Spectroscopic Characterization of Solvatochromic Dyes

Abstract

Linear solvation energy relationships (LSERs) are used to quantify the intermolecular interactions between solvents and several organic dyes – di-8-ANEPPS, Coumarin 30, Coumarin 153, and 6-hydroxyflavone. LSERs evaluate the sensitivity of a dye’s frequency of maximum absorbance, nmax, to solvent acidity (), basicity (β), polarity/polarizability (π*), and excess polarizability (E). The 34 quantification of the sensitivity of a dye to these parameters (, β, π*, and E) allows for the characterization of a dye’s ability to interact through hydrogen bond accepting, hydrogen bond donating, dipole-dipole interactions, and excess polarizability, respectively. UV-visible spectroscopy is used to measure the wavelength of maximum absorbance of each dye solvent pair. These wavelengths are used to develop an LSER for each dye. The regression analysis for Coumarin 30 data yields the LSER equation max = 26.75 – (0.93 ± 0.10) π* - (0.55  0.05) + (0.12  0.07) βπ – (0.35  0.12)E. The equation shows a large shift in Coumarin 30’s max to lower frequencies attributed to the solvent’s polarity and the solvent’s ability to donate a hydrogen bond. This data suggests that Coumarin 30 has a greater separation of charge in its excited state than its ground state. The results for di-8-ANEPPS show that increasing solvent acidity and solvent polarity decrease the frequency of maximum absorption. This means di-8-ANEPPS is a better hydrogen bond donor as well as more polar in the excited state relative to when it is in its ground state. LSERs for the other dyes will also be presented. Because the dyes’ sensitivities to their chemical environment will be known from the LSERs, they will then be used to characterize system such as surfactant solutions that are used to enhance oil recovery for reservoirs.