Naphthalimide modified rhodamine derivative: ratiometric and selective fluorescent sensor for Cu2+ based on two different approaches.

A new rhodamine-based derivative bearing a 1,8-naphthalimide group (1) was synthesized as a dual-mode Cu(2+)-selective sensor via the rhodamine ring-opening approach and ratiometric displacement. A colorimetric and "off-on" signal for Cu(2+) through rhodamine ring opening in 1 and ratiometric fluorescent signal output when Cu(2+) displaces the bound Zn(2+) in the 1-Zn(2+) complex can be observed.