1,721,016 research outputs found
Luminescent lanthanide ions hosted in a fluorescent polylysin dendrimer. Antenna-like sensitization of visible and near-infrared emission
No full textWe have investigated the complexation of the luminescent Nd3+, Eu3+, Gd3+, Tb3+, Er3+, and Yb3+ ions by a polylysin dendrimer containing 21 amide groups in the interior and, in the periphery, 24 chromophoric dansyl units which show an intense fluorescence band in the visible region. Most of the experiments were performed in 5:1 acetonitrile/dichloromethane solution at 298 K. On addition of the lanthanide ions to dendrimer solutions, the fluorescence of the dansyl units is quenched; in Nd3+, Er3+, and Yb3+, a sensitized near-infrared emission of the lanthanide ion is observed. At low metal ion concentrations, each dendrimer hosts only one metal ion and when the hosted metal ion is Nd3+ or Eu3+, the fluorescence of all the 24 dansyl units of the dendrimer is quenched with unitary efficiency. Quantitative measurements were performed in a variety of experimental conditions, including protonation of the dansyl units and measurements in rigid matrix at 77 K where a sensitized Eu3+ emission could also be observed. The results obtained have been interpreted on the basis of the energy levels and redox potentials of dendrimer and metal ions
Fluorescent guests hosted in fluorescent dendrimers
No full textWe have investigated the formation of host-guest complexes between dendrimers of the poly(propylene amine) family functionalized with dansyl units at the periphery (hosts) with dye molecules (guests). Each dendrimer nD, where the generation number n goes from 1 to 5, comprises 2′′+1 (i.e. 64 for 5D) dansyl functions in the periphery and 2′′+1 -2 (i.e. 62 for 5D) tertiary amine units in the interior. The most thoroughly investigated systems were those with eosin as a guest. The results obtained show that: (i) the nD dendrimers dissolved in dichloromethane solution extract eosin from aqueous solutions; (ii) the maximum number of eosin molecules hosted in the dendrimers increases with increasing dendrimer generation, up to a maximum of 12 for the 5D dendrimer; (iii) the fluorescence of the peripheral dansyl units of the dendrimers is completely quenched via energy transfer by the hosted eosin molecules; (iv) the fluorescence of the hosted eosin molecules is partially quenched; (v) the eosin molecules can occupy two different sites (or two families of substantially different sites) in the interior of the dendritic structure; (vi) excitation of eosin hosted in the dendrimers causes sensitization of the dioxygen emission via eosin triplet excited state. The behavior of fluorescein and rose bengal is qualitatively similar to that of eosin, whereas naphthofluorescein is not extracted. The maximum number of dye molecules extracted by the 4D dendrimer is 25 for rose bengal and ca. 1 for fluorescein, showing that the formation of host-guest species is related to the electronic properties rather than to the size of the dye molecules. © 2002 Elsevier Science Ltd. All rights reserved
Eosin molecules hosted into a dendrimer which carries thirty-two dansyl units in the periphery: A photophysical study
No full textEosin in dendrime
Light-harvesting dendrimers: Efficient intra- and intermolecular energy-transfer processes in a species containing 65 chromophoric groups of four different types
No full textAn eosin molecule encapsulated into the dendrimer shown in the picture collects electronic energy from all 64 chromophoric units of the dendrimer, which comprises three different types of chromophore. Efficient intramolecular (within the dendrimer) and intermolecular (dendrimer-host→eosin-guest) energy-transfer processes by a Förster type mechanism, as suggested by the strong overlap between the emission and absorption spectra of the relevant donor and acceptor units
A dendritic antenna for near-infrared emission of Nd3+ ions
No full textAn interior of 18 amide groups and a periphery functionalized with 24 dansyl groups forms a light-harvesting dendrimer which features intense absorption bands in the near-UV spectral region and a strong fluorescence band in the visible region. Upon encapsulation of Nd3+ ions, the fluorescence of the dansyl groups is quenched and an intense sensitized near-infrared emission of Nd3+ is observed. The associated energy transfer is shown in the cartoon
Photochemical and photophysical properties of poly(propylene amine) dendrimers with peripheral naphthalene and azobenzene groups
No full textWe report the preparation, the absorption spectra, and the photophysical and photochemical properties in dichloromethane solution of four dendrimers of the poly(propylene amine) family (indicated by POPAM or PPI) functionalised with naphthalene and trans-azobenzene units. Each dendrimer Gn, where n = 1 to 4 is the generation number, comprises 2n+ 1− 2 (i.e., 30 for G4) tertiary amine units in the interior and 2n+ 1 (i.e., 32 for G4) naphthalene and trans-azobenzene units in the periphery. For comparison purposes, the photophysical and photochemical properties of model compounds of the peripheral units have also been investigated. We have found that the fluorescence of the naphthalene units is quenched by the tertiary amines (via electron transfer) as well as by the trans-azobenzene units (via energy transfer). The quantum yields of the trans→cis and cis→trans photoisomerisation of the azobenzene units have been measured at various excitation wavelengths. Quenching of the fluorescence of the excited naphthalene unit by the trans- and cis-azobenzene units is accompanied by the sensitisation of the cis→trans (but not of the trans→cis) isomerisation. The rate constant of the thermal cis→trans isomerisation of the azobenzene units has also been measured. Comparison of the results obtained for model compounds and for the G4 dendrimer shows that the dendritic structure favours the trans configuration of the azobenzene units (“dendritic effect”), presumably because it is less demanding in terms of space and causes less crowding on the dendrimer surface. © 2002 The Royal Society of Chemistry and Owner Societies
Effect of protons and metal ions on the fluorescence properties of a polylysin dendrimer containing twenty four dansyl units
No full textThe interaction of protons, Co2+, Ni2+ and Zn2+ ions (as nitrate salts) with a polylysin dendrimer, D, functionalized in the periphery with 24 5-dimethylamino-l-naphthalenesulfonamido (dansyl) units has been investigated in acetonitrile-dichloromethane solution. The dendrimer consists of a benzene core branched in the 1, 3, and 5 positions. Each branch starts with a (dialkyl)carboxamide-type moiety and carries (i) six aliphatic amide groups and (ii) eight fluorescent dansyl units. For comparison purposes, the behaviour of a monodansyl reference compound (I) has also been investigated. The absorption spectrum and the fluorescence properties of the dendrimer are those expected for a species containing 24 non-interacting dansyl units. Both for the model compound and for the dendrimer, protonation causes a shift of the absorption and fluorescence bands towards higher energies; for the dendrimer, however, the changes in fluorescence intensity during the acid titration reveal the occurrence of intradendrimer quenching processes, with signal amplification. Addition of Co2 or Ni2+ ions to a basic solution of the model compound I does not cause any effect in the absorption and emission properties, whereas in the case of dendrimer D a strong fluorescence quenching is observed. At low metal ion concentration each metal ion quenches about 9 dansyl units; the fluorescence quenching takes place by a static mechanism involving co-ordination of metal ions in the interior of the dendrimer. Addition of Zn2+ to a basic solution of the dendrimer causes only a very small decrease in the fluorescence intensity. The co-ordinated Co2+ and Ni2+ ions are fully displaced by addition of Zn2 or H"1" with revival of the dansyl fluorescence. The results obtained show that a dendrimer can exhibit an unusual co-ordinating ability and sensory signal amplification. © The Royal Society of Chemistry 2000
Photochemical, photophysical and electrochemical properties of six dansyl-based dyads
No full textWe have prepared six dyads containing a fluorescent propyldansylamide (PD) unit covalently linked to nitrobenzene (NB), naphthalene (NA), trans- and cis-azobenzene (tAZ and cAZ), 2,2′-bipyridine (BPY), and [Ru(bpy)3]2+ (RU) moieties. The photochemical, photophysical, and electrochemical properties of the dyads have been investigated in acetonitrile solution. In the PD-NB dyad, the fluorescence of the PD unit is quenched by electron transfer to the NB unit at 298 K, but it is not quenched in a rigid matrix at 77 K. In the PD-NA dyad, the fluorescence of the naphthalene unit is completely quenched by competing energy (80% efficiency) and electron transfer processes. In the case of PD-tAZ, the dansyl fluorescence is quenched without sensitization of the trans → cis photoisomerization reaction of the tAZ moiety, whereas in the PD-cAZ dyad the dansyl fluorescence quenching is accompanied by the sensitisation of the cis → trans photoisomerization of the cAZ moiety. In the PD-BPY dyad the fluorescence of the dansyl moiety is sensitized by the BPY unit; upon protonation or Zn2+ complexation of the BPY unit, however, the dansyl fluorescence is quenched by electron transfer. In the PD-RU dyad, the fluorescence of the dansyl unit is quenched by competing energy (25% efficiency) and electron transfer processes, whereas the emission of the RU moiety is unaffected
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