Role of Substituent Position in Coumarin Derivatives during their Interaction with TiO2 Nano Particles

The effect of position of benzo group in coumarin derivatives, 5,6 benzo-4-azidomethyl coumarin (5BAMC) and 7,8 benzo-4-azidomethyl coumarin (7BAMC) during their interaction with TiO 2 nanoparticles in ethyl acetate, tetrahydrofuran, butan-1-ol and acetonitrile solvents has been studied using different spectroscopic methods and electrochemical analysis. Benesi-Hildebrand plots indicate that nature of interaction between 7BAMC and TiO 2 is 1:2 in solvent with low dielectric constant whereas for 5BAMC and TiO 2 , it is 1:1 in all the solvents. From the fluorescence quenching study and binding equilibria analysis, it is observed that interaction between 5BAMC and TiO 2 depends on the dielectric constant of the solvent. Time resolved quenching study reveals that quenching is dynamic for 5BAMC in solvent with high dielectric constant. Whereas for 7BAMC, it is dynamic in solvent with low dielectric constant. Hence the nature of interaction of these two coumarin derivatives with TiO 2 NPs is different. From electrochemical analysis, it is observed that, free energy change for electron transfer is more negative for 5BAMC-TiO 2 compared to 7BAMC-TiO 2 therefore quenching is more efficient for 5BAMC-TiO 2 compared to 7BAMC-TiO 2 system, which is also confirmed from fluorescence quenching studies. Non-radiative energy transfer rate is more than radiative energy transfer rate for both the systems according to FRET study.