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

Abstract

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.

Protonation of Patented Blue V in aqueous solutions: theoretical and experimental studies

“…Semi-empirical and DFT studies on similar dyes containing C, H, N, O, S have previously been reported in the literature. 10,30,31 PBV contains two sulfo groups (strongly acidic), one OH phenolic group (weakly acidic) and two diethylamino groups, which also could act as an acid when protonated. Due to the presence of non-identical reactivity centers in the dye, it is important to consider the protonation/deprotonation of each acidic group and nitrogen atoms in order to determine the preferred protonation site.…”