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/H₂O, 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/–NH₂ functions. The kinetic and optical behavior of the probe suggested that interaction occurred in two steps with Cu²⁺ (complexation and hydrolysis; ^absk_1,2,3(Cu²⁺₎ = 1.17, 0.74 and 0.06 s⁻¹) and ClO⁻ (hydrolysis and deprotonation; ^absk_1,2(ClO−₎ = 3.0 and 0.60 s−¹) ions while CN⁻ (^absk_1,2(CN−₎ = 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_Cu²⁺ = 3.23 × 10⁶ M⁻¹; LOD, 18.5; K_ClO⁻ = 5.23 × 10⁵ M⁻¹ and LOD, 23.2; K_CN⁻ = 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.