Coumarins, are widely used as dyes in different industrial processes and are found in wastewater as a contaminants. Coumarins possess significant photophysical and photochemical properties and good solubility. Therefore fluorescence spectroscopy can be an effective tool for its identification water. All chemicals including Coumarin-1 (4 - Methyl-7-Diethylamino coumarin) and Coumarin-2 (7-Ethylamino-6-methyl-4–methyl coumarin) was purchased from Sigma Aldrich of high purity. The fluorescence was examined by fluorescence spectrophotometer (F2700, Hitachi, Japan). The computational simulations were calculated by Gauss View-6 software, and Gaussian 16, to generate the molecular structures. The TD-DFT and DFT theory for fluorescence was done by 6-31 G (d,p) basis set & the B3LYP functional. These compounds demonstrated longer EX wavelength from 350nm and longer EM wavelength over 430nm. The difference of fluorescence EX and EM wavelengths for all compounds is represented as coumarin-1, EX/EM 375nm/456nm, coumarin-2, EX/EM 365nm/470nm (Fig.1). The EX/EM wavelength region for coumarins, is displayed in humic-like region with strong fluorescent signals. The fluorescence coumarins in aqueous solution showed a good linear correlation between concentration and fluorescence intensity with value of R2 as 0.999. The fluorescence EX/EM peak location remains same at all concentrations (µg/L) in water. The substitution of methyl group substitution on the heterocyclic ring at coumarins tends to maintain excitation from 340nm to 375nm and emission wavelength remains 440nm to 470nm. These results indicate that ethylamino substitution at the aromatic ring with methyl amino tends to produce longer excitation and redshift the emission wavelength. This phenomenon is due to the difference in electron donner ability (C2 H5 &gt; C H3). The theoretical results are in line with experiments. The photophysical properties of these compounds are helpful in its identification in water.

Photophysical properties of coumarin-1 and coumarin-2 in water

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ACS Spring 2020 National Meeting & Expo

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