Effect of stereo electronic factors of coumarin derivatives during their interaction with TiO2 nanoparticles

Abstract

The effect of stereo electronic factors of coumarin derivatives, 6-methoxy-4-azido methyl coumarin (6MCA) and 7-methoxy-4-azido methyl coumarin (7MCA) during their interaction with the TiO2 nanoparticles in ethyl acetate, tetrahydrofuran, methanol, dimethyl formamide and acetonitrile solvents has been studied using uv-vis absorption spectroscopy, fluorescence quenching, FRET and electrochemical analysis. Benesi-Hildebrand plots confirm that interaction between 6MCA and TiO2 is stronger in solvents with low dielectric constant whereas for 7MCA and TiO2 system, interaction is stronger in solvents with high dielectric constant. The steady state and time resolved S-V plots are linear for both the systems. For 6MCA system, quenching rate parameter is decreasing with increasing dielectric constant of the solvent and for 7MCA system these values are in increasing order with increasing dielectric constant of the solvents. FRET study also confirms that nature of interaction between these two systems is different. Electrochemical analysis reveals the role of electron transfer from coumarin derivative to TiO2 nanoparticles and shows that azido group (-N3) of 7MCA and 6MCA are responsible for electron transfer. The magnitude of free energy change for electron transfer confirms that quenching is more efficient for 7MCA system. The higher magnitude of quenching rate parameter of 7MCA compared to 6MCA is due to its stable and polar structure.