PHYS 131 |
| J-aggregates of cyanine dyes are nanosystems characterized by unique optical properties the origin of which is not yet completely understood. It is well known that the J-aggregation of 1,1'- diethyl-2,2'-cyanine (PIC) iodide can be easily promoted by addition of neutral and basic inorganic salts to the solutions and that the optical properties of PIC J-aggregates depend on the anion of an inorganic salt added. We applied 2-D NMR spectroscopy to investigate possible structural changes of PIC during its J-aggregation in water solutions promoted by addition of different inorganic salts. NMR spectra of all J-aggregated samples studied contained a series of new proton's peaks absent in the spectra of monomers. The most significant changes took place in the aromatic region of the spectra. Though the spectra of the samples containing different inorganic salts were very similar, the positions of the new peaks were affected by an anion of inorganic salt added. This allows to conclude that the J-aggregation of PIC is accompanied by a complexation with an anion of inorganic salt. Analysis of correlation patterns of the 2D NMR spectra of the samples suggested that a portion of structural changes of PIC caused by J-aggregation is similar to those caused by di-protonation. Possible explanations of the structural changes of PIC caused by J-aggregation that could be first responsible for the unique optical properties of J-aggregates are discussed. |
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Spectroscopy, Chemistry, and Imaging through Nanophotonics
8:20 AM-12:00 PM, Monday, April 7, 2008 Morial Convention Center -- Rm. 340/341, Oral
Division of Physical Chemistry |