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

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-2hydroxybenzaldehyde 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 (nonpolar), ethyl acetate (moderately polar), methanol (polar protic) and water (highly polar and protic) displayed a bathochromic shift of the absorption (Dl max z 25 nm) and emission (Dl max z 57 nm) bands with increasing solvent polarity. The Dl max of emission is more pronounced than the Dl max 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.

Multiexcitation Fluorogenic Labeling of Surface, Intracellular, and Total Protein Pools in Living Cells

“…Coumarins are benzopyran structures which absorb in the violet region of the visible spectrum and show tunable photophysical properties like quantum yield, extinction coefficient, and photostability. − These attractive features coupled with the demonstrated utility of coumarins for fluorogenic sensing , of different analytes and the ability of a donor to transfer energy to a MG-dL5** acceptor prompted us to synthesize coumarin–MG conjugates. In this article, we demonstrate the use of violet-excited, blue-emitting coumarin-based donor dyes for energy transfer into the secondary excitation band of the MG-FAP complex.…”