Spectroscopic behavior of 1,1′-diethyl-2,2′-dicarbocyanine iodide in ethanol/water solutions with high ionic strength

Absorption spectra of 1,1'-diethyl-2,2'-dicarbocyanine iodide (DDI) have been obtained in ethanol/water mixtures. Increase of ionic strength obtained by addition of salts (e.g. NaCl) to the solvent mixture containing 10% of H2O and 90% of EtOH leads to appearance of a new absorption band at 849 nm. Intensity of this band increases with salt concentration which suggests that this spectral feature is related to a DDI aggregate. However, no emission has been observed with excitation at 850 nm indicating that this feature does not correspond to a J-type aggregate. Addition of NaCl to DDI solutions possessing the EtOH/H2O (v:v) ratio different from 1:9 does not induce appearance of the new absorption band. (C) 2002 Elsevier Science B.V. All rights reserved.