Structure and properties of 2-[(E)-2-(4-dipropylaminophenyl)-1-ethenyl]-1,3,3-trimethyl-3H-indolium chloride

The structure of styryl dye, 2-[(E)-2-(4-dipropylaminophenyl)-1-ethenyl]-1,3,3-trimethyl-3H-indolium chloride (I), was investigated using methods such as UV-VIS, fluorescence spectroscopy, and NMR (1H, 13C, APT, HMQC, COSY) and also by examining its electrochemical properties. A study of the acid-base properties revealed the existence of three different forms of the dye. The mechanisms of protolysis and hydrolysis are discussed. The reagent exists in a reactive single-charged form I + over a wide range of acidity (pH 4–11). The optimum analytical wavelength of the singlecharged form is 550 nm, where the molar absorptivity is 5.51 × 104 L mol−1 cm−1. The values of the optimum analytical wavelength and molar absorptivity of the protolysed and hydrolysed forms are: λ max(I-H2+) = 380 nm, ɛ(I-H2+) = 2.01 × 104 L mol−1 cm−1; λ max(I-OH) = 320 nm, ɛ(I-OH) = 1.12 × 104 L mol−1 cm−1. A theoretical study of the spectral and chemical properties of I was carried out by performing quantum chemical calculations.