An Azo Dye Based D-π-A Chromogenic Probe for Selective Naked-Eye Detection of Hg~(2+) Ion: Application in Logic Gate Operation

摘要

The current work describes the selective colorimetric detection of metal ions using a simple azo dye (L~(-1)) containing donor-π-acceptor framework. In this chromogenic probe, salicylalde-hyde is used as donor and nitrobenzene group as acceptor unit. L~(-1) 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 Hg~(2+) even in presence of other interfering metal ions and form a 1:1 L~(-1)-Hg~(2+) adduct. It is evident from a change in colour along with a decrease of ICT absorption band and hypsochromic shift of π-π~* band. The binding of the chemosensor and mercuric ion through the salicylaldehyde unit is proved from 1H-NMR data and DFT calculations. Using UV-Vis spectroscopic technique the detection limit and binding constant values are calculated to be 6 μM and 3.3 x 10~3 M~(-1) respectively. Hg~(2+) probing process displays reversibility upon addition of fluoride ion. The on-off-on colorimetric change on sequential addition of Hg~(2+) and F mimics an IMPLICATION type logic gate.