As an electron donor, it efficiently performs the intramolecular charge transfer ICT and acceptor excited a-PET to the electron deficient perylene core before binding to the Cu 2+ , thus PTE-EA demonstrated strong bathochromic ICT absorption band at 536 nm and feeble fluorescence intensity at 520 nm, respectively in HEPE buffer-CH3CN (3:7, v/v, pH 7.3). Accordingly, the complexation of PTE-EA with Cu 2+ , result in blue shift (Δλ = 76 nm) of the absorption maxima with new hyperchromic absorption band at 460 nm, owing to suppression of ICT mechanism and visual color change of solution from purple to yellowish green as colorimetric response.