Carbazole-containing conjugated copolymers as colorimetric/fluorimetric sensor for iodide anion

Abstract

A series of conjugated poly(p-phenylene carbazole) copolymers, poly(N-hexyl-3,6-carbazole-alt-2,5-bisdodecyloxyphenylene) [P1], poly(N-ethylhexyl-3,6-carbazole-alt-2,5-bisdodecyloxyphenylene) [P2], and poly(N-dodecyl-3,6-carbazole-alt-2,5-bisdodecyloxyphenylene) [P3] were prepared by using palladium-catalyzed Suzuki coupling reactions. All copolymers were characterized by means of FT-IR, GPC, 1H and 13C NMR, UV-vis, fluorescence spectroscopy, and X-ray powder diffraction patterns. All copolymers were soluble in common organic solvents, exhibited good thermal stability up to 390 °C, and showed UV-vis absorbance and fluorescence maxima around 328 and 394 nm, respectively. The polymers P1-P3 differed in N-alkyl substitution, i.e., n-hexyl (for P1), n-ethylhexyl (for P2), and n-dodecyl (for P3) groups. In addition, a third monomer, 2,5-substituted pyridine for poly(N-ethylhexyl-3,6-carbazole-co-2,5-didodecyloxy phenylene-co-2,5-pyridine) (P4) and dialkylated fluorene for poly(N-ethylhexyl-3,6-carbazole-co-2,5- didodecyloxy phenylene-co-9,9′-dihexylfluorene) (P5) was incorporated into the copolymer P2 to investigate the influence on their optical properties. The UV-vis and fluorescence maxima of P4 and P5 showed significant red shift in λmax by 29 and 19 nm and Δλem of 38 and 21 nm, respectively as compared to the polymers P1-P3. The quantum efficiencies of these polymers (52-78%) were relatively higher and may have good applications in the fabrication of LEDs. The UV-vis and fluorescence spectra of the polymers were significantly affected by the addition of tetrabutylammonium iodide and other metal iodides. A colorless polymer solution turns to deep yellow color on the addition of iodide salts. This change is, however, not observed in the presence of other anions such as fluoride, chloride and bromide salts. Therefore, the polymers P1-P5 may be useful in fabricating selective iodide sensors. © 2006 American Chemical Society.