Influence of inorganic salts and bases on the J-band in the absorption spectra of water solutions of 1,1′-diethyl-2,2′-cyanine iodide

We studied the influence of inorganic salts and bases on the absorption spectra and kinetics of the formation of the J-band in water solutions of 1,1'-diethyl-2, 2'-cyanine (PIC) iodide. The absorption spectra of diluted (10(-5) to 10(-6) mol/L) solutions of PIC containing significant amounts of neutral or basic inorganic salts showed an intense and narrow J-band, with the half-width at the full maximum (HWFM) of less than 4 nm at room temperature. The position of the maximum of the J-band depended on the anion of the salt. Spectra had shape concurrent with that previously assigned in published materials to pure J-aggregates. Kinetics of the absorption spectra during the formation of the J-band in diluted solutions showed isosbestic points, indicating that PIC molecules undergo a transition from monomer state directly to J-aggregate state, without intermediate states, such as dimers or trimers. Absorption spectra of concentrated solutions of PIC containing some inorganic salts showed two J-bands. The red J-band had the maximum at 579 nm in all solutions. The position of the maximum of the blue band depended on the anion of the salt. Its intensity strongly depended on the concentration of the inorganic salt. Possible mechanisms of the influence of inorganic anions on the formation of the J-band in the spectra of diluted and concentrated solutions of PIC are discussed.