A fluorescent and colorimetric probe for sensing trace water in ethanol and methanol based on an Al (III) complex of rhodamine-B Schiff base

A novel fluorescent and colorimetric probe was synthesized by the complexation of rhodamine-B Schiff base (L) and Al3+, which could be used to quickly detect trace water in ethanol and methanol. L showed a remarkable fluorescence enhancement and colorimetric responses upon reaction with Al3+. However, the intensity was significantly quenched upon the addition of trace water to the L-Al3+ solution, and the degree of quenching (1-I/I0) reached 94 % in ethanol and 88 % in methanol. Meanwhile, a significant change in color was also observed by the naked-eye from pink to colorless in the L-Al3+ solution. The fluorescent and colorimetric changes indicated that water could induce the dissociation of the L-Al3+ complex. Moreover, the L-Al3+ complex exhibited a good anti-interference fluorescence response to trace water in ethanol and methanol compared with other solvents. Also, the limit of detection (LOD) for ethanol and methanol were calculated as 0.0053 % v/v and 0.0080 % v/v respectively based on 3.3δ/k. Furthermore, the sensing mechanism of the L-Al3+ complex toward trace water was investigated by 1H NMR, HR-MS, FTIR, pH and AIE. Additionally, the L-Al3+ complex showed potential application in the detection of trace water in real ethanol methanol.