Covalent Functionalization of Multi‐walled Carbon Nanotubes with a Gadolinium Chelate for Efficient T1‐Weighted Magnetic Resonance Imaging

Given the promise of carbon nanotubes (CNTs) for photothermal therapy, drug delivery, tissue engineering, and gene therapy, there is a need for non‐invasive imaging methods to monitor CNT distribution and fate in the body. In this study, non‐ionizing whole‐body high field magnetic resonance imaging (MRI) is used to follow the distribution of water‐dispersible non‐toxic functionalized CNTs administrated intravenously to mice. Oxidized CNTs are endowed with positive MRI contrast properties by covalent functionalization with the chelating ligand diethylenetriaminepentaacetic dianhydride (DTPA), followed by chelation to Gd³⁺. The structural and magnetic properties, MR relaxivities, cellular uptake, and application for MRI cell imaging of Gd‐CNTs in comparison to the precursor oxidized CNTs are evaluated. Despite the intrinsic T₂ contrast of oxidized CNTs internalized in macrophages, the anchoring of paramagnetic gadolinium onto the nanotube sidewall allows efficient T₁ contrast and MR signal enhancement, which is preserved after CNT internalization by cells. Hence, due to their high dispersibility, Gd‐CNTs have the potential to produce positive contrast in vivo following injection into the bloodstream. The uptake of Gd‐CNTs in the liver and spleen is assessed using MRI, while rapid renal clearance of extracellular Gd‐CNTs is observed, confirming the evidences of other studies using different imaging modalities.     

Design of Gold Nanoparticles for Magnetic Resonance Imaging

Improving the sensitivity of magnetic resonance imaging (MRI), a powerful non‐invasive medical imaging technique, requires the development of novel contrast agents with a higher efficiency than gadolinium chelates such as DTPA:Gd (DTPA: diethylenetriaminepentaacetic acid) that are currently used for clinical diagnosis. To achieve this objective, the strategy that we have explored involves the use of gold nanoparticles as carriers for gadolinium chelates. These nanoparticles are obtained by reducing a gold salt in the presence of a dithiolated derivative of DTPA. Characterization of these particles by transmission electron microscopy (TEM), X‐ray diffraction (XRD), thermogravimetric analysis (TGA), colorimetric titration, and X‐ray photoelectron spectroscopy (XPS) reveals the presence of a multilayered shell containing about 150 ligands on 2–2.5 nm sized particles. These particles exhibit a high relaxivity (r₁ = 585 mM ^–1 s^–1 as compared to 3.0 mM ^–1 s^–1 for DTPA:Gd), rendering them very attractive as contrast agents for MRI.     

Ultrasmall Water‐Soluble and Biocompatible Magnetic Iron Oxide Nanoparticles as Positive and Negative Dual Contrast Agents

Monodispersed water‐soluble and biocompatible ultrasmall magnetic iron oxide nanoparticles (UMIONs, D = 3.3 ± 0.5 nm) generated from a high‐temperature coprecipitation route are successfully used as efficient positive and negative dual contrast agents of magnetic resonance imaging (MRI). Their longitudinal relaxivity at 4.7 T (r₁ = 8.3 mM^?1 s^?1) is larger than that of clinically used T₁‐positive agent Gd‐DTPA (r₁ = 4.8 mM^?1 s^?1), and three times that of commercial contrast agent SHU‐555C (r₁ = 2.9 mM^?1 s^?1). The transversal relaxivity (r₂ = 35.1 mM^?1 s^?1) is six times that of Gd‐DTPA (r₂ = 5.3 mM^?1 s^?1), half of SHU‐555C (r₂ = 69 mM^?1 s^?1). The in vivo results show that the liver signal from T₁‐weighted MRI is positively enhanced 26%, and then negatively decreased 20% after injection of the iron oxide nanoparticles, which is stronger than those obtained from Gd‐DTPA (<10%) using the same dosage. The kidney signal is positively enhanced up to 35%, similar to that obtained from Gd‐DTPA. Under T₂‐weighted conditions, the liver signal is negatively enhanced ?70%, which is significantly higher than that from Gd‐DTPA (?6%). These results demonstrate the great potential of the UMIONs in dual contrast agents, especially as an alternative to Gd‐based positive contrast agents, which have risks of inducing side effects in patients.     

Multifunctional Nanoparticles Composed of A Poly( dl‐lactide‐coglycolide) Core and A Paramagnetic Liposome Shell for Simultaneous Magnetic Resonance Imaging and Targeted Therapeutics

A multifunctional nanoscale platform that is self‐assembled from a hydrophobic poly( dl ‐lactide‐coglycolide)(PLGA) core and a hydrophilic paramagnetic‐folate‐coated PEGylated lipid shell (PFPL; PEG=polyethylene glycol) is designed for simultaneous magnetic resonance imaging (MRI) and targeted therapeutics. The nanocomplex has a well‐defined core‐shell structure which is studied using confocal laser scanning microscopy (CLSM). The paramagnetic diethylenetriaminepentaacetic acid‐gadolinium (DTPA‐Gd) chelated to the shell layer exhibits significantly higher spin–lattice relaxivity (r₁) than the clinically used small‐molecular‐weight MRI contrast agent Magnevist^®. The PLGA core serves as a nanocontainer to load and release the hydrophobic drugs. From a drug‐release study, it is found that the modification of the PLGA core with a polymeric liposome shell can be a useful tool for reducing the drug‐release rate. Cellular uptake of folate nanocomplex is found to be higher than that of non‐folate‐nanocomplex due to the folate‐binding effect on the cell membrane. This work indicates that the multifunctional platform with combined characteristics applicable to MRI and drug delivery may have great potential in cancer chemotherapy and diagnosis.     

PEGylated Polypyrrole Nanoparticles Conjugating Gadolinium Chelates for Dual‐Modal MRI/Photoacoustic Imaging Guided Photothermal Therapy of Cancer

Polypyrrole nanoparticles conjugating gadolinium chelates were successfully fabricated for dual‐modal magnetic resonance imaging (MRI) and photoacoustic imaging guided photothermal therapy of cancer, from a mixture of pyrrole and pyrrole‐1‐propanoic acid through a facile one‐step aqueous dispersion polymerization, followed by covalent attachment of gadolinium chelate, using polyethylene glycol as a linker. The obtained PEGylated poly­pyrrole nanoparticles conjugating gadolinium chelates (Gd‐PEG‐PPy NPs), sized around around 70 nm, exhibited a high T₁ relaxivity coefficient of 10.61 L mm ^?1 s^?1, more than twice as high as that of the relating free Gd³⁺ complex (4.2 L mm ^–1 s^?1). After 24 h intravenous injection of Gd‐PEG‐PPy NPs, the tumor sites exhibited obvious enhancement in both T₁‐weighted MRI intensity and photoacoustic signal compared with that before injection, indicating the efficient accumulation of Gd‐PEG‐PPy NPs due to the introduction of the PEG layer onto the particle surface. In addition, tumor growth could be effectively inhibited after treatment with Gd‐PEG‐PPy NPs in combination with near‐infrared laser irradiation. The passive targeting and high MRI/photo­acoustic contrast capability of Gd‐PEG‐PPy NPs are quite favorable for precise cancer diagnosing and locating the tumor site to guide the external laser irradiation for photothermal ablation of tumors without damaging the surrounding healthy tissues. Therefore, Gd‐PEG‐PPy NPs may assist in better monitoring the therapeutic process, and contribute to developing more effective “personalized medicine,” showing great potential for cancer diagnosis and therapy.     

Water‐Soluble Polyfluorenes as an Interfacial Layer Leading to Cathode‐Independent High Performance of Organic Solar Cells

Novel poly[(9,9‐bis((6′‐(N,N,N‐trimethylammonium)hexyl)‐2,7‐fluorene)‐alt‐(9,9‐bis(2‐(2‐(2‐methoxyethoxy)ethoxy)ethyl)‐9‐fluorene)) dibromide (WPF‐6‐oxy‐F) and poly[(9,9‐bis((6′‐(N,N,N‐trimethylammonium)hexyl)‐2,7‐fluorene)‐alt‐(9,9‐bis(2‐(2‐methoxyethoxy)ethyl)‐fluorene)] dibromide (WPF‐oxy‐F) compounds are developed and the use of these water‐soluble polymers as an interfacial layer for low‐cost poly(3‐hexylthiophene):phenyl‐C₆₁ butyric acid methyl ester (P3HT:PCBM) organic solar cells (OSCs) is investigated. When WPF‐oxy‐F or WPF‐6‐oxy‐F is simply inserted between the active layer and the cathode as an interfacial dipole layer by spin‐coating water‐soluble polyfluorenes, the open‐circuit voltage (V_oc), fill factor (FF), and power‐conversion efficiency (PCE) of photovoltaic cells with high work‐function metal cathodes, such as Al, Ag, Au, and Cu, dramatically increases. For example, when WPF‐6‐oxy‐F is used with Al, Ag, Au, or Cu, regardless of the work‐function of the metal cathode, the V_oc is 0.64, 0.64, 0.58, and 0.63 V, respectively, approaching the original value of the P3HT:PCBM system because of the formation of large interfacial dipoles through a reduction of the metal work‐function. In particular, introducing WPF‐6‐oxy‐F into a low‐cost Cu cathode dramatically enhanced the device efficiency from 0.8% to 3.36%.     

Enhanced Relaxometric Properties of MRI “Positive” Contrast Agents Confined in Three‐Dimensional Cubic Mesoporous Silica Nanoparticles

Mesoporous silica nanoparticles (MSNs) are of growing interest for the development of novel probes enabling efficient tracking of cells in vivo using magnetic resonance imaging (MRI). The incorporation of Gd³⁺ paramagnetic ions into highly porous MSNs is a powerful strategy to synthesize “positive” MRI contrast agents for more quantitative T₁‐weighted MR imaging. Within this context, different strategies have been reported to integrate Gd chelates to 2D pore network MSNs. As an alternative, we report on the modulation of the pore network topology through the preparation of a 3D pore network hybrid GdSi_xO_y MSN system. In this study, 2D GdSi_xO_y‐MSNs with similar porosity and particle size were also prepared and the relaxometric performances of both materials, directly compared. Both syntheses lead to water‐dispersible MSNs suspensions (particle size < 200 nm), which were stable for at least 48h. 3D GdSi_xO_y‐MSNs provided a significant increase in ¹H longitudinal relaxivity (18.5 s^?1mM^?1; 4.6 times higher than Gd‐DTPA) and low r₂/r₁ ratios (1.56) compatible with the requirements of “positive” contrast agents for MRI. These results demonstrate the superiority of a 3D pore network to host paramagnetic atoms for MRI signal enhancement using T₁‐weighted imaging. Such an approach minimizes the total amount of paramagnetic element per particle.     

Solution‐Processed Thermally Activated Delayed Fluorescent OLED with High EQE as 31% Using High Triplet Energy Crosslinkable Hole Transport Materials

Solution‐processed organic light‐emitting diodes (OLEDs) with thermally activated delayed fluorescent (TADF) material as emitter have attracted much attention because of their low cost and high performance. However, exciton quench at the interface between the hole injection layer, poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and emitting layer (EML) in devices can lead to low device performance. Here, a novel high triplet energy (2.89 eV) and crosslinkable hole‐transporting material grafted with oxetane groups, N,N‐bis(4‐(6‐((3‐ethyloxetan‐3‐yl)methoxy)hexyloxy)phenyl)‐3,5‐di(9H‐carbazol‐9‐yl)benzenamine (Oxe‐DCDPA)), as crosslinked hole transport layer (HTL) into the interface of PEDOT:PSS layer and EML is proposed for prevention of exciton quenching, and among the reported devices with single HTL in solution‐processed TADF‐OLED, the highest external quantum efficiency (EQE)/luminous efficiency (η_L) of 26.1%/94.8 cd A^?1 and 24.0%/74.0 cd A^?1 are achieved for green emission (DACT‐II as emitter) and bluish‐green emission (DMAC‐TRZ as emitter), respectively. Further improvement, using double HTLs, composed of N,N′‐bis(4‐(6‐((3‐ethyloxetan‐3‐yl)methoxy))‐hexylphenyl)‐N,N′‐diphenyl‐4,4′‐diamine with high hole mobility and Oxe‐DCDPA with high triplet energy, leads to the highest EQE/η_L of 30.8%/111.9 cd A^?1 and 27.2%/83.8 cd A^?1 for green emission and bluish‐green emission, respectively. These two devices show the high maximum brightness of 81 100 and 70 000 cd m^?2, respectively.     

A DCM‐Type Red‐Fluorescent Dopant for High‐Performance Organic Electroluminescent Devices

2‐(2‐tert‐Butyl‐6‐((E)‐2‐(2,6,6‐trimethyl‐2,4,5,6‐tetrahydro‐1H‐pyrrolo[3,2,1‐ij]quinolin‐8‐yl)vinyl)‐4H‐pyran‐4‐ylidene)malononitrile (DCQTB) is designed and synthesized in high yield for application as the red‐light‐emitting dopant in organic light‐emitting diodes (OLEDs). Compared with 4‐(dicyanomethylene)‐2‐tert‐butyl‐6‐(1,1,7,7,‐tetramethyljulolidyl‐9‐enyl)‐4H‐pyran (DCJTB), one of the most efficient red‐emitting dopants, DCQTB exhibits red‐shifted fluorescence but blue‐shifted absorption. The unique characteristics of DCQTB with respect to DCJTB are utilized to achieve a red OLED with improved color purity and luminous efficiency. As a result, the device that uses DCQTB as dopant, with the configuration: indium tin oxide (ITO)/N,N′‐bis(1‐naphthyl)‐N,N′‐diphenyl‐1,1′‐biphenyl‐4,4′‐diamine (NPB; 60 nm)/tris(8‐quinolinolato) aluminum (Alq₃):dopant (2.3 wt %) (7 nm)/2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (BCP; 12 nm)/Alq₃(45 nm)/LiF(0.3 nm):Al (300 nm), shows a larger maximum luminance (L_max = 6021 cd m^–2 at 17 V), higher maximum efficiency (η_max = 4.41 cd A^–1 at 11.5 V (235.5 cd m^–2)), and better chromaticity coordinates (Commission Internationale de l'Eclairage, CIE, (x,y) = (0.65,0.35)) than a DCJTB‐based device with the same structure (L_max = 3453 cd m^–2 at 15.5 V, η_max = 3.01 cd A^–1 at 10 V (17.69 cd m^–2), and CIE (x,y) = (0.62,0.38)). The possible reasons for the red‐shifted emission but blue‐shifted absorption of DCQTB relative to DCJTB are also discussed.     

Cover Picture: Synthesis of Gadolinium‐Labeled Shell‐Crosslinked Nanoparticles for Magnetic Resonance Imaging Applications (Adv. Funct. Mater. 8/2005)

Robust, amphiphilic core–shell nanoparticles that are selectively labeled with gadolinium in the hydrophilic and water‐swollen shell layer are depicted in the cover picture. These well‐defined nanostructured materials exhibit high relaxivity, a large loading capacity, and are based upon a biocompatible platform for ultimate function in magnetic resonance imaging (MRI) applications, as reported by Wooley and co‐workers on p. 1248. Shell‐crosslinked knedel‐like nanoparticles (SCKs; “knedel” is a Polish term for dumplings) were derivatized with gadolinium chelates and studied as robust magnetic‐resonance‐imaging‐active structures with hydrodynamic diameters of 40 ± 3 nm. SCKs possessing an amphiphilic core–shell morphology were produced from the aqueous assembly of diblock copolymers of poly‐(acrylic acid) (PAA) and poly(methyl acrylate) (PMA), PAA₅₂–b–PMA₁₂₈, and subsequent covalent crosslinking by amidation upon reaction with 2,2′‐(ethylenedioxy)bis(ethylamine) throughout the shell layer. The properties of these materials, including non‐toxicity towards mammalian cells, non‐immunogenicity within mice, and capability for polyvalent targeting, make them ideal candidates for utilization within biological systems. The synthesis of SCKs derivatized with Gd^III and designed for potential use as a unique nanometer‐scale contrast agent for MRI applications is described herein. Utilization of an amino‐functionalized diethylenetriaminepentaacetic acid–Gd analogue allowed for direct covalent conjugation throughout the hydrophilic shell layer of the SCKs and served to increase the rotational correlation lifetime of the Gd. In addition, the highly hydrated nature of the shell layer in which the Gd was located allowed for rapid water exchange; thus, the resulting material demonstrated large ionic relaxivities (39 s^–1 mM^–1) in an applied magnetic field of 0.47 T at 40 °C and, as a result of the large loading capacity of the material, also demonstrated high molecular relaxivities (20 000 s^–1 mM^–1).     

Mesoporous Silica Nanoparticles: Selective Surface Functionalization for Optimal Relaxometric and Drug Loading Performances

Mesoporous silica nanoparticles (MSNs) have emerged as promising biomaterials for drug delivery and cell tracking applications, for which MRI is the medical imaging modality of choice. In this contribution, MRI contrast agents (DTPA‐Gd) and polyethylene glycol (PEG) are grafted selectively at the surface of MSNs, in order to achieve optimal relaxometric and drug loading performances. In fact, DTPA and PEG grafting procedures reported until now, have resulted in significant pore obstruction, which is detrimental to the drug delivery function of MSNs. This usually induces a dramatic decrease in surface area and pore volume, thus limiting drug loading capacity. Therefore, these molecules must be selectively grafted at the outer surface of MSNs. In this study, 3D pore network MSNs (MCM‐48‐type) are synthesized and functionalized with a straightforward and efficient grafting procedure in which DTPA and PEG are selectively grafted at the outer surface of MSNs. No pore blocking is observed, and more than 90% of surface area, pore volume and pore diameter are retained. The thus‐treated particles are colloidally stable in SBF and cell culture media, they are not cytotoxic and they have high drug loading capacity. Upon labeling with Gd, the nanoparticle suspensions have strong relaxometric properties (r₂/r₁ = 1.47, r₁ = 23.97 mM^?1 s^?1), which confers a remarkable positive contrast enhancement potential to the compound. The particles could serve as efficient drug carriers, as demonstrated with a model of daunorubicin submitted to physiological conditions. The selective nanoparticle surface grafting procedures described in the present article represent a significant advance in the design of high colloidal stability silica‐based vectors with high drug loading capacity, which could provide novel theranostic nanocompounds.     

Nanostructured Poly(styrene‐b‐butadiene‐b‐styrene) (SBS) Membranes for the Separation of Nitrogen from Natural Gas

The preparation and characterization of new, tailor‐made polymeric membranes using poly(styrene‐b‐butadiene‐b‐styrene) (SBS) triblock copolymers for gas separation are reported. Structural differences in the copolymer membranes, obtained by manipulation of the self‐assembly of the block copolymers in solution, are characterized using atomic force microscopy, transmission electron microscopy, and the transport properties of three gases (CO₂, N₂, and CH₄). The CH₄/N₂ ideal selectivity of 7.2, the highest value ever reported for block copolymers, with CH₄ permeability of 41 Barrer, is obtained with a membrane containing the higher amount of polybutadiene (79 wt%) and characterized by a hexagonal array of columnar polystyrene cylinders normal to the membrane surface. Membranes with such a high separation factor are able to ease the exploitation of natural gas with high N₂ content. The CO₂/N₂ ideal selectivity of 50, coupled with a CO₂ permeability of 289 Barrer, makes SBS a good candidate for the preparation of membranes for the post‐combustion capture of carbon dioxide.     

Synthesis of Gadolinium‐Labeled Shell‐Crosslinked Nanoparticles for Magnetic Resonance Imaging Applications

Shell‐crosslinked knedel‐like nanoparticles (SCKs; “knedel” is a Polish term for dumplings) were derivatized with gadolinium chelates and studied as robust magnetic‐resonance‐imaging‐active structures with hydrodynamic diameters of 40 ± 3 nm. SCKs possessing an amphiphilic core–shell morphology were produced from the aqueous assembly of diblock copolymers of poly‐(acrylic acid) (PAA) and poly(methyl acrylate) (PMA), PAA₅₂–b–PMA₁₂₈, and subsequent covalent crosslinking by amidation upon reaction with 2,2′‐(ethylenedioxy)bis(ethylamine) throughout the shell layer. The properties of these materials, including non‐toxicity towards mammalian cells, non‐immunogenicity within mice, and capability for polyvalent targeting, make them ideal candidates for utilization within biological systems. The synthesis of SCKs derivatized with Gd^III and designed for potential use as a unique nanometer‐scale contrast agent for MRI applications is described herein. Utilization of an amino‐functionalized diethylenetriaminepentaacetic acid–Gd analogue allowed for direct covalent conjugation throughout the hydrophilic shell layer of the SCKs and served to increase the rotational correlation lifetime of the Gd. In addition, the highly hydrated nature of the shell layer in which the Gd was located allowed for rapid water exchange; thus, the resulting material demonstrated large ionic relaxivities (39 s^–1 mM^–1) in an applied magnetic field of 0.47 T at 40 °C and, as a result of the large loading capacity of the material, also demonstrated high molecular relaxivities (20 000 s^–1 mM^–1).     

Pure‐Red Dye for Organic Electroluminescent Devices: Bis‐Condensed DCM Derivatives

In this paper, the bis‐condensed 4‐(dicyanomethylene)‐2‐methyl‐6‐[p‐(dimethylamino)styryl]‐4H‐pyran ( DCM) derivatives are introduced as a new class of red dye for organic light‐emitting devices (OLEDs). They showed more red‐shifted emission than the mono‐substituted DCM derivatives and the emission maxima increased as the electron‐donating ability of the aromatic donor group increased. On the basis of these results, red light‐emitting devices were fabricated with bis‐condensed DCM derivatives as red dopants. For a device of configuration ITO/TPD/Alq₃ + DADB (5.2 wt.‐%)/Alq₃/Al (where ITO is indium tin oxide, TPD is N,N′‐diphenyl‐N,N′‐bis(3‐methylphenyl)‐1,1′‐biphenyl‐4,4′‐diamine, Alq₃ is tris(8‐hydroxyquinoline) aluminum, and DADB is [2,6‐bis[2‐[5‐(dibutylamino)phenyl]vinyl]‐4H‐pyran‐4‐ylidene]propanedinitrile), pure red emission was observed with Commission Internationale de l’Eclairage (CIE 1931) coordinates of (0.658, 0.337) at 25 mA/cm².     

Quadratic Nonlinear Optical Properties of N‐Aryl Stilbazolium Dyes

The new salts trans‐4′‐(dimethylamino)‐N‐R‐4‐stilbazolium hexafluorophosphate (R = methyl, Me 1 , phenyl, Ph 2 , 2,4‐dinitrophenyl, DNPh 3 , 2‐pyrimidyl, Pym 4 , Scheme 1) have been prepared. Their electronic absorption spectra show intense, visible intramolecular charge‐transfer bands, the energy (E_max) of which decreases in the order R = Me > Ph > DNPh > Pym. This trend arises from the steadily increasing electron deficiency of the pyridinium ring, a phenomenon also observed in cyclic voltammetric and ¹H nuclear magnetic resonance (NMR) data. Fluorescence‐free first hyperpolarizability β values of [ 1 – 4 ]PF₆ were measured by using femtosecond hyper‐Rayleigh scattering (HRS) with acetonitrile solutions and a 1300 nm laser, and static first hyperpolarizabilities β₀ were obtained by application of the two‐state model. The HRS results indicate that the N‐aryl chromophores in [ 2 – 4 ]PF₆ have considerably larger β₀ values than their N‐methyl counterpart in [ 1 ]PF₆, with a ca. 10‐fold increase in β₀ observed in moving from [ 1 ]PF₆ to [ 4 ]PF₆ (25 → 230 × 10^–30 esu). Stark (electroabsorption) spectroscopic studies in butyronitrile glasses at 77 K allowed the derivation of dipole moment changes Δμ₁₂ (10.9–14.8 D), which have been used to calculate β₀ according to the two‐state equation β₀ = 3Δμ₁₂(μ₁₂)²/2(E_max)² (μ₁₂ = transition dipole moment). With the exception of [ 1 ]PF₆, the Stark‐derived β₀ values are in reasonable agreement with those from HRS. However, the increase in β₀ in moving from [ 1 ]PF₆ to [ 4 ]PF₆ is only 2‐fold for the Stark data (90 → 185 × 10^–30 esu). The observed trend of increasing β₀ in the order [ 1 ]PF₆ < [ 3 ]PF₆ < [ 2 ]PF₆ < [ 4 ]PF₆ arises from a combination of decreasing E_max and increasing Δμ₁₂, with only a slight increase in μ₁₂ between [ 1 ]PF₆ and [ 4 ]PF₆. It is likely that the β₀ values for [ 3 ]PF₆ are lower than expected due to the steric effect of the ortho‐NO₂ group, which causes twisting of the DNPh ring out of the plane of the stilbazolium unit. A single crystal X‐ray structure shows that [ 2 ]PF₆ crystallizes in the space group Cc, with head‐to‐tail alignment and almost parallel stacking of the pseudo‐planar stilbazolium portions of the cations to form polar sheets within a polar bulk structure. [ 2 ]PF₆ is essentially isostructural with the related Schiff base salt trans‐4‐[(4‐dimethylaminophenyl)iminomethyl]‐N‐phenylpyridinium hexafluorophosphate ([ 8 ]PF₆). Second harmonic generation (SHG) studies on [ 2 ]PF₆ and [ 8 ]PF₆ using a 1907 nm laser and sieved powdered samples (53–63 μm) afforded efficiencies of 470 and 240 times that of urea, respectively. Under the same conditions, the well‐studied compound [ 1 ]p‐MeC₆H₄SO₃ gave an SHG efficiency of 550 times that of urea.     

Morphological Evolution and Magnetic Property of Rare‐Earth‐Doped Hematite Nanoparticles: Promising Contrast Agents for T1‐Weighted Magnetic Resonance Imaging

A series of uniform rare‐earth‐doped hematite (α‐Fe₂O₃) nanoparticles are synthesized by a facile hydrothermal strategy. In a typical case of gadolinium (Gd)‐doped α‐Fe₂O₃, the morphology and chemical composition can be readily tailored by tuning the initial proportion of Gd³⁺/Fe³⁺ sources. As a result, the products are observed to be stretched into more elongated shapes with an increasing dopant ratio. As a benefit of such an elongated morphological feature and Gd³⁺ ions of larger effective magnetic moment than Fe³⁺, the doped product with the highest ratio of Gd³⁺ at 5.7% shows abnormal ferromagnetic features with a remnant magnetization of 0.605 emu g^?1 and a coercivity value of 430 Oe at 4 K. Density of states calculations also reveal the increase of total magnetic moment induced by Gd³⁺ dopant in α‐Fe₂O₃ hosts, as well as possible change of magnetic arrangement. As‐synthesized Gd‐doped α‐Fe₂O₃ nanoparticles are probed as contrast agents for T1‐weighted magnetic resonance imaging, achieving a remarkable enhancement effect for both in vitro and in vivo tests.     

Self‐Assembled Nanowires of Organic n‐Type Semiconductor for Nonvolatile Transistor Memory Devices

Organic nonvolatile transistor‐type memory (ONVM) devices are developed using self‐assembled nanowires of n‐type semiconductor, N,N′‐bis(2‐phenylethyl)‐perylene‐3,4:9,10‐tetracarboxylic diimide (BPE‐PTCDI). The effects of nanowire dimension and silane surface treatment on the memory characteristics are explored. The diameter of the nanowires is reduced by increasing the non‐solvent methanol composition, which led to the enhanced crystallinity and high field‐effect mobility. The BPE‐PTCDI nanowires with small diameters induce high electrical fields and result in a large memory window (the shifting of the threshold voltage, ΔV_th). The ΔV_th value of BPE‐PTCDI nanowire based ONVM device on the bare substrate can reach 51 V, which is significantly larger than that of thin film. The memory window is further enhanced to 78 V with the on/off ratio of 2.1 × 10⁴ and the long retention time (10⁴ s), using a hydrophobic surface (such as trichloro(phenyl)silane‐treated surface). The above results demonstrate that the n‐type semiconducting nanowires have potential applications in high performance non‐volatile transistor memory devices.     

Boosting the Efficiency of Near‐Infrared Fluorescent OLEDs with an Electroluminescent Peak of Nearly 800 nm by Sensitizer‐Based Cascade Energy Transfer

A sensitization‐based cascade energy transfer channel is proposed to boost the electroluminescent performances of the solution‐processed near‐infrared organic light‐emitting devices (OLEDs) featuring an electroluminescent peak of 786 nm from a new fluorescent emitter of N⁴,N⁴,N⁹,N⁹‐tetra‐p‐tolylnaphtho[2,3‐c][1,2,5]thiadiazole‐4,9‐diamine (NZ2mDPA) with unique aggregation‐induced emission (AIE) property. The optimized device is composed of 4,4′‐N,N‐dicarbazole‐biphenyl (CBP) as the host, bis(2‐phenyl‐1,3‐benzothiozolato‐N,C^2′)iridium (Ir(bt)₂(acac)) as the sensitizer, and NZ2mDPA as the emitter, where the cascade energy transfer can occur via two steps realizing unexpected triplet–singlet energy transfer by the Förster mechanism. The first step features efficient triplet harvesting from CBP to Ir(bt)₂(acac), and then the second step involves in resonant energy transfer from the phosphorescent sensitizer to the near‐infrared AIE emitter of NZ2mDPA, which finally endows two channels of harvesting singlet and triplet excitons. The unique scheme achieves not only more efficient Förster energy transfer but also the higher utilization efficiency of triplet excitons. As a result, the near‐infrared OLEDs can realize a factor of 2.7 enhancement of external quantum efficiency by employing the phosphor‐sensitized AIE lumogen compared with the commonly used binary host–guest system.     

Carbon Nanotube–Graphitic Carbon Nitride Hybrid Films for Flavoenzyme‐Catalyzed Photoelectrochemical Cells

In green plants, solar‐powered electrons are transferred through sophistically arranged photosystems and are subsequently channelled into the Calvin cycle to generate chemical energy. Inspired by the natural photosynthetic scheme, a photoelectrochemical cell (PEC) is constructed configured with protonated graphitic carbon nitride (p‐g‐C₃N₄) and carbon nanotube hybrid (CNT/p‐g‐C₃N₄) film cathode, and FeOOH‐deposited bismuth vanadate (FeOOH/BiVO₄) photoanode for the production of industrially useful chiral alkanes using an old yellow enzyme homologue from Thermus scotoductus (TsOYE). In the biocatalytic PEC platform, photoexcited electrons provided by the FeOOH/BiVO₄ photoanode are transferred to the robust and self‐standing CNT/p‐g‐C₃N₄ hybrid film that electrocatalytically reduces flavin mononucleotide (FMN) mediator. The p‐g‐C₃N₄ promotes a two‐electron reduction of FMN coupled with an accelerated electron transfer by the conductive CNT network. The reduced FMN subsequently delivers the electrons to TsOYE for the highly enantioselective conversion of ketoisophorone to (R)‐levodione. Under light illumination (>420 nm) and external bias, (R)‐levodione is synthesized with the enantiomeric excess value of above 83%, not influenced by the scale of applied bias, simultaneously exhibiting stable and high current efficiency. The results suggest that the biocatalytic PEC made up of economical materials can selectively synthesize high‐value organic chemicals using water as an electron donor.     

Perfluoroalkanoate‐Substituted PEDOT for Electrochromic Device Applications

The recent emergence of organic electrochromics on both the scientific and industrial levels has expedited the synthesis of new materials with varied electrochemical and optical properties. The structural versatility and broad usage of poly(3,4‐ethylenedioxythiophene) (PEDOT) has stimulated many research groups to focus on the potential of PEDOT derivatives. Here we report the first synthesis of pentadecafluoro‐octanoic acid 2,3‐dihydro‐thieno(3,4‐b)(1,4)dioxin‐2‐ylmethylester (EDOT‐F), along with its electrochemical polymerization, characterization, and incorporation into electrochromic devices (ECDs). PEDOT‐F is a cathodically coloring polymer that exhibits sub‐second switching time between a dark‐blue neutral state and a transmissive sky‐blue oxidized state, and expresses a 63 % change for both transmittance at λ_max and colorimetrically determined luminance. Hexafluorophosphate‐doped free‐standing films of PEDOT‐F possess conductivities of up to 65 S cm^–1. Variable transmittance ECDs constructed with PEDOT‐F and poly[3,6‐bis(2‐(3,4‐ethylenedioxythienyl))‐N‐methylcarbazole] (PBEDOT‐NMeCz) exhibit an optical contrast of 60 % at λ_max (580 nm) and an overall luminance change of 60 %. Indicating the hydrophobicity of this polymer, doped PEDOT‐F exhibits a water contact angle of 110°, significantly higher than the 30° exhibited for the doped PEDOT parent.