A structurally characterized novel dual–pocketed tetra–conjugated bisphenol–based chromophore (fluorescence = 652 nm) was synthesized in gram scale in ∼90% yield from its tetraaldehyde. Highly selective, naked-eye detection of CN– (DMSO/H2O) and was confirmed by interferent testing. A detection limit of 0.38 µM, within the permissible limit of CN– concentration in drinking water as mandated by WHO. The “reversibility” study shows potential applicability and reusability of Sen. Moreover, cost-effective and on-site interfaces, application tools such as fabricated cotton swabs, plastic Petri dishes, and filter papers further demonstrated the specific selectivity of Sen for the toxic CN–. In addition, an easily available and handy smartphone-assisted “Color Picker” app was utilized to help estimate the concentration of CN– ion present. Dual phenol deprotonation mechanism is active and supported by 1H NMR spectroscopic data and DFT calculation results.