BENZOTHIAZOLIUM STYRYL DYES CONTAINING A MONOAZACROWN ETHER - PROTONATION AND COMPLEXATION WITH METAL AND AMMONIUM CATIONS IN SOLUTION

Solutions of the trans-isomers of a model benzothiazolium styryl dye a nd two novel derivatives containing monoaza-15-crown-5 and -18-crown-6 ether rings have been studied using UV-VIS absorption spectroscopy. P rotonation of these dyes causes the strongest colour changes, arising from hypsochromic shifts of ca. 140 nm in their absorption band maxima . The azacrown ether dyes have been found to complex alkali-metal (Li, Na+, and K+), alkaline-earth-metal (Mg2+, Ca2+, and Ba2+), and ammon ium (NH4+) cations, but not silver (Ag+), in acetonitrile solution, wh ile of these cations only Ag+ forms a complex in aqueous solution. Spe ctra and stability constants are reported for all of these complexes a nd indicate that the dyes are effective chromoionophores. The stabilit y of the metal cation complexes in acetonitrile solution has been foun d to depend on the presence of trace amounts of water; this effect has been quantified and is interpreted in terms of the competitive solvat ion of these cations by water. The stability constants, spectra, and h ypsochromic shifts together indicate that small cations complex with t he crown ether ring, but not with the azacrown nitrogen atom.