Thiophene-thiazole functionalized oligomers-excellent fluorescent sensing and selective probe for copper and iron ion

This paper reports the fluorescent and colorimetric sensing of Cu2+ and Fe2+ using thiophene-thiazole functionalized conjugated oligomers from water samples. Oligomers namely, oligo-4,5-bis-{2-[5-(2-thiophene-2-yl-vinyl)thiophene-2-yl]-vinyl}-thiazole (OBTV-TZ) and oligo-2,4,5-tris-{2-[5-(2-thiophene-2-yl-vinyl) thiophene-2-yl]-vinyl}-thiazole (OTTV-TZ) were synthesized through Wittig condensation and confirmed from FT-IR, 1H NMR and LCMS analysis. The effects of the thiophene and thiazole rings in the oligomer towards metal ion sensing applications were systematically investigated. The color of both oligomers was changed from pale yellow to pale green and dark yellow by the addition of Cu2+ and Fe2+ ions respectively. Upon adding Cu2+ and Fe2+, both sensors displayed a new absorption peak at around 207 nm which forms hyper and hypochromic effects. The detection limit (LOD) of Cu2+ for OBTV-TZ and OTTV-TZ was 1.04 and 0.988 × 10−5 M respectively. Both oligomers were successfully regained from the Fe2+ coordinated system by adding of EDTA. A high selectivity of Cu2+ and Fe2+ using these oligomers in a competent environment of several other metal ions was successfully observed. The electrochemical studies revealed that HOMO and LUMO values of the oligomers increased after mixing with Cu2+ and Fe2+. The LUMO value of the oligomer (OTTV-TZ) was sensed to −3.35 and −3.15 eV after incorporating Cu2+ and Fe2+. Both oligomers exhibited wide pH response in absorbance (pH = 5-10) and fluorescence intensities (pH = 2-9).