Spectroscopic investigations on the interaction of biologically active 4-aryloxymethyl coumarins with TiO2 nanoparticles

Abstract

The interaction of four biologically active 4-aryloxymethyl coumarin dyes 4-p-tolyloxymethyl-benzo[h]coumarin (4PTMBC), 1-(4-iodophenoxymethyl)-benzo[f]coumarin (1IPMBC), 4-(4-iodo-phenoxymethyl)-benzo[h]coumarin (4IPMBC) and 4-(4-iodo-phenoxymethyl)-6-methoxy coumarin (4IPMMC) with colloidal TiO2 nanoparticles has been investigated using absorption, steady state and time resolved fluorescence. The size of TiO2 nanoparticles has been found to be 50nm from SEM measurements. The absorption spectral changes of dyes in the presence of TiO2 nanoparticles suggest their possible interaction. The apparent association constants of the interaction are estimated using Benesi-Hildebrand model. Fluorescence quenching has been observed for all the dyes with the addition of colloidal TiO2 nanoparticles and Stern-Volmer plots of fluorescence quenching are found to be linear. The magnitudes of quenching rate parameter and fluorescence lifetime measurements indicate the presence of static quenching mechanism. The binding constants and the number of binding sites have been estimated from fluorescence data. The role of electron transfer process in fluorescence quenching mechanism has been discussed.