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

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journal contribution
posted on 23.03.2016, 11:49 by K. S. Bejoymohandas, Ajay Kumar, S. Sreenadh, E. Varathan, S. Varughese, V. Subramanian, M. L. P. Reddy
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 × 102-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 1H 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.

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