Aggregation-induced sensitization in aqueous solutions of Al3+-chrome azurol S complexes and ionic liquids based on 1-alkyl-3-methylimidazolium bromide

The dependences of the absorption spectra of chrome azurol S (CAS) and Al3+-CAS complexes on the concentration of ionic liquids (ILs), 1-alkyl-3-methylimidazolium bromide ([C(n)Mim]Br, with n = 8, 10, 12), were measured at 298.15 K in aqueous solutions with pH = 5.6. It is found that ILs can induce the significant red-shifts of the wavelength at the absorption maximum (lambda(max)) of Al3+-CAS complex from 545 to 646 nm for [C(8)Mim]Br, anti to 642 nm for [C(12)Mim]Br and [C(16)Mim]Br, respectively. Accompanying the red-shifts, the absorbance at lambda(max), and thereby molar absorptivity (epsilon), changes markedly with the IL concentration, and consequently the effect of ILs on the absorbance at lambda(max) is systematically investigated in this work. Along with the experimental results of resonance light scattering, the sensitization mechanism is analyzed from the aggregation of the ILs and the interactions of ILs with CAS and Al3+-CAS complexes. It is shown that the hydrophobic interactions of IL subaggregates with CAS in Al3+-CAS complex are the crucial factor for the sensitization. (C) 2010 Elsevier B.V. All rights reserved.