From Acidochromism to Device Fabrication: A DFT-Backed Chemosensor for Portable Co²⁺ and Cu²⁺ Sensing

For the purpose of selectively detecting Co²⁺ and Cu²⁺ ions using a combination of colorimetric and fluorometric responses, a novel coumarin-imidazole-thiazole based chemosensor 6-chloro-3-(2-(2-(4-(diphenylamino)phenyl)-1H-phenanthro[9,10-d]imidazol-1-yl)thiazol-4-yl)-2H-chromen-2-one (TDC2) was created and thoroughly studied. When TDC2 interacts with Co²⁺ and Cu²⁺, it shows noticeable colour changes, the colour changes from mild yellow to sea blue for Cu²⁺ and in presence of Co²⁺ ions colour changes to baby pink along with strong fluorescence quenching, but it is insensitive to other competing metal ions. Excellent linearity and high sensitivity are demonstrated by UV-visible and fluorescence titration tests, with nanomolar limits of detection of 45 nM for Co²⁺ and 68 nM for Cu²⁺. The sensor exhibits reversible acidochromic behaviour toward volatile acid vapours and functions well across a broad pH range. Polymer-embedded films and paper-strip devices were developed to convert molecular sensing into useful platforms. These allowed for quick, portable, on-site detection with distinct visual responses under both visible and UV light. TDC2 is positioned as a reliable and application-focused sensor for real-time monitoring of Co²⁺ and Cu²⁺ ions due to its combination solution-state performance, solid-state device integration, and theoretical validation.