The increase in the absorption intensity at 460 nm attained saturation at the concentration at 50 μM of Cu 2+ (Figure ) and the ratiometric point graph plotted between the absorption intensities (A460 nm/A536 nm) and concentration of Cu 2+ (μM) demonstrated the initiation of sensing response towards the Cu 2+ started even below 1 μM of concentration (Figure ). PTE-EA also displayed colorimetric response as changing the color of solution from purple to yellowish green after Cu 2+ complexation visible to naked eyes in the daylight (Figure , inset). The ratiometric graph plotted between A460/A536 nm v/s concentrations of Cu 2+ [M], presented two steps of linear change between two concentrations of Cu 2+ ranging from 0-20 μM and 20-50 μM and resulted in very good correlations having R 2 values 0.993 and 0.995, respectively (Figure S1, ESI). This resulted in nano molar detection limits for both concentrations of Cu 2+ and found to be 17.9 nM (0-20 μM) and 3 nM (20-50 μM).