Photochemical and electrochemical behavior of a molecular probe: Fluorescence on-off-on response to detect multiple ions (Cu2+, ClO− and CN−) with different rate of reaction

Abstract

A molecular probe 3 containing phenyl substituted imidazolyl unit and diaminomaleonitrile (DAMN) moiety has been synthesized and characterized. Photophysical and electrochemical behavior probe 3 were studied in partial aqueous medium (ACN/H<inf>2</inf>O, 9.5:0.5 v/v). Probe 3 upon interaction with different class of ions showed sensitivity for Cu2+, ClO− and CN− ions with different response time and reaction rates due to variation in intramolecular charge transfer (ICT) process. Both Cu2+ and ClO− ions displayed enhanced emission due to hydrolysis of imine bond to form compound 2 in the medium whereas, with CN− fluorescence quenching was observed due to the deprotonation of –OH/–NH<inf>2</inf> functions. The kinetic and optical behavior of the probe suggested that interaction occurred in two steps with Cu2+ (complexation and hydrolysis; absk<inf>1</inf><inf>,</inf><inf>2</inf><inf>,</inf><inf>3(Cu</inf>2+<inf>)</inf> = 1.17, 0.74 and 0.06 s−1) and ClO− (hydrolysis and deprotonation; absk<inf>1</inf><inf>,</inf><inf>2(ClO</inf>−<inf>)</inf> = 3.0 and 0.60 s−1) ions while CN− (absk<inf>1</inf><inf>,</inf><inf>2</inf><inf>(</inf><inf>CN</inf>−<inf>)</inf> = 2.13 and 1.66 s−1) induces deprotonation in one step. The interaction of probe 3 with ClO− was relatively fast than with Cu2+/CN− ions. Job's plot analysis between probe 3 and ions revealed a 1:1 (Cu2+/ClO−) and 1:2 (CN−) ratio stoichiometry with good limit of detection (nM) and binding affinity (LOD, 17; K<inf>Cu</inf>2+ = 3.23 × 106 M−1; LOD, 18.5; K<inf>ClO</inf>− = 5.23 × 105 M−1 and LOD, 23.2; K<inf>CN</inf>− = 5.50 × 109 M−2) respectively. Probe 3 displayed a naked–eye sensitive fluorescence response to detect tested ions on test paper strips and good recovery percentage of ions in real water sample analysis. © 2024 Elsevier Ltd