Fluorescence chemosensors from conjugated phenylene ethynylene compounds containing salicylaldehyde group for anion detection

Abstract

The new fluorescence molecules PPE I - PPE IV and PE I and OE II, containing salicylaldehyde group as a receptor unit are prepared and the sensing ability toward CN are investigatigated. The homopelymer PPE I –II and random copolymer III are prepared from calcium carbide as the acetylene source while the alternate copolymer PPE IV are prepared from corresponding diyne derivative. The molecular of PPEs are determined with GPC showing in the range of 6.21x10³ - 1.86x10⁴ Da. On the On the other hands, the small molecule PE I and PE II are prepared by Sonogashira coupling reaction to give the yellow solid in 44 % and 42% yield, respectively. The NMR spectroscopy and mass spectrometry data confirm the structures of PE I and PE II. The photophysical properties of PPEs and PEs showed absorption at ca. 315-457 nm and emission at 363-508 nm. However, the fluorescence sensing ability of PPE II, III and IV toward a variety of 12 anions shows small fluorescence enhancement signal in mixture of THF/ aqueous HEPES buffer. In case of PPE I, the addition of NaCN solution at 1 mM concentration increases the fluorescence signal of PPE I giving 1/10 ratio = 9.69. However, due to its poor solubility of PPE I, the sensing ability cannot be quantified and further investigated. In case of small molecule, PE I shows fluorescence enhancement specifically toward CN with the detection limits of 2.5 µM while PE II gave a lower selectivity upon testing with the same set of anions. Interestingly, PR II shows specific fluorescence enhancement with F over other halide ion with the detection limits of 30 µM. These results suggest the high potential use of PPE I and PE I for the detection of cyanide ion while the identification of F from other halide ion can be done with PE II.