A Categorical Naked‐Eye Detection of Cu 2+ and Zn 2+ through a Donor‐Acceptor‐Donor (D‐A‐D)‐Type Salicylaldimine: An Experimental and Theoretical Approach

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 Cu 2+ and Zn 2+ guided specific modulations in its ICT (intramolecular charge transfer) characteristics. The corresponding naked eye changes for Cu 2+ and Zn 2+ 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:H 2 O in a ratio of 8:2 v/v). The TBCN as well as its ensembles with Cu 2+ and Zn 2+ 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 Cu 2+ and Zn 2+ .