Internal Dynamics of Dendritic Molecules Probed by Pyrene Excimer Formation

Interaction of cyclodextrins with pyrene-modified polyacrylamide in a mixed solvent of water and dimethyl sulfoxide as studied by steady-state fluorescence

The interaction of β- and γ-cyclodextrins (β-CD and γ-CD, respectively) with polyacrylamide modified with pyrenyl (Py) residues (pAAmPy) was investigated in a mixed solvent of water and dimethyl sulfoxide (DMSO) by steady-state fluorescence. In the absence of CD, the fluorescence spectra indicated that the formation of Py dimers became less favorable with increasing volume fraction of DMSO (x(DMSO)). The fluorescence spectra at varying x(DMSO) and CD concentrations indicated that β-CD and γ-CD included monomeric and dimeric Py residues, respectively. Using the fluorescence spectra, equilibrium constants of the formation of Py dimers and the complexation of β-CD and γ-CD with Py residues were roughly estimated based on simplified equilibrium schemes.

Selective multicolour imaging of zebrafish muscle fibres by using fluorescent organic nanoparticles

Glowing fish: Fluorescent organic nanoparticles (FONs) were prepared from pyrene-containing guanine analogues. FONs are able to penetrate into human cells and zebrafish embryos; they are nontoxic, biocompatible and were found to be specific for muscular tissues. This study demonstrates for the first time the possibility of using FONs for in vivo, whole-body, fluorescence imaging of zebrafish.

Synthesis and characterization of novel pyrene-dendronized porphyrins exhibiting efficient fluorescence resonance energy transfer: optical and photophysical properties

A novel series of pyrene dendronized porphyrins bearing two and four pyrenyl groups (Py(2)-TMEG1 and Py(4)-TMEG2) were successfully synthesized. First and second generation Fréchet type dendrons (Py(2)-G1OH and Py(4)-G2OH) were prepared from 1-pyrenylbutanol and 3,5-dihydroxybenzyl alcohol. These compounds were further linked to a trimesitylphenylporphyrin containing a butyric acid spacer via an esterification reaction to obtain the desired products. Dendrons and dendronized porphyrins were fully characterized by FTIR and (1)H NMR spectroscopy and their molecular weights were determined by matrix-assisted laser desorption ionization time of flight mass spectrometry. Their optical and photophysical properties were studied by absorption and fluorescence spectroscopies. The formation of dynamic excimers was detected in the pyrene-labeled dendrons, with more excimer being produced in the higher generation dendron. The fluorescence spectra of the pyrene dendronized porphyrins exhibited a significant decrease in the amount of pyrene monomer and excimer emission, jointly with the appearance of a new emission band at 661 nm characteristic of porphyrin emission, an indication that fluorescence resonance energy transfer (FRET) occurred from one of the excited pyrene species to the porphyrin. The FRET efficiency was found to be almost quantitative ranging between 97% and 99% depending on the construct. Model Free analysis of the fluorescence decays acquired with the pyrene monomer, excimer, and porphyrin core established that only residual pyrene excimer formation in the dendrons could occur before FRET from the excited pyrene monomer to the ground-state porphyrin core.

Unexpected absorbance enhancement upon clustering dyes in a polymer matrix

PE films grafted with poly(methyl acrylate) and labeled with pyrene groups were obtained by irradiation with γ-rays in the presence of acryloyl chloride and further reacting them with 1-pyrenebutanol or 1-pyrenemethylamine. Characterization of the polymer films benefited from the dual use of the pyrene probe as an indicator of, first, polymer chain dynamics by monitoring pyrene excimer formation by fluorescence and, second, polymer morphology by staining the pyrene-rich domains of the films with RuO(4) for scanning electron microscopy (SEM). The grafted polymers labeled with 1-pyrenemethylamine showed much stronger absorbance than those labeled with 1-pyrenebutanol despite having similar pyrene contents. The fluorescence spectra of the grafted polymers labeled with 1-pyrenebutanol exhibited monomer emission, whereas those labeled with 1-pyrenemethylamine exhibited exclusively excimer emission. These dramatic differences could be accounted for by noting that labeling of the grafted poly(acryloyl chloride) with 1-pyrenemethylamine results in cross-linking of the polymer matrix, with an associated enhancement of the concentration of pyrene in the cross-linked domains, which was confirmed by SEM. Formation of discrete domains in the polymer film can induce multiple scattering at the domain boundaries which lengthens the path of light in the film and increases absorption of the light by the tightly packed pyrene-rich domains. Implementation of this effect for fabrication of plastic color filters should generate more efficient filters which should find numerous practical applications.

New insights in the study of pyrene excimer fluorescence to characterize macromolecules and their supramolecular assemblies in solution

This report highlights some of the recent developments that have been made in the quantitative analysis of fluorescence decays acquired with pyrene-labeled macromolecules. With these new analytical tools, macromolecules of different composition and architecture can now be labeled in a variety of ways with the pyrene chromophore, and the kinetics of pyrene excimer formation can be described to retrieve quantitative information about the internal dynamics of the macromolecules studied. In particular, this review presents the procedure that was followed to develop these new analytical tools and how the process of pyrene excimer formation with vinyl polymers, poly(L-glutamic acid), dendrimers, associative polymers, surfactants, and lipids labeled with pyrene has been successfully characterized thanks to these analysis programs.