Dynamics in Small Con ning Systems VI Chairs

Applied Physics Letters, 2000

The excited state relaxation processes of a nitrogen-cored distyrylbenzene-stilbene ͑A-DSB͒ dendrimers and the analogous linear model compound ͑bis-MSB͒ were investigated by polarized fluorescence upconversion spectroscopy. The fluorescence anisotropy ͑FA͒ of A-DSB was found to decay to a value close to zero in less than 200 fs after excitation. For the model compound bis-MSB the FA initial value was close to 0.4 and showed a relatively slow decay ͑82 ps͒ corresponding to the overall rotational diffusion of the molecule. The results are interpreted in terms of fast transition dipole reorientation during relaxation of the excited states of the branched molecules.

ChemPhysChem, 2001

Journal of the American Chemical Society, 2000

Individual multichromophoric dendrimer molecules, bearing eight perylenecarboximide chromophores at the rim, immobilized in a thin polyvinylbutyral (PVB) film were studied by far-field fluorescence microscopy. Fluorescence intensity trajectories as a function of time (transients), spectra, and decay traces were recorded separately or simultaneously. For comparison, similar measurements have been performed on a model compound containing one perylenecarboximide chromophore. Collective on/off jumps of the fluorescence intensity were observed for single dendrimer molecules, resembling previously reported collective jumps for the emission of single light-harvesting antenna systems. Spectra and decays of both non-interacting and dimer-like interacting chromophoric sites could be distinguished within an individual dendrimer. Transitions between the different spectral forms and decay times, observed for a single molecule, underline the dynamic character of the interactions among the chromophores. Evidence for a stepwise bleaching process of the multichromophoric system was found. Furthermore, the single-molecule data incontestably prove the assumptions stated in the ensemble model.

Chemical Physics Letters, 1999

The photophysical properties of a dendrimer 1 bearing eight peryleneimide chromophores on a polyphenylene core were investigated by picosecond fluorescence and femtosecond transient absorption techniques. A peryleneimide attached to Ž . a hexaphenylbenzene unit 2 served as model compound. Multi-exponential fluorescence and fs-transient absorption decays were observed only for 1, which could therefore be attributed to excimer-like interactions among neighbouring peryleneimides. The comparative time-resolved polarisation results on 1 and 2 indicate the occurrence of different depolarisation processes in the dendrimer assignable to the rotation of the molecule, a fractional motion maybe of a dendrimer branch and to an intramolecular energy transfer process. q 1999 Elsevier Science B.V. All rights reserved.

Macromolecules, 2003

The fluorescence of polyphenylene dendrimers and the intramolecular energy transfer in polyphenylene dendrimers containing a perylenediimide core have been investigated in this paper. Polyphenylene dendrimers composed of tens or hundreds of out-of-plane twisted phenyl units exhibit strong fluorescence, with quantum yields ranging from 0.2 to 0.5 depending on the dendrimer generation and its degree of functionality. The fluorescence of polyphenylene dendrimers can be efficiently quenched by the incorporated perylenediimide core, and consequently, a predominant emission from the core has been observed, indicating a very efficient intramolecular energy transfer.

The Journal of Physical Chemistry A, 1997

The quenching of trans-1-(2-anthryl)-2-phenylethene (t-APE) fluorescence by fumaronitrile (FN) was determined as a function of excitation wavelength (λ exc) and temperature (5.0 e T e 80.0°C). Principal component analysis with self-modeling (PCA-SM) was applied separately to the fluorescence spectra at each temperature. Resolved pure conformer fluorescence spectra were based on the condition that Stern-Volmer quenching constants for each conformer be λ exc-independent. A shoulder at the blue edge of the spectra of the more extended, s-trans conformer (t-APE B) becomes more pronounced with increasing temperature revealing fluorescence from a thermally populated S 2 state. Similar, but more subtle changes are evident in the spectra of the s-cis conformer (t-APE A). Both sets of resolved spectra exhibit blue shifts and broadening as the temperature is increased. These spectral changes are reflected in the shape of the eigenvectors obtained from the PCA of each set of spectra and prevent their resolution into S 2 f S 0 and S 1 f S 0 components. An earlier PCA-SM based resolution of a tAPE spectrothermal matrix into S 1 f S 0 fluorescence of tAPE A and S 2 f S 0 , S 1 f S 0 fluorescence spectra of tAPE B is evaluated.

Journal of Luminescence, 1998

Pyrenyl labeled anesiloxane dendrimers and carbosilane hyperbranched polymers have been investigated with the use of various types of fluorescence experiments.

The Journal of Physical Chemistry, 1993

The kinetic behavior of the halato telechelic polymer (N,N-dimethyl-N-[3-(l-pyrenyl)propyl]ammonio)trifluoromethanesulfonate-end-capped poly(tetrahydrofuran) (POLYPROBE) in tetrahydrofuran is investigated by global compartmental analysis of the fluorescence decay surface. At low POLYPROBE concentrations the emission decays monoexponentially. When an analogous end-capped halato telechelic polymer without the pyrene chromophore ((N,N,N-triethylammonio)trifluoromethanesulfonate-end-capped poly(tetrahydrofuran), POLYSALT) is added to solutions containing a low POLYPROBE concentration, the emission can be fitted by a biexponential decay function. From these observations it is concluded that the second excited-state species in the POLYPROBE-POLYSALT system is POLYPROBE involved in ion aggregation due to dipole-dipole or ion-dipole interaction. At higher POLYPROBE concentrations, without added POLYSALT, a triexponential decay function is needed to describe the emission. The third excited-state species is a POLYPROBE excimer, which can be formed via two pathways: either intermolecularly when a locally excited POLYPROBE encounters a ground-state POLYPROBE or intramolecularly when an aggregate of two POLYPROBE molecules rearranges. From the global compartmental analysis in which the value of one of the rate constants is scanned, it is found that the bimolecular processes are slowed down by the presence of the polymer chain, while intramolecular rearrangements are not affected.

Bulletin of the Chemical Society of Japan, 2015

The fluorescence maximum of the fourth generation of stilbene-cored dendrimer (trans-G4) was affected by solvent polarity. These results indicated that the core of even higher generation dendrimer was not isolated from solvent molecules and the environment of the dendrimer core is constructed by both surrounding dendron groups and penetrated solvent molecules.

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.