Naphthalimide-Piperazine Derivatives as Multifunctional "On" and "Off" Fluorescent Switches for pH, Hg 2+ and Cu 2+ Ions

• Published in: Molecules (Basel, Switzerland) Vol. 28; no. 3
• Main Authors: Pršir, Kristina, Matić, Mislav, Grbić, Marlena, Mohr, Gerhard J, Krištafor, Svjetlana, Steinberg, Ivana Murković
• Format: Journal Article
• Language: English
• Published: Switzerland 28.01.2023
• Subjects: chemosensors; heavy metals; pH; fluorescent switch; metal ion; 1,8-naphthalimide
• ISSN: 1420-3049

Novel 1,8-naphthalimide-based fluorescent probes and were designed and screened for use as chemosensors for detection of heavy metal ions. Two moieties, methylpyridine ( ) and hydroxyphenyl ( ), were attached via piperazine at the C-4 position of the napthalimide core resulting in a notable effect on their spectroscopic properties. and are pH sensitive and show an increase in fluorescence intensity at around 525 nm (switch "on") in the acidic environment, with p values at 4.98 and 2.91, respectively. Amongst heavy metal ions only Cu and Hg had a significant effect on the spectroscopic properties. The fluorescence of is quenched in the presence of either Cu or Hg which is attributed to the formation of 1:1 metal-ligand complexes with binding constants of 3.6 × 10 and 3.9 × 10 , respectively. The chemosensor can be used for the quantification of Cu ions in sub-micromolar quantities, with a linear range from 250 nM to 4.0 μM and a detection limit of 1.5 × 10 M. The linear range for the determination of Hg is from 2 μM to 10 μM, with a detection limit of 8.8 × 10 M. Conversely, behaves like a typical photoinduced electron transfer (PET) sensor for Hg ions. Here, the formation of a complex with Hg (binding constant 8.3 × 10 ) turns the green fluorescence of into the "on" state. showed remarkable selectivity towards Hg ions, allowing for determination of Hg concentration over a linear range of 1.3 μM to 25 μM and a limit of detection of 4.1 × 10 M.