Mechanisms for Fluorescence Depolarization in Dendrimers

Vicinelli, Veronica; Bergamini, Giacomo; Ceroni, Paola; Balzani, Vincenzo; Vögtle, Fritz; Lukin, Oleg

doi:10.1021/jp070468p

Cited by 18 publications

(13 citation statements)

References 52 publications

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“…The hydrodynamic radius of 1.6 nm obtained for G4 compares nicely to the radius of gyration of 1.5 nm obtained from the simulation ( Figure 11). Our results are in accord with previous theoretical and experimental studies 11,12,37 for POPAM dendrimers, and the hydrodynamic volumes are comparable to the volumes of 5.8, 12.6, and 17.4 nm 3 for G2, G3, and G4, respectively, in dichloromethane determined by Vicinelli et al 69 Besides vanishing by overall rotation, fluorescence anisotropy may disappear due to motions of individual dansyls as well as due to excitation energy transfer (EET) between dansyls. In the higher-generation dendrimers, EET is more likely to become an important dansyl-dansyl relaxation channel than in the smaller ones.…”

Section: Discussionsupporting

confidence: 93%

Internal Dynamics and Energy Transfer in Dansylated POPAM Dendrimers and Their Eosin Complexes

et al. 2010

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Internal dynamics of dansylated poly(propyleneamine) dendrimers (POPAM, G1-G4) in solution and excitation energy transfer from dansyls to eosin in POPAM-eosin complexes have been studied by time-resolved fluorescence spectroscopy and molecular dynamics (MD) simulations. Combining the results from fluorescence anisotropy and the MD simulation studies suggests three time domains for the internal dynamics of the G3 and G4 generations, about 60 ps for motions of the outer-sphere dansyls, 500-1000 ps for restricted motions of back-folded dansyls, and 1500-2600 ps for the overall rotation. For the smaller generations, the contribution from the restricted motions was not entirely evident. Eosin binding hinders fast rotation of the dansyl fragments in the largest G4 dendrimer, but the motion of back-folded dansyls is more hindered in the pure dendrimer. Both fluorescence anisotropy and MD results for the G4 dendrimer support the "soft" dendrimer picture with almost free mobility and substantial back-folding of the dansyls of the dendrimers in solution. Analysis of time-dependent spectral shifts of fluorescence reveals 20-30 ps excited-state solvation relaxation around a single dansyl of a dendrimer. Dendrimer-independent excitation energy transfer from 4 to 8 ps from dansyls to eosins in POPAM-eosin complexes G2-G4 was observed.

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Section: Discussionsupporting

confidence: 93%

Internal Dynamics and Energy Transfer in Dansylated POPAM Dendrimers and Their Eosin Complexes

et al. 2010

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“…At 25% fluorophore substitution, fluorescence was weaker because less fluorophore was present, and at 75% fluorophore substitution fluorescence was weaker because the fluorophores were packed closely enough for some degree of self‐quenching. In a study of the mechanism of fluorescence depolarization of PPI dendrimers with 1,5‐D fluorophore on the periphery, the predominant mechanism was found to be local motion and intrinsic deactivation of the fluorophore, with no evidence for energy migration between fluorophores (probably because of the large Stokes shift between absorption maximum and emission maximum of D units) 15…”

Section: Resultsmentioning

confidence: 99%

“…In a study of the mechanism of fluorescence depolarization of PPI dendrimers with 1,5-D fluorophore on the periphery, the predominant mechanism was found to be local motion and intrinsic deactivation of the fluorophore, with no evidence for energy migration between fluorophores (probably because of the large Stokes shift between absorption maximum and emission maximum of D units). 15 Since G2(D) 8 (DMOMS) 8 compositions gave robust and strongly fluorescent coatings after cure, glass microscope slides (coupons) carrying these coatings were studied by fluorescence spectroscopy. The data showed that changing from an amino to a DMOMS environment had little effect upon the 1,5-D and 2,5-D fluorescence emission wavelengths, which remained at 507 nm and at 490 nm, respectively.…”

Section: Fluorescent Nanostructured Coatingsmentioning

confidence: 99%

“…44 The 1,5-dansyl fluorophore can either exist with the dimethylamino and naphthyl moieties in coplanar conformation in the excited state (k em $430 nm), or in twisted conformation in the excited state (k em $500 nm). 51 The coplanar conformation is favored in hydrophobic or nonpolar environments, while the twisted conformation is favored in hydrophilic or polar environments, and 4 506 528 549 G0 (1,5-D) 2 (NH 2 ) 2 511 532 544 G1 (1,5-D) 8 507 530 544 G1 (1,5-D) 4 (NH 2 ) 4 506 528 541 G2 (1,5-D) 16 505 529 533 G2 (1,5-D) 15 (NH 2 ) 506 528 534 G2 (1,5-D) 14 (NH 2 ) 2 506 528 534 G2 (1,5-D) 13 (NH 2 ) 3 506 527 534 G2 (1,5-D) 12 (NH 2 ) 4 506 535 533 G2 (1,5-D) 11 (NH 2 ) 5 506 530 533 G2 (1,5-D) 10 (NH 2 ) 6 506 530 533 G2 (1,5-D) 8 (NH 2 ) 8 507 531 535 G2 (1,5-D) 4 (NH 2 ) 12 507 527 531 G2 (1,5-D) 2 (NH 2 ) 14 506 527 533 G3 (1,5-D) 32 505 529 533 G3 (1,5-D) 24 (NH 2 ) 8 504 535 533 G3 (1,5-D) 16 (NH 2 ) 16 506 530 535 G3 (1,5-D) 8 (NH 2 ) 24 508 528 531 G4 (1,5-D) 32 (NH 2 ) 32 528 535 536 G2 (2,5-D) 16 488 495 495 G2 (2,5-D) 12 (NH 2 ) 4 487 495 495 G2 (2,5-D) 8 (NH 2 ) 8 488 493 496 G2 (2,5-D) 4 (NH 2 ) 12 488 495 494 HB-PU, 100% 1,5-D 507 NA 536 HB-PU, 75% 1,5-D 513 NA 537 HB-PU, 50% 1,5-D 511 NA 536 HB-PU, 25% 1,5-D 505 NA 532 16 514 540 543 G2 (NBD) 12 (NH 2 ) 4 523 539 543 G2 (NBD) 8 (NH 2 ) 8 525 546 551 G2 (NBD) 4 (NH 2 )...…”

Section: Effect Of End-group Substitution Generation and Type Of Dementioning

confidence: 99%

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Fluorescent dendritic polymers and nanostructured coatings for the detection of chemical warfare agents and other analytes

Hartmann-Thompson

Keeley

Rousseau

et al. 2009

J. Polym. Sci. A Polym. Chem.

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Polyamidoamine (PAMAM) dendrimers of generations zero (G0) to four (G4), and a hyperbranched polyurea (HB‐PU), were functionalized with 1,5‐dansyl (1,5‐D), 2,5‐dansyl (2,5‐D), 2,6‐dansyl (2,6‐D) and nitrobenzofurazan (NBD) fluorophores that change their fluorescence emission wavelength in response to chemical environment, and the resulting dendritic polymers were characterized by MALDI‐TOF mass spectrometry, 1H NMR, 13C NMR, and fluorescence spectroscopy. Fluorophore‐functionalized dendritic polymers were then reacted further with 3‐acryloxypropyldimethoxymethylsilane (AOP‐DMOMS) at various fluorophore to DMOMS substitution ratios. The resulting materials were cast onto glass slides, and cured into robust nanostructured coatings. Coatings with 50% fluorophore–50% DMOMS substitution showed the strongest fluorescence and the best physical properties. Coated coupons were tested against a wide range of analytes including the chemical warfare agent simulants dimethyl methylphosphonate (DMMP) and chloroethylethylsulfide (CEES), and the water‐methanol‐ethanol series. It was found that the ability of the coatings to distinguish between analytes decreased with increasing cross‐link density for both dendrimer and hyperbranched polymer‐based coatings. It was also found that the percent fluorophore substitution and the type of dendritic polymer carrying the fluorophore had no significant effect upon fluorescence emission wavelength, but fluorescence emission wavelength became less dependent upon solvent with increasing dendrimer generation and molecular mass. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5101–5115, 2009

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“…As previously discussed, [12] fluorescent depolarization can occur in a dendrimer by three distinct mechanisms depending on the nature, position, and number of fluorescent units contained in the dendritic structure: 1) local motion of the fluorophore; 2) global rotation of the dendrimer; 3) energy migration among fluorophores. For the compounds studied here depolarization channels related to intramolecular energy migration are not available because the pentaphenylene core is the unique fluorescent component.…”

Section: Fluorescence Anisotropymentioning

confidence: 97%

Dendrimers with a Pentaphenylene Core: A Photophysical Study

Bergamini¹,

Ceroni²,

Balzani³

et al. 2009

ChemPhysChem

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Novel dendrimers G2PC and G4PC consisting of a p-pentaphenylene core (PC) appended in the para position with two second-generation (G2) or two fourth-generation (G4) sulfonimide branches and two n-octyl chains, as well as a model compound of the pentaphenylene core (G0PC), are prepared. The photophysical properties (absorption, emission, and excitation spectra; fluorescence decay lifetime; and fluorescence anisotropy spectra) of the three compounds are investigated under different experimental conditions (dichloromethane solution and solid state at 293 K, dichloromethane/methanol rigid matrix at 77 K). In the absorption spectra contributions from both the branches and the core can be clearly identified. The fluorescence spectra show only the characteristic fluorescence of the pentaphenylene unit with lambda(max) around 410 nm in fluid solution and 420 nm in the solid state. In solution the fluorescence quantum yields are 0.78, 0.76, and 0.72 for G0PC, G2PC, and G4PC, respectively, and the fluorescence lifetime is about 0.7 ns in all cases. Energy transfer from the chromophoric groups of the dendrimer branches to the core does not occur. The three compounds show the same, high steady-state anisotropy value (0.35) in dilute rigid-matrix solution at 77 K. In dichloromethane at 293 K, the increasing anisotropy values along the series G0PC (0.17), G2PC (0.27), and G4PC (0.32), with increasing molecular volume of the three compounds, show that depolarization takes place by molecular rotation. In the solid state the anisotropy is very low (0.015, 0.017, and 0.035 for G0PC, G2PC, and G4PC, respectively), probably because of fast depolarization via energy migration.

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Mechanisms for Fluorescence Depolarization in Dendrimers

Cited by 18 publications

References 52 publications

Internal Dynamics and Energy Transfer in Dansylated POPAM Dendrimers and Their Eosin Complexes

Internal Dynamics and Energy Transfer in Dansylated POPAM Dendrimers and Their Eosin Complexes

Fluorescent dendritic polymers and nanostructured coatings for the detection of chemical warfare agents and other analytes

Dendrimers with a Pentaphenylene Core: A Photophysical Study

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