Dual optical properties of new schiff base based on bisthiophene for sensing of Cu2+ in protic media

Abstract

In this paper, a new dual optical behavior Cu2+ selective Schiff base (L) was developed by reacting thiophene carbaldehyde with diamino malononitrile. The sensing ability of L was studied with different metal ions by visual test, UV–Vis and spectrofluorometric methods in MeOH:H2O (8:2, v/v) media. Accordingly, the visual test was confirmed by changing initial yellow to colorless upon interaction with Cu2+ while for other it did not respond in natural light while the same solution when it observed under UV light, it exhibits emission color (cyan) only with Cu2+. Spectrophotometrically, L alone exhibits a strong absorption band at 420 nm, upon interaction with Cu2+, it exhibits an additional new peak at 290 nm while spectrofluorimetrically, a new emission peak was observed at 360 nm while other metal ions it does not exhibits this optical behavior. The spectral titration data reveals that the LOD limit down to of 6.21 × 10−6 and 1.45 × 10−8 M by UV–vis and fluorescence respectively which is lower than the WHO guidelines (0.02 μM) in drinking water. The formation 1:1 binding stoichiometry of host-guest complexation between L and Cu2+ is studied by using Jobs plot and the binding capacity is estimated by Benesi-Hilderbrand method (Ka = 7.31 × 104 M-1). The coordination behavior of L with Cu2+ is well supported by FTIR, 1H NMR, 13C NMR, ESI mass spectral data and theoretical calculations using Gaussian 09 W program.