Colorimetric and fluorometric dual sensing of trace water in methanol based on a Schiff Base-Al3+ ensemble probe.

A new julolidine based Schiff base receptor (L) was synthesized and characterized. L forms a 1:1 complex with Al3+ in methanol, resulting in an immediate color change from chartreuse to orange and a remarkable enhancement in its emission intensity along with a bathochromic shift from 540 nm to 570 nm. Addition of trace amounts of water significantly quenches the fluorescence emission, where a decomplexation of Al3+ from the L-Al3+ complex takes place. The significant quenching effect indicated that the L-Al3+ ensemble system can be used to detect trace water in commercial methanol. From the fluorescence titration, the detection limit for sensing water in methanol was estimated to be 0.0047%. We have also made an easy-to-prepare test strip of L-Al3+ to detect water in methanol through naked-eye observation, which is possible to realize in situ monitoring.