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A new coumarin derivative, (E)-3-(3-(4-(dimethylamino) phenyl) acrylo-yl)-4-hydroxy-2H-chromen-2-one (3), was synthesized by the condensation of 3-acetyl-4-hydroxycoumarin (1) with 4-N,N-dimethylaminobenzaldehyde (2) in the presence of piperidine in ethanol. The structure of the synthesized compound was characterized using spectroscopic data (IR and 1H NMR) and elemental analysis. The antimicrobial properties and acetylcholinesterase inhibition activity (AChEI) of coumarin 3 were investigated, with the highest observed AChEI activity providing 48.25% inhibition. The electronic absorption and emission spectra revealed that 3 exists as two, main keto-enol tautomers. The ratios of these tautomers in both protic and aprotic solvents with different polarities and dielectric constants were calculated. The fluorescence of coumarin 3 was enhanced upon increasing the medium viscosity, which was due to the resultant molecular rigidity. This criterion was further investigated using DNA, whereby 3 showed enhanced fluorescence upon its uptake in DNA grooves and was therefore tested as a novel DNA fluorescent stain.

The electronic absorption, emission spectra as well as fluorescence quantum yields of some coumarin derivatives were measured in different solvents of different polarities. pKa and pKa* were calculated using universal buffers.The dyes undergo micellization in different micelles and may be used as a probe to determine the critical micelle concentrations (CMC) of CTAB and SDS. The effect of metal ions like [Cu +2 , Co +3 , Ni +2 ] as quenchers and the effect of temperature on quenching are studied and thermodynamic parameters have been calculated.