A lanthanide doped metal-organic framework demonstrated as naked eye detector of a trace of water in organic solvents including alcohols by monitoring the turn-on of luminescence

Abstract

It is very crucial to have a very simple, instant and low-cost detection and estimation of a trace of water in common organic solvents including alcohols. To obtain the sensor material we have synthesized a metal-organic framework (MOF) {[Y1.0Mn1.5(PDA)3(H2O)3]·3.5H2O}, 1, (PDA = 2,6-pyridinedicarboxylic acid) through hydrothermal process. A doping of compound 1 by 10 % terbium {[Y0.9Tb0.1Mn1.5(PDA)3(H2O)3]·3.5H2O}, 1:Tb, was done through an isomorphous substitution technique. The most advantageous point about 1:Tb was the metal centre luminescence, which was largely stokes shifted from the excitation light making possible the naked eye observation. The weak metal centre luminescence intensity of dehydrated 1:Tb (excluding lattice and coordinated water molecules) in organic solvents EtOH, CH3OH, CH3CN, THF and n-heptane showed huge turn-on in presence of trace amounts of H2O in the said solvents. The luminescence intensity of Tb3+ centre was enhanced by several folds with a limit of detection 1.12 %(v/v), 0.47 %(v/v), 0.04 %(v/v), 0.13 %(v/v) and 0.53 %(v/v) respectively. The coordinated water molecules as well as the lattice water molecules in 1:Tb play a vital role during sensitization of the Tb3+ centre by enhancing the rigidity of the structure and facilitating the formation of LMCT state which ultimately results in a huge turn-on of metal centre luminescence.