A Categorical Naked‐Eye Detection of Cu²⁺ and Zn²⁺ through a Donor‐Acceptor‐Donor (D‐A‐D)‐Type Salicylaldimine: An Experimental and Theoretical Approach

Abstract

A Schiff base viz., 2,3‐bis‐(3, 5‐di‐tert‐butyl‐2‐hydroxybenzylidene) amino maleonitrile (TBCN), having donor–acceptor–donor (D–A–D) type constitution exhibited Cu2+ and Zn2+ guided specific modulations in its ICT (intramolecular charge transfer) characteristics. The corresponding naked eye changes for Cu2+ and Zn2+ involved the shifting of characteristic ICT band of TBCN at ∼472 nm (yellow) to ∼ 566 nm (pink) and ∼590 nm (indigo blue) respectively in a semi‐aqueous medium (EtOH:H2O in a ratio of 8:2 v/v). The TBCN as well as its ensembles with Cu2+ and Zn2+ were fully characterized through their single crystal XRD studies along with spectroscopic and mass spectral studies. The DFT and the time‐dependent DFT calculations provided a genuine rationale for separate naked eye colorimetric changes of TBCN for Cu2+ and Zn2+.