An investigation on electron transfer quenching of zinc(II) meso-tetraphenylporphyrin (ZnTPP) by colloidal TiO(2)

Electron transfer and fluorescence “turn-off” based CdTe quantum dots for vancomycin detection at nanogram level in aqueous serum media

Mode of interaction of GSH-CdTe QDs with vancomycin and the mechanism of the fluorescence “turn-off” process.

Contrasting emission behaviour of phenanthroimidazole with ZnO nanoparticles

A new fluorophore 2-(4-fluorophenyl)-1-phenyl-1H-phenanthro [9,10-d]imidazole has been synthesized and characterized by spectroscopic techniques. Nanoparticulate ZnO enhances the fluorescence of the synthesised fluorophore. The absorption, fluorescence, lifetime, cyclic voltammetry and infrared studies reveal that fluorophore is attached to the surface of ZnO semiconductor. Photo-induced electron transfer (PET) explains the enhancement of fluorescence by nanoparticulate ZnO and the apparent binding constant has been obtained. Adsorption of the fluorophore on ZnO nanoparticle lowers the HOMO and LUMO energy levels of the fluorophore. The strong adsorption of the phenanthrimidazole derivative on the surface of ZnO nanocrystals is likely due to the chemical affinity of the nitrogen atom of the organic molecule to the zinc ion on the surface of nanocrystal.

Benzimidazole derivative vs. different phases of TiO2-physico-chemical approach

1-Benzyl-2-phenyl-1H-benzo[d]imidazole (BPBI) has been synthesized by simple steps and characterized by spectral studies. Absorption and fluorescence spectral studies have been employed to investigate the interaction of BPBI with the anatase, hombikat, P25 and rutile phases of TiO2. The emission of the BPBI is efficiently quenched by anatase, hombikat and P25 TiO2 nanoparticles owing to charge injection from the excited singlet state of BPBI to the conduction band of the TiO2 nanoparticles. Surprisingly, rutile phase enhances the fluorescence which is likely due to lowering of LUMO and HOMO levels of the ligand on ducking of the benzimidazole moiety of the BPBI molecule into the void space of rutile TiO2. Electron injection from photoexcited BPBI to the TiO2 conduction band (S*→S(+)+e(-)(CB)) is likely to enhance the fluorescence.

Fluorescence quenching of organic molecule by insulator

A new kind of fluorophore 2-(4-fluorophenyl)-1-phenyl-1H-benzo[d]imidazole (FPPBI) has been synthesized and characterized by (1)H NMR, (13)C NMR, mass spectral studies and single crystal XRD. The energy transfer from FPPBI to Al2O3 nanocrystals has been studied by absorption, fluorescence and lifetime spectroscopic methods. The association between nanoparticles and FPPBI is explained from both absorption and fluorescence quenching data. The distance between FPPBI and Al2O3 as well as the critical energy transfer distance has been deduced.

Studies on the interaction of interface between morin and TiO2

For the first time, the interaction between morin and TiO(2) nanoparticles was investigated by UV-vis absorption, UV-vis diffuse reflectance spectrum, FT-IR, fluorescence, and three-dimensional fluorescence spectra techniques. The results showed that chemical bonds had formed between the surface atoms of TiO(2) nanoparticles and morin molecules. The fluorescence intensity of TiO(2)-morin nanocomposites was much higher than that of morin particles. In addition, the effect of TiO(2) concentrations on the fluorescence intensity of morin was also investigated.

Effect of anchoring group on the photosensitization of colloidal TiO2 nanoparticles with porphyrins

The interaction of porphyrins (TCPP, TSPP, TMeOPP and TPP) with colloidal TiO(2) nanoparticles was studied by infra-red, UV-visible absorption, steady state and time resolved fluorescence spectroscopy. The porphyrins (TCPP, TSPP and TMeOPP) adsorbed on the surface of colloidal TiO(2) nanoparticles through electrostatic interaction. According to absorption and fluorescence changes the apparent association constants (K(app)) were calculated. However, TPP did not interact with surface of colloidal TiO(2) nanoparticles due to the absence of anchoring group. The fluorescence quenching is attributable mainly to electron transfer from the excited state porphyrins to the conduction band of colloidal TiO(2). The rate of electron transfer process (k(et)) was calculated using lifetime measurement. The electron transfer mechanism has been proved by the calculation of free energy change (DeltaG(et)) by applying Rehm-Weller equation. Using all the spectroscopic measurements we confirmed that the presence of anchoring group plays major role in the adsorption as well as the electron transfer processes.