A New Highly Selective, Ratiometric and Colorimetric Fluorescence Sensor for Cu2+ with a Remarkable Red Shift in Absorption and Emission Spectra Based on Internal Charge Transfer

A new 1,8-diaminonaphthalene based ratiometric and highly selective colorimetric off-on type of fluorescent probe, receptor 2 has been designed and synthesized that senses only Cu2+ among the other heavy and transition metal ions examined on the basis of Internal charge transfer (ICT). The visual sensitivity of the receptor 2 Is remarkable, showing dual color changes from colorless (receptor) to purple followed by blue and a large red shift in emission upon Cu2+ complexation.