Aggregation-induced Emission Active Naphthalimide Derived Schiff Base for Detecting Cu²⁺ and Its Applications

Area of Science:

• Materials Science
• Organic Chemistry
• Analytical Chemistry

Background:

• Aggregation-induced emission (AIE) is a photophysical phenomenon where molecules are non-emissive in solution but become highly fluorescent upon aggregation.
• Schiff bases are versatile organic compounds with wide applications, including sensing and optoelectronics.
• Developing novel AIE luminogens for selective ion detection remains a significant challenge in analytical chemistry.

Purpose of the Study:

• To synthesize and characterize a novel aggregation-induced emission (AIE) active Schiff base (NHS).
• To investigate the photophysical properties of NHS, particularly its fluorescence behavior in response to environmental changes and metal ion addition.
• To evaluate the potential of NHS as a selective sensor for copper ions (Cu2+) in aqueous samples.

Main Methods:

• Synthesis of Schiff base (NHS) via condensation of naphthalimide hydrazide and salicylaldehyde.
• Characterization of AIE properties using UV-Vis absorption and fluorescence spectroscopy.
• Investigation of aggregation behavior using Dynamic Light Scattering (DLS).
• Metal ion sensing studies with various cations and analysis of selectivity.
• Density Functional Theory (DFT) and Stern-Volmer analysis for mechanistic insights.
• Application in real water sample analysis for quantitative and qualitative Cu2+ detection.

Main Results:

• The synthesized Schiff base (NHS) exhibited AIE properties, transitioning from non-fluorescent in DMSO to emissive in DMSO:HEPES mixtures (70-95% HEPES).
• NHS demonstrated a selective fluorescence 'switch-off' response specifically for Cu2+ ions, attributed to the chelation-enhanced quenching (CHEQ) effect.
• The sensing mechanism was further elucidated through DFT calculations and Stern-Volmer analysis.
• The practical utility of NHS was successfully demonstrated through the quantitative and qualitative analysis of Cu2+ in real water samples.

Conclusions:

• A novel AIE-active Schiff base (NHS) was successfully synthesized and characterized.
• NHS shows potential as a selective and sensitive fluorescent probe for Cu2+ detection in aqueous environments.
• The developed sensor offers a promising tool for environmental monitoring and water quality assessment.