Abstract

We report the synthesis and theoretical study of two new colorimetric chemosensors with special selectivity and sensitivity to Ni2+ and Cu2+ ions over other metal cations in the CH3CN/H2O solution. Compounds (E)-4((2-nitrophenyl)diazenyl)-N,N-bis(pyridin-2-ylmethy)aniline (A) and (E)-4((3-nitrophenyl)diazenyl)-N,N-bis-(pyridin-2-ylmethyl)aniline (B) exhibited a drastic color change from yellow to colorless, which allows the detection of the mentioned metal cations through different techniques. The interaction of sensors with these metal ions induced a new absorption band with a hypsochromic shift to the characteristic signal of the free sensors. A theoretical study via time-dependent density functional theory (TD-DFT) was performed. This method has enabled us to reproduce the hypsochromic shift in the maximum UV-vis absorption band and explain the selective sensing of the ions. For all of the systems studied, the absorption band is characterized by a pi -> pi* transition centered in the ligand. Instead of Ni2+ and Cu2+ ions, the transition is set toward the 0* molecular orbital with a strong contribution of the 3d (2)(x)-(2)(y) transition (pi -> 3d(x)(2)-(2)(y)). These absorptions imply a ligand-to-metal charge transfer (LMCT) mechanism that results in the hypsochromic shift in the absorption band of these systems.