Cholesterol modified OPE functionalized film: fabrication, fluorescence behavior and sensing performance

A novel oligo(p-phenyleneethynylene) with cholesterol on its side chains (CHOL-OPE) was designed and synthesized. Film 1 and Film 2 were fabricated by immobilizing, separately, the oligomer as prepared and its control, OPE, which contains no side chains, on glass plate surfaces via utilization of a self-assembled monolayer (SAMs) technique. Fluorescence studies revealed that the profile of the fluorescence emission spectrum of Film 1 is dependent upon the composition of a mixture of THF and water. In contrast, Film 2 shows no such effect. Sensing performance studies demonstrated that the fluorescence of Film 1 is super-sensitive to the presence of 2,4,6-trinitrophenol (picric acid, PA), and sensitive to 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT) and nitrobenzene (NB) in the aqueous phase, whereas the nitroaromatics (NACs) as studied show little effect on the fluorescence emission of Film 2. The results from fluorescence quenching studies and the fact that copper salts (copper nitrate and copper acetate) show no detectible effect on the fluorescence emission of Film 1 show that the oligomer and the short linker, connecting the oligomer and the substrate, of the CHOL-OPE functionalized film may adopt a compact structure. Interestingly, the sensing process is fully reversible and free of interference from commonly found compounds, including methanol, THF, toluene, dichloromethane, ammonia, HCl, NaOH, NaCl, copper salts and seawater, etc. Fluorescence lifetime measurements revealed the static nature of the quenching process. The superior sensing performance of Film 1 for the analytes in the aqueous phase guarantees that the film may have the potential to be developed into a sensor device for the detection of PA and other NACs in groundwater.