Solvent Effect on Fluorescence Properties of Stilbene Dendrimer Surrounded by Benzyl-Ether Dendrons (original) (raw)
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Tetrahedron, 2013
Different generations of dendrimers incorporating one fluorescent core of apigenin and three Fréchet benzylic dendrons have been prepared. The chief geometric features of these dendrimers have been obtained by Molecular Dynamics simulations. These computational data suggest that the asphericities of dendrimers belonging to the third and fourth generations are considerably larger than those associated with lower radii of gyration. Fluorescence spectra of high generation dendrimers evolve along time and quantum yields show an appreciable lowering for the fourth generation dendrimer. All these data suggest aggregation phenomena and lower quantum yields for nonspheric dendrimers in solution.
Intrinsic Fluorescence of Carboxylate-Terminated Polyamido Amine Dendrimers
Applied Spectroscopy, 2001
The ''intrinsic'' uorescence of carboxylate-terminated polyamido amine (PAMAM-CT) dendrimers is studied by two uorescence techniques-excitation-emission matrices (EEMs) and lifetimes. The EEM s show similar spectral pro les for all dendrimer generations (a broad peak with an excitation and em ission m aximum of 380 and 440 nm, respectively) and an overall increase in relative uorescence emission with increasing generation. Three distinct, fairly discrete lifetimes are also recovered . The shortest lifetime (0.2-0.4 ns) is a background signal from the solvent. The two longer lifetimes are attributed to the dendrimer. There is a general shift to longer lifetimes in t 2 and t 3 , with increasing generation (G n). Both lifetim es nearly double in m agnitude, going from G2.5 to G7.5, which is indicative of a speci c uorescen t component being in a more protected or constrained microenvironment. These results imply that the dendrimer becomes densely packed with increasing generation. The weak, but detectable, uorescence is most likely due to an n ® p * transition from the amido groups throughout the dendritic structure. Even though the exact nature of PA-MAM -CT uorescence is not fully understood, it is clear that this property shows the unique aspects of the architecture of these dendrim ers and can be utilized in their characterization.
Photophysical properties of Newkome-type dendrimers in aqueous medium
Photochemical & Photobiological Sciences, 2007
Newkome-type first, second and third generation dendrimers, having t-butyl (GB), ethyl (GE) and carboxylic (GA) end groups, were synthesized. A pyrene group, which can act as fluorescent sensor, was attached to the core of the dendrimers and their photophysical properties in aqueous solution were studied. These dendrimers were found to aggregate in aqueous solution, which manifested as an excimer peak in the pyrene emission spectra for the first and second generation dendrimers with ethyl and t-butyl end groups. The excimer peak however was not seen in case of the third generation dendrimer. Dendrimers with carboxylic end groups, did not show the excimer peak in water, which implies the hydrophobic nature of the aggregation. It is observed that the intensity of the excimer peak decreases with the increase in the size of the dendrimer. Lifetime studies carried out on the first and second generation dendrimers showed the formation of excimer species as a risetime in the decay curve. The aggregation of the third generation dendrimer was proposed from the quenching studies using silver ions and CCl 4 as quenchers.
Analytica Chimica Acta, 1999
Alternant and nonalternant polycyclic aromatic hydrocarbons (PAHs) are employed to compare carboxylate-terminated polyamido amine (PAMAM) dendrimers to typical anionic micelles. Nitromethane is a known, selective, quenching agent of alternant PAHs. However, recent studies by Acree and co-workers have found that nitromethane will also quench the fluorescence emission intensity of nonalternant PAHs in the presence of anionic surfactants above the critical micelle concentration. The quenching of alternant and nonalternant PAHs by nitromethane is used to compare dendritic 'unimolecular micelles' to traditional micelles. Experimental results indicate that the PAHs' association with these dendrimers does not appear to occur in the 'palisade' region, as seen in traditional micelles, but rather deeper within the dendrimer structure. Solvent polarity probe studies and quenching in the absence of nitromethane also support this conclusion. Due to the fact that the PAHs do not reside near the negatively charged surface groups, the nitromethane selective quenching rule is obeyed in carboxylate-terminated PAMAM dendrimers (10 mM in surface groups).
Incorporation of fluorescent probes into PAMAM dendrimers
Bioelectrochemistry, 2004
Interactions of two fluorescent probes 1-(trimethylammoniumphenyl)-6-phenyl-1,3,5 hexatriene p-toluenesulfonate (TMA-DPH) and 12-(9-anthroyloxy) stearic acid (12-AS) with polyamidoamine (PAMAM) dendrimers were studied. Changes in fluorescence intensity and steady-state fluorescence anisotropy of TMA-DPH and 12-AS were monitored. It was found that 12-AS molecules incorporated into dendrimer cavities whereas TMA-DPH molecules aggregated on the surface of polymer. Dendrimer size had not significant impact on its host properties. D
Study of Poly(amidoamine) Starburst Dendrimers by Fluorescence Probing
Langmuir, 1997
The binding of fluorescent probe molecules to poly(amidoamine) starburst dendrimers of generations G-0, G-1, and G-2 was investigated. The solubilizing capability of these new materials, in aqueous media, increases with increasing degree of their generation. Pyrene fluorescence however undergoes significant quenching in the solubilized state. In the higher generations, G-1 and G-2, excimer fluorescence was observed even at [pyrene]/[dendrimer] ratios as low as 10-3 .