title: Effects of NaCl on the J-aggregation of two thiacarbocyanine dyes in aqueous solutions.
abstract: The effects of NaCl on the aggregation of two typical thiacarbocyanine dyes (3,3'-di(3-sulfopropyl)-4,5,4',5'-dibenzo-9-phenyl-thiacarbocyanine triethyl ammonium salt (Dye 1) and 3,3'-di(3-sulfopropyl)-4,5,4',5'-dibenzo-9-methyl-thiacarbocyanine triethyl ammonium salt (Dye 2)) in aqueous solution have been studied by using absorption spectroscopy, fluorescence spectroscopy, and 1H- and 23Na-NMR measurements. It is found that the J-aggregation of two dyes can be promoted by the addition of NaCl and that the effective coherence length of the J-aggregate is shorter than that obtained without NaCl. Fluorescence spectra demonstrate that the fluorescence intensities of the J-aggregates of two dyes are quenched by addition of NaCl. This is consistent with the decrease of the effective coherence length of J-aggregates of the two dyes in the presence of NaCl. 1H-NMR spectra of two dyes show that the Na(+) ions penetrate into the J-aggregates and replace the counterion (triethylammonium ions) in two dyes. The measurements of the chemical shifts of 23Na nuclei provide further information about the interaction between the Na(+) ions and dye anions in the J-aggregates of the two dyes. Due to this interaction, the electrostatic repulsion between the dye anions in the J-aggregates can be reduced and thus accelerate the aggregation of the two dyes in the presence of NaCl. The apparent association constants between Na(+) ions and dye molecules in J-aggregates of Dye 1 and Dye 2 estimated from the measured chemical shifts of 23Na nuclei are about 2.38 M(-1) and 1.35 M(-1), respectively.
authors.affiliation: Technical Institute of Physics and Chemistry, the Chinese Academy of Sciences, Beijing 100101, People's Republic of China.junfengxiang@yahoo.com
authors.forename: Junfeng
authors.initials: J
authors.lastname: Xiang
authors.forename: Xiaorong
authors.initials: X
authors.lastname: Yang
authors.forename: Ciping
authors.initials: C
authors.lastname: Chen
authors.forename: Yalin
authors.initials: Y
authors.lastname: Tang
authors.forename: Wenpeng
authors.initials: W
authors.lastname: Yan
authors.forename: Guangzhi
authors.initials: G
authors.lastname: Xu
mesh_terms: D002232:Carbocyanines / Q000737:chemistry* / Q000494:pharmacology; D004396:Coloring Agents / Q000737:chemistry* / Q000494:pharmacology; D017666:Deuterium Oxide; D009682:Magnetic Resonance Spectroscopy; D000432:Methanol / Q000737:chemistry; D008956:Models, Chemical; D012965:Sodium Chloride / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence
chemical_list: D002232:Carbocyanines; D004396:Coloring Agents; D012965:Sodium Chloride; D017666:Deuterium Oxide; D000432:Methanol