Azonium-Ammonium Tautomerism and Inclusion Complexation of 1-(2,4-diamino phenylazo) Naphthalene and 4-aminoazobenzene

Abstract

Spectral characteristics of 1-(2,4-diamino phenylazo) naphthalene (FBRR, fat brown RR) and 4-aminoazobenzene (AAB) have been studied in various solvents, varying hydrogen ion concentrations and in β-cyclodextrin (β-CD). The inclusion complex of FBRR and AAB with β-CD were analysed by UV-visible, fluorometry and CAche-DFT methods. Solvent study reveals that only azo tautomer is present in both compounds and the large red shifted absorption and emission maxima of FBRR indicate naphthalene ring effectively increases the π-π* transition. Unusual red shift is observed in acid solutions suggests azonium-ammonium tautomer is present in both molecules. In β-CD solutions, the large hypsochromic shift is observed in S(0) and S(1) states indicates ortho amino group of FBRR molecule is entrapped in the β-CD cavity and the large bathochromic shift for AAB in the S(1) state indicates 1:1 inclusion complex is formed.

Nanorod formation of cyclodextrin-covered sudan dyes through supramolecular self-assembly

“…The observed spectral changes are interpreted in terms of azo-hydrazo equilibrium. [24][25][26][27] The above results confirmed that increasing the polarity of solvents leads to larger amount of the 'hydrazo' form, than that of the 'azo' form. [32,33] The spectral maxima also show that methyl substituent hardly affects the position of the azo-hydrazo tautomeric equilibrium compared to hydroxyl substituent.…”

“…The small increase in the absorption with the addition of both CDs has been attributed to the improved dissolution of the guest molecules through the detergent action of CDs. [24][25][26][27][28] Emission spectra monitored at two different excitation wavelengths (350 and 510 nm) are displayed in Figures 3 and 4. The emission spectra at λ exc $ 350 nm are different than that at λ exc $ 510 nm.…”

“…Thus, the polarity and viscosity variations may not play an important role in both dyes. [24][25][26][27][28] The binding constant for the 1:1 and 1:2 inclusion complex formations were calculated using Benesi-Hildebrand equation. [30] It apparently explains that SDIII and SDIV form 1:2 inclusion complexes with both CDs.…”

“…[24][25][26][27] However, in SDIII:CD complexes the phenyl rings (C, D) are partially present in one of the CD cavity and naphthol ring is (D ring only) partially encapsulated in another CD cavity, whereas the hydroxy group is present out side of the CD cavity. The above discussions imply that both dyes form similar types of 1:2 inclusion complexes with a-CD and b-CD which led to the self-assembly of nanostructures.…”

“…In all solvents, when compared to sudan I (SDI) and sudan II (SDII) [24][25][26][27] $ 620, 561 nm). The large red shift and broad absorption and emission spectra suggest intramolecular hydrogen bond (IHB) or intramolecular proton transfer (IPT) present in sudan dye molecules.…”