Study on Thermodynamics of Three Kinds of Benzindocarbocyanine Dyes in Aqueous Methanol Solution

• Published in: Bulletin of the Korean Chemical Society Vol. 30; no. 3; pp. 556 - 560
• Main Authors: Huang, Wei, Wang, Lan-Ying, Fu, Yi-Le, Liu, Ji-Quan, Tao, You-Ni, Fan, Fang-Li, Zhai, Gao-Hong, Wen, Zhen-Yi
• Format: Journal Article
• Language: Korean
• Published: 2009
• Subjects: Benzindocarbocyanine dye; Aggregation state; Thermodynamic property
• ISSN: 0253-2964; 1229-5949

Aggregation behavior of three kinds of benzindocarbocyanine dyes in aqueous methanol solution was studied by UV-Vis absorption spectrum. The results indicated that the three dyes all existed monomer-dimer equilibrium in aqueous methanol solution (concentration range $10^{−5}\;to\;10^{−6}$ M) at 25.0$\sim$41.0 ${^{\circ}C}$ for Dye 1, 28.0$\sim$49.0 ${^{\circ}C}$ for Dye 2 and 26.0$\sim$47.0 ${^{\circ}C}$ for Dye 3. The fundamental property of the three dyes as the dimeric association constant KD, the dimeric free energy ${\Delta$}G_D, the dimeric entropy ${\Delta$}S_D, and the dimeric enthalpy ${\Delta$}H_D were determined. The ${\Delta$}H_D of three dyes: Dye 1, Dye 2 and Dye 3 was -42.5, -15.1 and -18.9 kJ/mol, respectively. The experimental observations were the subject of a theoretical study including the ground-state geometries which were fully optimized using DFT at B3LYP/6-31G level. The effect of dye molecule structure on ${\Delta$}H_D was discussed by theoretical calculations.