Kyo Han Ahn

Selective Fluorogenic and Chromogenic Probe for Detection of Silver Ions and Silver Nanoparticles in Aqueous Media

A novel rhodamine-based fluorogenic and chromogenic probe for Ag(+) ions in aqueous media is developed, which can be also used for the detection of AgNPs. The sensing mechanism is based on irreversible tandem ring-opening and -forming processes promoted by Ag(+)-coordination to the iodide of the probe, which is accompanied by both color and turn-on type fluorescence changes. The probe shows remarkably high selectivity over other metal ions and detects silver ions up to 14 ppb.

Fluorescence modulation in anion sensing by introducing intramolecular H-bonding interactions in host–guest adducts

Fluorescence signaling in anion binding is modulated from quenching to enhancement by intramolecular H-bonding stabilization of anion-ionophore adducts; the intramolecular H-bonding is suggested to suppress the quenching processes otherwise possible and increase the conformational rigidity of the anionic adducts, leading to fluorescence enhancement in a selective fashion towards cyanide ion, among the various anions examined.

A “Reactive” Ratiometric Fluorescent Probe for Mercury Species

A ratiometric fluorescent probe for mercury species is developed based on the metal-promoted hydrolysis of a vinyl ether derivative of 2-(benzothiazol-2-yl)phenol in a buffer solution. The probe responds selectively to mercury species over various other metal ions with a marked fluorescence change from blue to cyan through the excited state intramolecular proton transfer (ESIPT) process. The fluorescence titration is complete with 0.5 equiv of HgCl(2), which indicates that the probe also responds to organomercury species, RHgCl.

Reaction-Based Fluorescent Sensing of Au(I)/Au(III) Species: Mechanistic Implications on Vinylgold Intermediates

A rhodamine-derived alkyne shows turn-on fluorescence change only toward Au(I)/Au(III) species among various other metal species examined. A formyloxazole compound is formed as the major product in aqueous media, presumably via a vinylgold intermediate, which casts new mechanistic implications on vinylgold intermediates.

Selective colorimetric sensing of anions in aqueous media through reversible covalent bonding.

Selective colorimetric sensing of anions in aqueous media has been studied, which involves reversible covalent bonding as key binding interactions. By introducing a simple nitro chromophore into an o-(carboxamido)trifluoroacetophenone ionophore that recognizes anions through reversible covalent bonding, we have realized a complete selectivity in colorimetric sensing of cyanide among competing anions such as fluoride, acetate, and dihydrogen phosphate in aqueous media. Such selectivity is explained by dominant reversible covalent bonding over hydrogen bonding, which leads to indirect internal charge transfer. The sensing system is readily converted into a polymeric analogue, demonstrating its potential applicability to develop a naked eye detection material for highly toxic cyanide ions.

Fluorogenic and Chromogenic Detection of Palladium Species through a Catalytic Conversion of a Rhodamine B Derivative

A simple yet efficient detection method for palladium species is developed based on a molecular sensing system that undergoes a palladium-catalyzed oxidative addition. A rhodamine B derivative thus developed undergoes the catalytic process triggered by palladium insertion and gives both turn-on fluorescence and color changes. A usefulness of the sensing system is demonstrated by determining the residual palladium contents in a purified sample prepared through a palladium-catalyzed reaction.

A Rational Approach to Fluorescence “Turn-On” Sensing of α-Amino-carboxylates

A rational approach to fluorescence turn-on sensing of amino carboxylates is described, which primarily relies on the perturbation of the quenching n−π* transition energy level of a carbonyl ionophore relative to the π−π* transition energy level of an anthracene in the sensor. The anthracene-based bis(trifluoroacetylcarboxanilide) sensor is structurally simple but selectively senses α-amino acids as their carboxylate forms over β- and γ-homologues, by forming a (1:1)-cyclic adduct with a large fluorescence enhancement factor of 110.

Highly cooperative ion-pair recognition of potassium cyanide using a heteroditopic ferrocene-based crown ether–trifluoroacetylcarboxanilide receptor

A heteroditopic receptor having crown ether and trifluoroacetylcarboxanilide groups selectively recognizes both potassium and cyanide ions in acetonitrile with an association constant of as high as Ka = 1.9 x 10(7) M(-1) through a highly cooperative ion-pair interaction, resulting in two orders of magnitude enhancement in the binding affinity.

In vivo two-photon fluorescent imaging of fluoride with a desilylation-based reactive probe

A two-photon excitable molecular probe for fluoride, developed based on a fluoride-specific desilylation reaction, is demonstrated to be useful for fluorescent imaging of fluoride ions in live zebrafish by one-photon as well as two-photon microscopy for the first time.

Dramatic Substituent Effects on the Photoluminescence of Boron Complexes of 2‐(Benzothiazol‐2‐yl)phenols

Substituents can induce dramatic changes in the photoluminescence properties of N,O-chelated boron complexes. Specifically, the boron complexes of 2-(benzothiazol-2-yl)phenols become bright deep blue- and orange-red-emitting materials depending on amino substituents at the 5- and 4-positions of 2-(benzothiazol-2-yl)phenol, respectively. Absorption and emission data show that the resulting boron complexes have little or small overlap between the absorption and emission spectra and, furthermore, X-ray crystal structures for both the blue and orange-red complexes indicate the absence of π-π stacking interaction in the crystal-packing structures. These features endow the boron complexes with bright and strong photoluminescence in the solid state, which distinguishes itself from the typical boron complexes of dipyrromethenes (BODIPYs). A preliminary study indicates that the blue complexes have promising electro-optical characteristics as dopant in an organic light-emitting diode (OLED) device and show chromaticity close to an ideal deep blue. The substituent effects on the photoluminescent properties may be used to tune the desired emission wavelength of related boron or other metal complexes.