Bimolecular fluorescence quenching reactions of the biologically active coumarin composite 2-acetyl-3H-benzo[f]chromen-3-one in different solvents.

A study on fluorescence quenching was carried out for the coumarin derivative 2-acetyl-3H-benzo[f]chromen-3-one (2AHBC) with aniline at room temperature. Efficient fluorescence quenching was observed and Stern-Volmer (S-V) plots showed upward curves from linearity in all solvents of different polarities. For the solute 2AHBC, ground state complex formation does not hold in our study. The kinetic distance (r) value was found to be greater than the encounter distance (R) and indicated that the quenching reaction was held within the sphere of action. Diffusion-limited reactions were found to be more prominent in high polarity solvents, namely dimethyl sulfoxide (DMSO), DMF, ACN, methanol, ethanol, propanol and DCM. The relationships between quenching constant (KSV ) and dielectric constants (ε) of the different solvents were studied.