Sunwoo Kang

Thin‐Film Formation of Imidazolium‐Based Conjugated Polydiacetylenes and Their Application for Sensing Anionic Surfactants

Therehave been many exciting and significant results from theapplication of new imidazolium receptors to many anionictargets. Martnez-Mez et al. recently reported a colorimet-ric method for the selective determination of anionic surfac-tants using imidazolium-containing ionic liquids on a solidsupport.

A Chromo‐Fluorogenic Tetrazole‐Based CoBr2 Coordination Polymer Gel as a Highly Sensitive and Selective Chemosensor for Volatile Gases Containing Chloride

Crystalline coordination polymers are a newer class of organic–inorganic hybrid nanomaterials created by infinitely extending metal–ligand coordination interactions. These polymers show promise in a broad range of applications, including gas storage, molecular sieves, ion exchange, sensing, magnetism, and catalysis. [1, 2] Recently, a rational-design strategy for supramolecular gels based on the concept of coordination polymers is attracting interest. [3–6] In particular, recent studies have demonstrated that simple bridging organic units can facilitate the formation of coordination polymer gels in the absence of auxiliary moieties (e.g., urea, sugar, cholesterol, long alkyl chains), offering new possibilities to produce functional soft materials from structurally

Lysine-Functionalized Silver Nanoparticles for Visual Detection and Separation of Histidine and Histidine-Tagged Proteins

A new chromogenic chemosensor based on lysine-functionalized silver nanoparticles 1 was prepared and characterized by transmission electron microscopy (TEM), Fourier transform Raman, and ultraviolet-visible (UV-vis) spectroscopy. The color changes of nanoparticles 1 in the absence and the presence of metal ion were observed upon addition of various amino acids and proteins in aqueous solution. Among the various amino acids, the sensor 1 in the absence of metal ion shows a novel colorimetric sensor with capability to probe histidine and histidine-tagged proteins. On the other hand, the color changes of 1 in the presence of metal ions such as KCl or NiCl(2) did not occur with any amino acids. Therefore, the sensor 1 in the absence of metal ion responds selectively to histidine, a response which can be attributed to its aggregation induced by histidine with high numbers of electrostatic interactions. This highly selective sensor 1 allows a rapid quantitative assay of histidine to concentrations as low as 5.0 microM, providing a new tool for the direct measurement of histidine and histidine-tagged proteins in vitro system. Furthermore, we examined the effect of pH on absorbance (A(520)) of 1 in the presence of histidine (pH 4-12). The absorbance under basic conditions was higher than that under acidic or neutral conditions, in accord with the stronger aggregation of 1 with histidine by electrostatic interaction between the carboxylate anion of 1 and ammonium protons of histidine under basic conditions.

Fluorescent Composite Hydrogels of Metal–Organic Frameworks and Functionalized Graphene Oxide

GO MOFs! Azobenzoic acid functionalized graphene (A-GO) can act as a structure-directing template that influences hydrogel formation together with metal-organic frameworks (MOFs). Zn(2+) MOFs of pyridine derivatives work as framework linkers between the A-GO sheets (MOF-A-GO, see figure). MOF-A-GO exhibits a strong fluorescence enhancement upon gel formation. In addition, MOF-A-GO selectively recognizes trinitrotoluene.

A tetrazole-based metallogel induced with Ag+ ion and its silver nanoparticle in catalysis

A tetrazole-based ligand forms a supramolecular metallogel in the presence of Ag+ in aqueous solution at basic condition. The silver-induced metallogel has been characterized by SEM, TEM, XRD and rheometry. The metallogel exhibits a fiber structure. Upon standing, silver nanoparticles grow in the gel. TEM confirmed that the particles are exclusively formed in the gel fibers. The size of the silver nanoparticles formed on the gel fibers is dependent to the concentration of silver during gel formation. The silver nanoparticles show a face-centered cubic crystalline structure. The silver nanoparticles can effectively catalyze reduction of 4-nitrophenol by sodium borohydride in aqueous solution. The formation of Ag+-induced metallogels does not strongly depend on anions. According to DFT calculations, two silver cations are coordinated to nitrogen at the tetrazole moiety. The other silver cation is coordinated to the nitrogen of the pyridine and coordinated to the oxygen of the amide moiety. Furthermore, the rheological properties of the Ag+-tetrazole-based metallogel were strongly dependent on the concentration of AgClO4.

tert-Butylated spirofluorene derivatives with arylamine groups for highly efficient blue organic light emitting diodes

A series of tert-butylated spirofluorene derivatives incorporating a diphenylaminoaryl-vinyl group was synthesized via the Horner–Wadsworth–Emmons olefination and a Suzuki cross-coupling reaction. To examine the electroluminescent properties of these materials, multilayered OLEDs were fabricated into the following device structure: ITO/DNTPD/NPB/MADN:blue dopant materials 1–14/Alq3/Liq/Al. All devices showed efficient blue emission. In particular, one device exhibited highly efficient sky blue emission with a maximum luminance of 25 100 cd m−2 at 8.5 V, as well as luminous, power and external quantum efficiencies of 9.5 cd A−1, 5.1 lm W−1 and 6.7% at 20 mA cm−2, respectively. The peak wavelength of electroluminescence was 458 and 484 nm with CIEx,y coordinates of (0.14, 0.21) at 8.0 V. In addition, a deep blue device with CIEx,y coordinates of (0.15, 0.15) at 8.0 V showed a luminous efficiency and external quantum efficiency of 3.8 cd A−1 and 3.3% at 20 mA cm−2, respectively.

Instant visual detection of picogram levels of trinitrotoluene by using luminescent metal-organic framework gel-coated filter paper.

There is an ongoing need for explosive detection strategies to uncover threats to human security including illegal transport and terrorist activities. The widespread military use of the explosive trinitrotoluene (TNT) for landmines poses another particular threat to human health in the form of contamination of the surrounding environment and groundwater. The detection of explosives, particularly at low picogram levels, by using a molecular sensor is seen as an important challenge. Herein, we report on the use of a fluorescent metal-organic framework hydrogel that exhibits a higher detection capability for TNT in the gel state compared with that in the solution state. A portable sensor prepared from filter paper coated by the hydrogel was able to detect TNT at the picogram level with a detection limit of 1.82 ppt (parts per trillon). Our results present a simple and new means to provide selective detection of TNT on a surface or in aqueous solution, as afforded by the unique molecular packing through the metal-organic framework structure in the gel formation and the associated photophysical properties. Furthermore, the rheological properties of the MOF-based gel were similar to those of a typical hydrogel.

Coordination polymer gel derived from a tetrazole ligand and Zn2+: spectroscopic and mechanical properties of an amorphous coordination polymer gel

A tetrazole-based ligand forms a supramolecular gel in the presence of transition metal ions, particularly Zn2+, Cu2+ and Co2+. The gels have been characterized by SEM, TEM, fluorescence spectroscopy, rheometry and fluorescence microscopy. The polymer exhibits a strong fluorescence enhancement upon gel formation. According to DFT calculations, one of Zn2+ is bound to 4 tetrazole moieties and 2 solvent molecules by octahedral structure. The Zn2+-induced gelation does not strongly depend on anions. The Zn2+-tetrazole ligand gel shows a spherical structure with 20–50 nm diameter. The rheological properties of the Zn2+-tetrazole ligand gel were strongly dependent on the concentration of Zn2+.

Fluorescence enhancement of a tetrazole-based pyridine coordination polymer hydrogel

Hydrogelation of a pyridine derivative (1) possessing tetrazole moieties as end groups, without long alkyl chain groups, results in the formation of a Mg(NO3)2 coordination polymer gel. The polymer exhibits a strong fluorescence enhancement upon gel formation. 1 can also be gelated with a variety of magnesium anions such as SO42−, NO3−, Cl−, Br− and I−, indicating that the coordination polymer gel formation of 1 does not strongly depend on anions. The SEM and AFM images of Mg2+ coordination polymer gel 1 display a fibrillar network several micrometres long, with widths in the range of 60–70 nm and thicknesses of about 3 nm. In addition, photophysical studies show that the hydrogel exhibits a typical π–π* transition and gives rise to high fluorescence behavior. The coordination polymer hydrogel exhibits viscoelastic behavior as evidenced from the rheological studies.

Facile synthesis and characterization of iridium(III) complexes containing an N-ethylcarbazole–thiazole main ligand using a tandem reaction for solution processed phosphorescent organic light-emitting diodes

A new series of highly efficient phosphorescent Ir(III) complexes, which have potential applications in solution processable phosphorescent organic light-emitting diodes (PhOLEDs), were synthesized and their photophysical, electrochemical, and electroluminescent (EL) properties were investigated. The Ir(III) complexes, including (Et-Cz–Tz)2Ir(pic), (Et-Cz–Tz)2Ir(pic-N-O), (Et-Cz–Tz)2Ir(EO2–pic), and (Et-Cz–Tz)2Ir(EO2–pic-N-O), are comprised of linked N-ethylcarbazole (Et-Cz) and thiazole (Tz) units as the main ligand (Et-Cz–Tz) and picolinic acid (pic) and picolinic acid N-oxide (pic-N-O) as ancillary ligands. In addition, some of the Ir(III) complexes contain an ethylene oxide solubilizing group attached to the ancillary ligands via a tandem reaction. High performance, solution processable PhOLEDs, fabricated using (Et-Cz–Tz)2Ir(EO2–pic), were observed to have a maximum external quantum efficiency of 6.08% and a luminance efficiency of 10.98 cd A−1. This is the first report on the use of EO2–pic and EO2–pic-N-O ancillary ligands for the synthesis of solution processable Ir(III) complexes via a tandem reaction. The performances of the PhOLEDs based on these Ir(III) complexes correlate well with the theoretical properties predicted by using density functional theory calculations.