Unveiling the highly selective time-dependent colorimetric response of 8-hydroxyquinoline and indolinium-conjugated donor-π-acceptor (D-π-A) hybrid for the detection of copper(II) ions

Abstract

A novel indolinium-8-hydroxyquinoline-based donor-π-acceptor colorimetric chemosensor, IQS, was synthesized and systematically investigated time-dependent colorimetric response for the selective detection of Cu 2+ ions. The probe exhibited a distinct, time-dependent color changes with copper(II) ions in a DMSO-H2O (8:2, v/v) medium, enabling visual detection. UV-visible absorption studies revealed pronounced bathochromic shifts and the formation of new absorption bands upon Cu 2+ coordination. Further, Job's plot analysis confirmed a 2:1 (IQS: Cu 2+ ) binding stoichiometry. The probe displayed excellent selectivity with negligible interference from other metal ions. The limit of detection for Cu 2+ was 3.98 x 10 -5 M within 5 min and enhanced to 1.31 x 10 -5 M after 24 h. Binding constant values 2.40 x 10 2 M -2 (within 5 minutes) and 2.73 x 10 2 M -2 (after 24 h), indicating strong affinity toward Cu 2+ ions. Density functional theory (DFT) and TD-DFT analyses demonstrated a decrease of the HOMO-LUMO energy gap and enhanced charge-transfer character upon complexation. These results confirm that IQS is a robust colorimetric chemosensor, facilitating the selective and timedependent detection of Cu 2+ .