Temperature and Concentration-Dependent Absorption and Fluoresence of Thaits J-Aggregate Dye, Reveal Supra-Molecular Architecture

University essay from Lunds universitet/Kemiska institutionen

Author: Michael Kontaiteh Fonjang; [2012]

Keywords: Kemisk fysik; Chemistry;

Abstract: The narrow and redshirted absorption bands of J–aggregates relative to the monomer absorption, coupled with their ability to coherently and incoherently delocalise exciton wave function over several hundreds of molecules has made this class of molecules very important in high technology fields. This has provided new impetus to study the properties of J–aggregates and to explore the mechanism involved in their production. We have investigated the absorption and fluorescence of THIATS J-aggregate dye as a function of Temperature and concentration in aqueous solotion.1mL of 1M solution of sodium chloride was added to each monomer solution to enhance aggregation. The formation of a beautiful intense blue colour and a shift of the absorption band from 515nm to 625nm is a tremendous indication that the THIATS monomers aggregate in aqueous solution. The monomer spectra show no fluorescence peak, while the aggregate spectra show a fluorescence peak at 638nm.Plots of absorption and fluorescence graphs show that stokes shift decreases with concentration. The temperature–dependent absorption spectra show an isobestic point at λ=530nm, which indicates an equilibrium situation between monomer and aggregate. From the data obtained, we calculated an aggregation number (n=4), an equilibrium constant(K=3.067M-1), and Gibbs free energy (ΔG=-2.925KJ/mol).Furthermore, we calculated the Gibbs free energy required to construct one supramolecule of THIATS aggregate (5'10-21J), and compared it with the thermal energy per molecule (4.39'10-21).Consequently, our experiments have shown that they are comparable. A possible improvement on the properties of THIATS J-aggregate may be the synthesis of derivatives that will enhance its ability to delocalize exciton energy, and consequently better its application in high technology fields.

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