191032-93-6Relevant academic research and scientific papers
Synthesis, photophysical properties, and photovoltaic devices of oligo(p-phenylene vinylene)-fullerene dyads
Peeters, Emiel,Van Hal, Paul A.,Knol, Joop,Brabec, Christoph J.,Sariciftci, N. Serdar,Hummelen,Janssen, Rene A. J.
, p. 10174 - 10190 (2007/10/03)
The synthesis of a homologous series of oligo(p-phenylene vinylene)-fulleropyrrolidines (OPVn-C60, n = 1-4, where n is the number of phenyl rings) is described. The photophysical properties of these donor-acceptor dyads and the corresponding model compounds, α,ω-dimethyl-2,5-bis(2-(S)-methylbutoxy)-1,4-phenylene vinylene oligomers (OPVn, n = 2-4) and N-methylfulleropyrrolidine (MP-C60), are studied as a function of the conjugation length in solvents of different polarity and as thin films. Fast singlet energy transfer occurs after photoexcitation of the OPVn moiety of the dyads toward the fullerene moiety in an apolar solvent. Photoexcitation of the dyads in a polar solvent results in electron transfer for OPV3-C60 and OPV4-C60, and to some extent for OPV2-C60, but not for OPV1-C60. These results are compared to the results obtained for mixtures of OPVn and MP-C60 in the same solvents. The solvent-dependent change in free energy for charge separation of the donor-acceptor systems is calculated from the Weller equation, and the rate constants for energy and electron transfer are derived from the fluorescence lifetime and quenching. The results show that in a polar solvent electron transfer in these dyads is likely to occur via a two-step process, that is, a very fast singlet energy transfer prior to charge separation. In thin solid films of OPV3-C60 and OPV4-C60, a long-lived charge-separated state is formed after photoexcitation. The long lifetime in the film is attributed to the migration of charges to different molecules. A flexible photovoltaic device is prepared from OPV4-C60.
Constitutionally asymmetric and chiral [2]pseudorotaxanes
Asakawa, Masumi,Ashton, Peter R.,Hayes, Wayne,Janssen, Henk M.,Meijer,Menzer, Stephan,Pasini, Dario,Stoddart, J. Fraser,White, Andrew J. P.,Williams, David J.
, p. 920 - 931 (2007/10/03)
The self-assembly and characterization of a range of chiral pseudorotaxanes has been explored using chiroptical methods. The syntheses of (i) constitutionally asymmetric acyclic hydroquinone-containing polyethers and (ii) optically active hydroquinone-containing acyclic polyethers, bearing pairs of methyl or isobutyl groups related to each other in a C2-symmetric manner within the polyether backbone, are described. The combination of (i) the tetracationic cyclophane cyclobis(paraquat-p-phenylene) tetrakis(hexafluorophosphate), possessing a π-electron deficient cavity, and (ii) the linear noncentrosymmetric acyclic polyethers produces [2]pseudorotaxanes that have been characterized by 1H NMR, UV/vis and circular dichroism (CD) spectroscopies in solution and by X-ray crystallography in the solid state. The introduction of constitutional asymmetry or chirality gives rise to a number of different geometries for the [2]pseudorotaxanes in both the solution and solid states. In particular, CD-spectroscopic measurements on the optically active [2]pseudorotaxanes have shown that-depending on the positions of the C2 symmetrically related chiral centers in the polyether chains with respect to the hydroquinone rings - the chirality present in the π-electron rich threadlike guest can induce chirality that is associated with the supramolecular structure as a whole, resulting in a chiral charge-transfer transition involving not only the π-donors in the chiral guests but also the π-acceptors in the achiral host.
