Investigation of the acid-base properties of 2-[2-(4-methoxy-phenylamino)- vinyl]-1,3,3-trimethyl-3H-indolium reagent

The acid-base properties of 2-[2-(4-methoxy-phenylamino)-vinyl]-l,3,3-trimethyl-3H-indolium dye were investigated. The reagent exists in a reactive single charged form over a wide range of acidity, from pH 8 to -2.5 H 0 . The optimum analytical wavelength of the single charged form is 412 nm, where the molar absorptivity is 4.06 x 10 4 dm 3 mol¯ 1 cm¯ 1 Mechanisms of protonation and hydrolysis were discussed. The results suggest the applicability of the dye as an effective analytical reactant. Quantum chemical calculations of the structural and spectral properties of the dye were also carried out.