Solvent effect on the relative quantum yield and fluorescence quenching of 2DAM

• Quinine sulfate solution in 0.1 M of H2SO4 is taken as standard reference.
• The relative quantum yield of the solute is more in polar solvents and largest in DMSO.
• The SV plots show positive deviation, indicating efficient fluorescence quenching.
• The value kq is greater than 4πN′R′D in AN, DX, DCE and TOL.
• FSK model helps to recover R′ and D directly from the plots verses [Q]1/3.

The relative quantum yield of diethyl 2-acetamido-2-((3-oxo-3H-benzo[f]chromen-1-yl)methyl) malonate [2DAM] is estimated using single point method with quinine sulfate as standard reference. The quantum yield varies between 0.1161 and 0.3181 depending on the nature of the solvent. The rates of radiative and non radiative decay constants are also calculated. The fluorescence quenching of [2DAM] by aniline is studied at room temperature, by steady state, in five different solvents namely acetonitrile (AN), 1,4 dioxane (DX), 1,2 dichloroethane (DCE), tetrahydrofuran (THF) and toluene (TOL), in order to explore various possible quenching mechanisms. The experimental results show a positive deviation in Stern Volmer plots for all solvents. Various parameters for the quenching process are determined by ground state complex, sphere of action static quenching model and finite sink approximation model. The magnitudes of these rate parameters indicate that positive deviation in the Stern Volmer (SV) plot is due to both static and dynamic processes. Further, finite sink approximation model is used to check whether these bimolecular reactions were diffusion limited or not. The values of distance parameter R′ and diffusion co efficient D are determined and then compared with the values of encounter distance R and diffusion coefficient D calculated using Stokes–Einstein equation.

The relative quantum yield and bimolecular quenching reactions of diethyl 2-acetamido-2-((3-oxo-3H-benzo[f]chromen-1-yl) methyl) malonate [2DAM] are studied. The relative quantum yield is calculated using single point method. It is found that the solute exhibit more fluorescent nature in polar solvents and substitution in 4th position of the solute accounts for more relative quantum yield. The fluorescence quenching is studied in different solvents. The quenching is found to be appreciable and a positive deviation from linearity is observed in the Stern Volmer plot for all the solvents. Various parameters for the quenching process are determined by sphere of action static quenching model and finite sink approximation model. The magnitudes of these rate parameters indicate that positive deviation in the Stern Volmer (SV) plot is due to both static and dynamic processes. The molecular structure of the solute 2DAM is as shown below.Figure optionsDownload as PowerPoint slide