A Highly Selective Chemosensor for Cyanide Derived from a Formyl-Functionalized Phosphorescent Iridium(III) Complex

Abstract

A new phosphorescent iridium(III) complex, bis[2',6'-difluorophenyl-4-formylpyridinato-N,C4']iridium(III) (picolinate) (IrC), was synthesized, fully characterized by various spectroscopic techniques, and utilized for the detection of CN(-) on the basis of the widely known hypothesis of the formation of cyanohydrins. The solid-state structure of the developed IrC was authenticated by single-crystal X-ray diffraction. Notably, the iridium(III) complex exhibits intense red phosphorescence in the solid state at 298 K (ΦPL = 0.16) and faint emission in acetonitrile solution (ΦPL = 0.02). The cyanide anion binding properties with IrC in pure and aqueous acetonitrile solutions were systematically investigated using two different channels: i.e., by means of UV-vis absorption and photoluminescence. The addition of 2.0 equiv of cyanide to a solution of the iridium(III) complex in acetonitrile (c = 20 μM) visibly changes the color from orange to yellow. On the other hand, the PL intensity of IrC at 480 nm was dramatically enhanced ∼5.36 × 10(2)-fold within 100 s along with a strong signature of a blue shift of the emission by ∼155 nm with a detection limit of 2.16 × 10(-8) M. The cyanohydrin formation mechanism is further supported by results of a (1)H NMR titration of IrC with CN(-). As an integral part of this work, phosphorescent test strips have been constructed by impregnating Whatman filter paper with IrC for the trace detection of CN(-) in the contact mode, exhibiting a detection limit at the nanogram level (∼265 ng/mL). Finally, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to understand the electronic structure and the corresponding transitions involved in the designed phosphorescent iridium(III) complex probe and its cyanide adduct.

Luminescent chemosensors by using cyclometalated iridium(iii) complexes and their applications

“…An exception to this is the reaction-based chemosensor for cyanide ions reported by Reddy and co-workers, which relied on the specific cyanohydrin reaction between an aldehyde group attached to the C^N ligand and the target ion in order to generate selectivity. 57 The complex therefore showed very little response even to 10-fold excess of unrelated anions, and additionally, could offer a ratiometric mode of detection due to the change in emission wavelength of the complex upon cyanohydrin formation. In general, ratiometric or switch-on modes of detection are preferable to a switch-off detection method as these are less susceptible to false positives arising due to non-specific quenching species in the sample matrix.…”

“…6a), for the detection of CN – on the basis of the widely known cyanohydrin forming reaction. 57 The room-temperature emission profile of 6 is featureless and broad with a full-width at half-maximum value of about 166 nm, which indicates the dominance of a 3 MLCT excited-state emission rather than a LC 3 π–π* excited-state emission. Complex 6 alone in acetonitrile exhibits a rather weak and broad emission profile with an emission maximum at 635 nm.…”

A Turn‐On Fluorescence Chemosensor for Cyanide in Aqueous Media Based on a Nucleophilic Addition Reaction

“…The sensing abilities of CX towards various anions (CN  , F  , Cl  , Br  , I  , AcO  , 2 4 H PO -, 4 HSO -, 4 ClO -, SCN  , S 2 , 3 4 PO -, and To further explore the utility of sensor CX as an ion-selective chemosensor for CN − , competitive experiments were carried out in the presence of 50 equiv. of CN  and 50 equiv.…”

“…Tetrabutylammonium salt of anions (F  , Cl  , Br  , I  , AcO  , 2 4 H PO -, 4 HSO -, 4 ClO -, SCN  , S 2 , 3 4 PO -, 2 3 COand CN  ) were used for the fluorescence experiments. Any changes in the fluorescence spectra of the synthesized compound were recorded on addition of tetrabutylammonium salts while keeping the ligand concentration constant (2.0×10 5 mol•L 1 ) in all experiments.…”

“…[1][2][3][4][5][6][7] Many efforts have been made to design chemosensors for anions such as F  , CN  , Cl  , 2 4 H PO -, 4 SO -, AcO  , etc. [1][2][3][4][5][6][7] Many efforts have been made to design chemosensors for anions such as F  , CN  , Cl  , 2 4 H PO -, 4 SO -, AcO  , etc.…”