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Issue 22, 2014
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Synthesis, characterization and spectroscopic properties of water soluble coumarins substituted with oligomeric alkoxy functions

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Abstract

Novel water soluble robust fluorescent coumarins substituted with oligomeric alkoxy functions were synthesized by incorporating the Blaise reaction in the key step. Mono-methylated oligomeric polyethylene glycols were subjected to a three step protocol, namely (i) Michael addition to acrylonitrile, (ii) Blaise reaction with ethyl bromoacetate and (iii) condensation with 4-N,N-diethylamino-2-hydroxybenzaldehyde to give fluorescent water soluble coumarins. Water solubility of the coumarins increased with the number of oxygen atoms in the side chain. However, even the most water soluble coumarin in this series can be readily extracted out of water with organic solvents like dichloromethane or ethyl acetate. Both absorption and emission spectra, recorded in four solvents, namely, hexane (non-polar), ethyl acetate (moderately polar), methanol (polar protic) and water (highly polar and protic) displayed a bathochromic shift of the absorption (Δλmax ≈ 25 nm) and emission (Δλmax ≈ 57 nm) bands with increasing solvent polarity. The Δλmax of emission is more pronounced than the Δλmax of absorption, which indicates intramolecular charge-transfer (ICT) is less in the ground state compared to the excited state. Emission spectra recorded in these four solvents showed that fluorescent intensity is maximum in ethyl acetate.

Graphical abstract: Synthesis, characterization and spectroscopic properties of water soluble coumarins substituted with oligomeric alkoxy functions

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Supplementary files

Article information


Submitted
15 Nov 2013
Accepted
08 Jan 2014
First published
17 Feb 2014

RSC Adv., 2014,4, 11064-11072
Article type
Paper

Synthesis, characterization and spectroscopic properties of water soluble coumarins substituted with oligomeric alkoxy functions

H. Surya Prakash Rao, M. Babu and A. Desai, RSC Adv., 2014, 4, 11064
DOI: 10.1039/C3RA46704J

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