Effect of TiO2 nanoparticles on some photophysical characteristics of ketocyanine dyes

The effect of titanium dioxide (TiO₂) nanoparticles (NPs) on photophysical characteristics of 2,5‐di[(E)‐1‐(4‐dimethylaminophenyl) methylidine]‐1‐cyclopentanone (2,5‐DMAPMC) and 2,5‐di[(E)‐1‐(4‐diethylaminophenyl)methylidine]‐1‐cyclopentanone (2,5‐DEAPMC) ketocyanine dyes has been studied using absorption, steady‐state and time‐resolved fluorescence spectroscopy. The magnitudes of association constants determined based on modified absorption spectrum of dyes due to the presence of TiO₂ NPs indicate the interaction of TiO₂ NPs with dye molecules. The quenching of fluorescence intensity of dyes by TiO₂ NPs is observed and it follows linear Stern‐Volmer (S‐V) equation. The magnitude of quenching rate parameter suggests the involvement of static quenching mechanism. The involvement of electron transfer process in reducing fluorescence intensity of dyes has been discussed. Also, varying influence of TiO₂ NPs on two dyes is explained based on the presence of different alkyl substituent in two dyes.     

Effect of Plasmonic Silver Nanoparticles’ Size on Photophysical Characteristics of 4-Aryloxymethyl Coumarins

The effect of plasmonic silver nanoparticles’ size on photophysical characteristics of four biologically active 4-aryloxymethyl coumarins 4-p-tolyloxymethylbenzo[h] coumarin (4PTMBC), 1-(4-iodo phenoxymethyl)-benzo [f] coumarin (1IPMBC), 4-(4-iodo-phenoxymethyl)-benzo [h] coumarin (4IPMBC), and 4-(4-iodo-phenoxymethyl)- 6-methoxy coumarin (4IPMMC) has been studied using absorption and fluorescence spectroscopy. The size of silver nanoparticles has been estimated by field effect scanning electron microscope technique. The absorption maxima of silver nanoparticles are red shifted with increase in their size. The absorption spectral changes of investigated coumarins with the addition of silver nanoparticles of different sizes suggest their possible interaction with silver nanoparticles. Fluorescence quenching has been observed for all the coumarins with the addition of silver nanoparticles of different sizes. The Stern-Volmer (S-V) plots of fluorescence quenching are found to be linear. The magnitude of quenching rate parameter suggests the involvement of static quenching mechanism. Fluorescence data has been used to estimate binding constants and the number of binding sites. The contribution of diffusion and electron transfer processes in fluorescence quenching mechanism has also been discussed. The values of S-V constant and quenching rate parameter are found to decrease with increase in size of silver nanoparticles.