates of (0.29+/-0.01, 0.34+/-0.01) from 6 to 14 V. Moreover, electroluminescence (EL) characteristics of the devices were also studied to verify the emissive mechanism from a phosphorescent system consisting of three iridium chelates. Also, the results showed that the triple-phosphor-element EMLs WOLED had lower efficiency roll-off owing to the stable recombination zone.

Transfer from trap emission to band-edge one in water-soluble CdS nanocrystals.

A simple and rapid route to water-soluble CdS nanocrystals stabilized by citrate was reported, and the transfer of citrate-stabilized CdS NCs from trap emission to band-edge one was studied systematically for the first time. It was found that heating in air, alkaline activation and illumination, all efficiently manipulated surface states of CdS NCs and controlled the emission states, leading to transferring CdS NCs from a broad trap emission (FWHM ~125 nm) to their strong, narrow band-gap emission (FWHM ~25 nm), comparable to that of CdS NCs synthesized by organic routes. Lifetime decay kinetic studies demonstrated that the average lifetimes for CdS NCs before and after transferred were 131.1 and 32.7 ns, respectively. The freshly-synthesized NCs were predominated by trap emission (~94%), while the transferred CdS NCs with well cubic structure dominated by band-edge emission (up to 91%). The tunable emissions of CdS NCs from violet to green could be achieved by controlling emission states of CdS NCs with different Cd/S molar ratios. The transfer mechanisms of CdS NCs from trap to band-edge emission were proposed to be epitaxial growth of a Cd(OH)(2) shell on CdS NCs core. The transition probability of energy states before and after transferred was further investigated.

Aqueous synthesis and characterization of glutathione-stabilized ß-HgS nanocrystals with near-infrared photoluminescence.

A simple, rapid and green aqueous approach to near-infrared (NIR)-emitting ß-HgS nanocrystals (NCs) was demonstrated for the first time by using glutathione (GSH) as the stabilizer at room temperature. The resulting HgS NCs with zinc blend structure exhibited strong quantum size effect, and the emission peak could be tuned in a wide NIR region from ca. 775 to 1041 nm. As compared with early achievements, the emission intensity of GSH-stabilized HgS NCs enhanced, with the maximum quantum yield reaching ~2.8%. It was also found that the stability of the GSH-HgS NCs was improved noticeably, the PL peak red-shifting only 9 nm and 23 nm after stored at 4°C for 4 months and 25°C for 7 days, respectively. The better stability of the HgS NCs was elucidated by FT-IR due to the multiple coordination of GSH molecule to surface Hg of the NCs. The emission range of GSH-stabilized HgS NCs was located between the visible region (500-800 nm) and IR region (1000-1600 nm) of HgS NCs as reported previously, extending the emission region of HgS nanomaterial. Therefore, the continuous emission from visible to IR spectral ranges provided HgS material more potential applications.

[Electroluminescent performance and spectral characteristics of a novel (t-bt)2Ir(acac) phosphorescent iridium complex].

The photoluminescence (PL) spectra and UV-Visible absorption spectra of a novel yellow phosphor dye of bis[2-(4-tert-butylphenyl)benzothiazolato-N,C2'] iridium (acetylacetonate) denoted as (t-bt)2Ir(acac) were systematically investigated, which were measured in solution and film states with various concentrations. The results showed that the highest PL intensity was achieved when the solution concentration was 3 x 10(-4) mol L(-1), and it decreased dramatically when the concentration kept on increasing because of concentration quenching of the phosphor dye. A red shift for PL spectra and UV-Vis absorption spectra of films compared to those of solutions were found, which is due to the shorter distance, aggregation effect, and stronger interaction of dye molecules in solid state. Based on the spectrum characterization, organic light-emitting diode was fabricated with an ultrathin structure based on this phosphor dye, which showed a high luminescence of 18 367 cd m(-2) at a bias of 13.2 V.

In situ synthesis of highly luminescent glutathione-capped CdTe/ZnS quantum dots with biocompatibility.

This paper focuses on the in situ synthesis of novel CdTe/ZnS core-shell quantum dots (QDs) in aqueous solution. Glutathione (GSH) was used as both capping reagent and sulfur source for in situ growth of ZnS shell on the CdTe core QDs. The maximum emission wavelengths of the prepared CdTe/ZnS QDs can be simply tuned from 569 nm to 630 nm. The PL quantum yield of CdTe/ZnS QDs synthesized is up to 84%, larger than the original CdTe QDs by around 1.7 times. The PL lifetime results reveal a triexponential decay model of exciton and trap radiation behavior. The average exciton lifetime at room temperature is 17.1 ns for CdTe (2.8 nm) and 27.4 ns for CdTe/ZnS (3.7 nm), respectively. When the solution of QDs is dialyzed for 3 h, 1.17 ppm of Cd(2+) is released from CdTe QDs and 0.35 ppm is released from CdTe/ZnS. At the dose of 120 microg/ml QDs, 9.5% of hemolysis was induced by CdTe QDs and 3.9% was induced by CdTe/ZnS QDs. These results indicate that the synthesized glutathione-capped CdTe/ZnS QDs are of less toxicity and better biocompatibility, so that are attractive for use in biological detection and related fields.

[Spectral characteristics of novel small molecular fluorene derivative for organic light-emitting device].

Double-layer organic light-emitting devices (OLEDs) based on a blend system of novel small molecule fluorene material 6,6'-(9H-fluoren-9,9-diyl) bis(2,3-bis(9,9-dihexyl-9H-fluoren-2-yl) quinoxaline) (BFLBBFLYQ) and hole transporting material N, N'-biphenyl-N, N'-bis-(3-methylphenyl)-1, 1'-biphenyl-4, 4'-diamine (TPD) were fabricated. The structure of the double-layer device was ITO/BFLBBFLYQ : TPD/tris(8-hydroxyquinolinato) aluminum(Alq)/Mg : Ag. The photoluminescence (PL) spectra of BFLBBFLYQ and TPD were located at 447 and 414 nm, respectively. The spectral characteristics of the blend system and the double-layer device were investigated, which indicated that a new long wavelength emission peaking at 530 nm was appeared both in PL spectra and electroluminescence (EL) spectra. The exciplex between BFLBBFLYQ and TPD may play the role in long wavelength emission in the blend device and the spin-coated film. Based on the absorption spectra of a red fluorescent dye 4-(dicyanomethylene)-2-tert-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as probe and the PL spectra of the blend system showing good overlap, energy transfer from the blend system to DCJTB could be expected. There fore, DCJTB could be selected as a molecular dopant to investigate the influence on EL spectra and the recombination of the devices. It was found that the excitons recombine at the interior Alq layer near to the BFLBBFLYQ : TPD layer.

[Influence of fluorescent dye ultrathin layer on luminescence spectra in organic light-emitting diodes].

By using an ultrathin dopant dye layer deposited on the top of host materials, the influence of concentration of three fluorescent dyes, dimethylquinacridone (DMQA), 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), and 5,6,11,12-tetraphenylnaphthacene (rubrene), on the luminescence spectra of OLEDs was studied. The characteristic of the brightness-efficiency-bias voltage performance was investigated. The results showed that compared to the conventional doping devices, the devices consisting of ultrathin dye layer exhibited a weak peak originating from host matrix, and the more obvious concentration quenching was existent. The degree of concentration quenching for the three ultrathin doping dyes from high to low is in the order of DMQA, DCJTB and rubrene. Meanwhile, the authors used the photoluminescence spectra of these three dopants dilute solution to testify the relationship between EL properties of OLEDs and concentration quenching of these dyes.

[Spectral characteristics of white organic light-emitting devices based on a novel nitrile fluorescence dye].

A white organic light-emitting device with a blend polymeric emissive system consisting of a novel nitrile fluorescence (2Z, 2'Z)-3, 3'-(1,4-phenylene)bis(2-phenylacrylonitrile) (BPhAN) as dopant and poly(N-vinylcarbazole) (PVK) as host was fabricated. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was introduced into bilayer device as an electron transporting layer (HTL) and a hole blocking layer (HBL), respectively. By adjusting the doping ratio of BPhAN, a series of devices with different concentration proportion of PVK : BPhAN were constructed. The photoluminescence (PL) and electroluminescence (EL) characteristics of the devices were systemically studied. The Förster energy transfer mechanisms and direct carrier trapping mechanisms were specially investigated. The results showed that effective Förster energy transfer from PVK to BPhAN existed in the blending system as well as carrier trapping. However, at the identical bias voltage, the performance of devices was affected mainly by the carrier trapping mechanisms. Nevertheless, at different bias voltages, the performance of devices was affected by both of the two mechanisms. When the doping ratio of BPhAN reached 4 wt%, bright white light was obtained. The peaks of EL spectra were located at 425 and 556 nm corresponding to the Commissions Internationale De L'Eclairage (CIE) coordinates of (0.33, 0.37) at 6 V and (0.32, 0.33) at 16 V, respectively. The slight shift of CIE coordinates was attributed to that energy transfer probability from PVK to BPhAN and BPhAN charge carrier trapping efficiency both decreased with the increase in voltages.

Selective synthesis of CdTe and high luminescence CdTe/CdS quantum dots: the effect of ligands.

This paper describes the selective syntheses of high luminescence CdTe and core-shell CdTe/CdS quantum dots (QDs) in aqueous solution by simple heating refluxing at 100 degrees C. CdTe QDs are prepared by using three kinds of ligands (thioglycolic acid-TGA, tiopronin-TP, and glutathione-GSH) as stabilizer, respectively. The results of refluxing for 10 min to several hours indicate that GSH-capped CdTe QDs have higher photoluminescence quantum yields (QY 54%) than TGA (QY 41%)- and TP (QY 24%)-stabilized CdTe QDs. Further, using TP-CdTe as core template and GSH as stabilizer and sulfur source, high luminescence GSH-capped CdTe/CdS core-shell QDs have been successfully synthesized in aqueous solution by simple refluxing at 100 degrees C. The GSH-CdTe/CdS QDs exhibit high fluorescence QYs about 55% over a broad spectral range of 530-588 nm, with the best QY of 83%. TP-stabilized CdTe/CdS QDs are also synthesized with TP as stabilizer and thioacetamide (TAA) as sulfur source, and with the best QY of 80%. GSH-stabilized CdTe and CdTe/CdS QDs are highly biocompatible, monodispersed, and stable under physiological conditions. The method of QDs prepared using GSH is simple and environmentally friendly, and it can be easily extended to the large-scale, aqueous-phase production of QDs.