A novel fluorogenic hybrid material for selective sensing of thiophenols

A fluorogenic organic-inorganic hybrid sensory material (denoted as material III) was successfully prepared by immobilizing disulfide-based receptors within the channels of mesoporous silica MCM-41. The material showed high sensitivity and excellent selectivity towards thiophenols due to appropriate combination of the stronger nucleophilicity of thiophenols and the secondary interactions (hydrophobicity and pi-pi stacking interactions) provided by the inorganic support. Fluorescence measurements revealed that the emission intensity of material III increased significantly upon addition of thiophenols, while it was not observed for aliphatic thiols and other nucleophiles. The detection limit of this material to p-toluenethiol was estimated to be 7.4 x 10(-6) M, and a good linear relationship between the fluorescence intensity and p-toluenethiol concentration (in the range of 0-110 mu M) was achieved. The pronounced emission enhancement could be attributed to the following conversion process: a coumarin derivative is released from material III by cleaving the disulfide bonds in the presence of thiophenols, and then oxidized spontaneously to a fluorescent dye (coumarin 6) under ambient conditions. This novel sensing method via disulfide-based groups as the active site combining with the synergistic effect provided by the inorganic support is expected to open a new avenue for thiophenols sensing.