Synthesis, characterization of conjugated oligo-phenylene-ethynylenes and their supramolecular interaction with β-cyclodextrin for salicylaldehyde detection

Four new conjugated oligo-phenylene-ethynylenes derivatives, N-methyl-4-(4-acetylthiophenylethynyl)-1,8-naphthalimide (1), thioacetic acid S-[4-(4-aminophenyl-ethynyl)phenyl]ester (2), 4-methylthiophenylethynylbenzenamine (3), N-methyl-4-(4-methyl-thiophenyl-ethynyl)-1,8-naphthalimide (4), were synthesized by Sonogashira and Eglinton cross-coupling reactions. The structures of the four compounds were confirmed by 1HNMR, 13CNMR, MS and IR and their spectral characteristics were studied by ultraviolet and visible (UV) spectroscopy as well as fluorescence spectroscopy in different medium. It was found that the fluorescence properties of compounds 2 and 3 were notably improved in aqueous solutions in the presence of β-cyclodextrin (β-CD). Spectral analysis supported the suppositions that the fluorescence intensity enhancement was due to the formation of inclusion complex with β-CD. The supramolecular interaction was investigated in detail and the reaction mechanism was provided. A salicylaldehyde determination method in aqueous medium was established based on the supramolecular complex of compound 3. Under the optimum conditions, the supramolecular complex exhibited a dynamic fluorescence response range for salicylaldehyde from 0.6 to 240×10−6 molL−1, with a detection limit of 1×10−8 molL−1.