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Analytical Applications of Proton-Transfer Spectroscopy. Detection of Trace Hydrogen-Bonding Impurities in Hydrocarbon Solvents Using 3-Hydroxyflavone as a Fluorescence Probe Pages: 10 Published: Jan 1985
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View License Agreement The photo-excitation steps in 3-hydroxyflavone leading to proton-transfer are described. The consequence of the ultra-rapid (<8 ps) phototautomerization is the emission of a unique yellow-green tautomer fluorescence (λmax 525 nm) in hydrocarbon solution, instead of the violet fluorescence expected from the first UV absorption (onset λ 370 nm, first peak λ 354 nm). The tautomerization is intramolecular, involving the transfer of the hydroxyl hydrogen to the neighboring carbonyl group of the 3-hydroxyflavone molecule. The analytical applications suggested by the qualitative spectroscopic features investigated result from the extreme sensitivity of the intramolecular H-bond to external solvent perturbations, which appear most strikingly in low-temperature spectroscopic studies as induced violet fluorescences of the H-bonded solvates. Using solute concentrations of 10−5 to 10−7 M, H-bonding impurities are detectable at substoichiometric concentrations. In the case of water in hydrocarbon solvents, the present experiments suggest that 10−7 to 10−9 M water may be detectable. Ethers, alcohols, water, and other H-bonding solvents give characteristic violet solvate fluorescence band contours and peak positions, permitting qualitative discrimination of trace contaminants. The use of 3-hydroxyflavone as a fluorescence probe for solvent impurities is suggested. An application is made of isolated-site crystal matrix spectroscopy to determine the intrinsic low-temperature spectroscopic behavior of solutes, such as quinones and ketones, which can H-bond with trace impurities. | ||
