Naphthalimide-Rhodamine based chemosensors for colorimetric and fluorescent sensing Hg2+ through different signaling mechanisms in corresponding solvent systems

A couple of 1,8-naphthalimide-Rhodamine based chemosensors R6G-NA and RB-NA are successfully designed and synthesized with high selectivity and sensitivity to Hg2+. R6G-NA exhibits typical fluorescence resonance energy transfer (i.e. FRET) signal from 1,8-naphthalimide to Rhodamine 6G along with an obvious color change from yellow to orange when interacting with Hg2+ in pure CH3CN. While RB-NA in CH3CN/HEPES buffer (1:1, v/v) can only act a photo-induced electron transfer off (i.e. PET-OFF) process in 1,8-naphthalimide with the fluorescence intensity centered at 525 nm increasing after adding Hg2+. However, in pure CH3CN system, the spirolactam ring of Rhodamine B in RB-NA can be opened by the Hg2+ along with the block of PET process in 1,8-naphthalimide which leads to a new emission band emerging at 575 nm and the intensity of fluorescence enhancement at 515 nm together with the color clearly changing from yellow to pink. (C) 2015 Elsevier B.V. All rights reserved.