Monodisperse fluorene oligomers exhibiting strong dipolar coupling interactions.
Laboratoire de Stéréochimie et Interactions Moléculaires, ENS-Lyon and CNRS, 46 Allée d'Italie, 69364 Lyon, France.Chemical Communications (Impact Factor: 6.38). 09/2002; DOI:10.1039/B201414A
ABSTRACT Well-defined fluorene oligomers (n = 1 to 6) were prepared step by step using Suzuki and Yamamoto couplings, while absorption and photoluminescence properties evidenced very large dipolar coupling interactions between fluorene moieties.
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ABSTRACT: The excited-state dynamics of a series of four poly[2,7-(9,9-bis(2-ethylhexyl)fluorene] fractions, PF2/6, with different chain length (degrees of polymerization DP: 5, 10, 39 and 205) was investigated in dilute solutions by steady-state and time-resolved fluorescence techniques. Two decay components are extracted from time-resolved fluorescence experiments in the picosecond time domain: a chain length dependent, fast decay time (τ2) for shorter emission wavelengths (ranging from 30 to 41 ps), that is associated to a rising component at longer wavelengths, and a longer decay time, τ1, (ranging from 387 to 452 ps). The system was investigated with kinetic formalisms involving: (i) a two-state system (A and B) involving conformational relaxation of the initially excited PF2/6 segment (A) under formation of a more planar (B), relaxed state and (ii) considering a time-dependent red-shift of the emission spectrum using the Stokes shift correlation function (SSCF). In the case of (i), the kinetic scheme was solved considering the simultaneous excitation of A and B, or only of A and the rate constants for formation [k'CR or k'CR(α)], dissociation (k-CR) and deactivation (k*B), were obtained together with the fraction of species A and B present in the ground-state. The use of the SSCF, (ii), was found more adequate leading to a decay law with a 3.4 ps component (associated to the slow part of the solvation dynamics process) and a longer decay (43.3 ps) associated to the conformational/torsional relaxation process with an associated rate constant, kCR. This longer component of the SSCF was found identical to the short-living decay (τ2) component of the bi-exponential decays displaying an Arrhenius-type behavior with activation energy values in the range of 5.8-8.9 kJ mol-1 in toluene and 6.5-10.7 kJ mol-1 in decalin. From the dependence of the fast decay component (kCR≡1/τ2) on solvent viscosity and temperature, the activation energy for the conformational relaxation process was found to be distinctly dependent on the chain length, with the relaxation rate dependence with the solvent viscosity (kCR~η- γ) displaying γ=1 for the oligomer fraction with DP=5 (i.e., kCR is associated to a pure diffusion-controlled process), and γ<1 for the higher molecular weight PF2/6 fractions (with DP=10, 39, 205). This happens due to a decreased conformational barrier between non-relaxed and relaxed states promoted by the polymer skeleton.The Journal of Physical Chemistry B 05/2013; · 3.61 Impact Factor
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ABSTRACT: Strategies for the design and construction of non-linear, 2D and 3D conjugated macromolecules are presented in this critical review. The materials, termed here as star-shaped structures, feature a core unit which may or may not provide conjugated links between arms that radiate like spokes from a central axle. The arms of the macromolecules consist of linear oligomers or irregular conjugated chains lacking a formal repeat unit. The cores range from simple atoms to single or fused aromatic units and can provide a high level of symmetry to the overall structure. The physical properties of the star-shaped materials can be markedly different to their simple, linear conjugated analogues. These differences are highlighted and we report on anomalies in absorption/emission characteristics, electronic energy levels, thermal properties and morphology of thin films. We provide numerous examples for the application of star-shaped conjugated macromolecules in organic semiconductor devices; a comparison of their device performance with those comprising analogous linear systems provides clear evidence that the star-shaped compounds are an important class of material in organic electronics. Moreover, these structures are monodisperse, well-defined, discrete molecules with 100% synthetic reproducibility, and possess high purity and excellent solubility in common organic solvents. They feature many of the attributes of plastic materials (good film-forming properties, thermal stability, flexibility) and are therefore extremely attractive alternatives to conjugated polymers (210 references).Chemical Society Reviews 07/2010; 39(7):2695-728. · 24.89 Impact Factor
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ABSTRACT: Soluble green light-emitting poly(9,9-dihexylfluorene-co-fluorenone) was synthesized by solvent-free oxidative coupling polymerization of 9,9-dihexylfluorene in a facile one-step reaction. The polymers were characterized by FT-IR, 1H NMR, 13C NMR, UV-Vis and fluorescence spectroscopy. The region-regular structure of the polymer linking at 2, 7′-position on the fluorene moieties was obtained. The FT-IR spectra of the polymers showed fluorenone vibration. The fluorescence spectra of the solid thin film of the polymers displayed green light-emitting, which was emitted from fluorenone moieties produced in the polymerization process.Wuhan University Journal of Natural Sciences 04/2012; 12(2):327-332.
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