An Azo Dye Based D-pi-A Chromogenic Probe for Selective Naked-Eye Detection of Hg2+ Ion: Application in Logic Gate Operation

摘要

The current work describes the selective colorimetric detection of metal ions using a simple azo dye (L1) containing donor-pi-acceptor framework. In this chromogenic probe, salicylaldehyde is used as donor and nitrobenzene group as acceptor unit. L1 is found to show selective recognition of mercuric ion both visually and spectrophotometrically with no interference from environmentally relevant metal ions in DMSO-water mixture. It exhibits reddish-pink colour in DMSO-water medium as a result of intramolecular charge transfer (ICT) from the electron donating phenolic group to electron withdrawing nitrobenzene group. It selectively binds with Hg2+ even in presence of other interfering metal ions and form a 1 : 1 L1-Hg2+ adduct. It is evident from a change in colour along with a decrease of ICT absorption band and hypsochromic shift of pi-pi* band. The binding of the chemosensor and mercuric ion through the salicylaldehyde unit is proved from H-1-NMR data and DFT calculations. Using UV-Vis spectroscopic technique the detection limit and binding constant values are calculated to be 6 mu M and 3.3 x 10(3) M-1 respectively. Hg2+ probing process displays reversibility upon addition of fluoride ion. The on-off-on colorimetric change on sequential addition of Hg2+ and F- mimics an IMPLICATION type logic gate.