Spectroscopic study of anthraquinone dye/amphiphile systems in binary aqueous/organic solvent mixtures

The absorption spectra of novel dye/amphiphile systems, in which the dye is a 1,5-bis-(R-phenylamino)anthraquinone [R = o-methoxy, o-ethoxy, H] and the solvents are either organic or H2O/organic solvent mixtures, have been investigated. It was found that an abrupt λmax shift of more than 80 nm occurred for the system containing dye having R = o-methoxy and the amphiphile (poly-bis-(2,2′-dimethyl-5,5′-disulphonate)naphthylmethane disodium salt) in pure solvents with a specific ET(30) value or in H2O/DMF (N,N-dimethylformamide) mixtures containing at least 38% water. This type λmax shift was not observed when solvent mixtures containing the other two dyes were studied. The origin of the pronounced λmax shift is discussed in detail. It is believed that this shift arises mainly from changes in the solvation state of hydrophobic dye having R = o-methoxy when water is introduced in the presence of a dispersing agent. In this regard, dye is converted from the monomolecular state to dispersed particles.

► Abrupt and pronounced λmax change of anthraquinone dye/amphiphile systems.
► The abrupt change occurred in pure solvents with a specific ET(30) value.
► The abrupt change also occurred in H2O/solvent mixtures at varying water contents.
► This shift arises mainly from changes in the solvation state of hydrophobic dye.