A fluorescent turn-on probe for Hg2+ with a high contrast designed by manipulating functional groups tethered to naphthalimide

[Display omitted] •Naphthalimide-based Hg2+ fluorescent turn-on probe 1 have been developed.•Probe 1 was designed by modification of the previously reported Cd2+ probe.•A quite low background signal, and high sensitivity for Hg2+.•High selectivity and a low detection limit (2.8 nM).•Probe 1 could be useful for quantitative analysis for Hg2+ in tap and river water. Based on the concept provided by our previous work on a fluorescent Cd2+ probe, a fluorescent turn-on Hg2+ probe with a high contrast was designed through manipulating functional groups tethered to naphthalimide. With carbamoylmethylamino and bis[2-(ethylthio)ethyl]amino groups as tethering functionalities, 1 worked as a useful fluorescent probe in a high selective and sensitive manner over the pH range between 6 and 8 with a detection limit at 2.8 nM (estimated at a pH of 7.2). Comparison of the probe performance of 1 with that of 2 merely with bis[2-(ethylthio)ethyl]amino group suggested that both of the tethering groups exhibited their abilities to chelate with Hg2+, and yet the carbamoylmethylamino group also functioned as a fluorescent off-on switch through a photoinduced electron transfer mechanism. Thus, 1 found a practical utility as an Hg2+ probe in analysis of river as well as tap samples without any tedious pretreatments.