Effect of Doubly Charged Metal Cations on J-Aggregation of an Anionic Heptamethine Indocyanine Dye

Abstract

The effect of doubly charged metal cations (Mg²⁺, Mn²⁺, Cu²⁺, Ni²⁺, Zn²⁺, Сd²⁺) on J-aggregation of an anionic heptamethine indocyanine dye in aqueous solutions has been studied spectrophotometrically. The equilibria between monomers, dimers, and J-aggregates of the dye in solution have been studied. On the basis of the spectral data, the thermodynamic parameters (equilibrium constants at different temperatures, changes in enthalpy, entropy, and Gibbs energy) have been calculated for the J-aggregation process of the dye, including those in the presence of doubly charged metal cations. It has been established that the metal-complexed J-aggregates of the heptamethine indocyanine dye have narrow excitonic absorption bands with a half-width of 16–20 nm and a maximum at 920 nm. It has been shown that the introduction of doubly charged metal cations into the solution leads to a decrease in the enthalpy and entropy for J-aggregation by 60–100 kJ mol^–1 and 20–100 J mol⁻¹ K⁻¹, respectively.