A Model Oligomer Approach to Light-Emitting Semiconducting Polymers

Molecular engineering of C60-based conjugated oligomer ensembles: modulating the competition between photoinduced energy and electron transfer processes

A series of novel and soluble C60-(pi-conjugated oligomer) dyads were synthesized, starting from suitably functionalized oligomer precursors (i.e., dihexyloxynaphthalene, dihexyloxynaphthalene-thiophene, and dihexyloxybenzene-thiophene). A systematic change in the nature of the oligomeric component allowed (i) tailoring the light absorption of the chromophore by shifting the ground-state absorption from the ultraviolet to the visible region and (ii) varying the oxidation potential of the donor. The resulting electro- and photoactive dyads were examined by electrochemical and photophysical means. In general, both singlet-singlet energy transfer and intramolecular electron transfer were found to take place and, most importantly, to compete with each other in the overall deactivation of the photoexcited oligomer. The selection of polar solvents in combination with the dihexyloxybenzene-thiophene donor shifted the reactivity from an all energy (1a; dihexyloxynaphthalene) to an all electron-transfer scenario (1d, dihexyloxybenzene-thiophene). Encouraged by the favorable electron-transfer properties of dyad 1d, we prepared photodiodes by embedding 1d between asymmetric metal contacts, which showed external monochromatic efficiencies (IPCE) close to 10% at the maximum absorption of the molecule.

A Synthetic Strategy Leading to Monodisperse PPV Oligomers by Coupling Reactions of Vinyltrimethylsilanes

A novel strategy for the synthesis of well-defined oligo(phenylenevinylene)s was developed. The procedure is entirely based upon two coupling processes, both involving vinyltrimethylsilanes. Bis(styryl)benzenes 2a-g bearing two octyloxy groups in the central aromatic ring and various substituents on the external aromatic rings were prepared in good yield by a regio- and stereoselective coupling reaction of 1 with different arenediazonium tetrafluoroborates. Oligomers with a more extended conjugated system, 4a-c, and with m-phenylene subunits 13a,b, were also readily obtained by conversion of the unsaturated trimethylsilyl derivatives 3a,c,d to the corresponding boron derivatives and a subsequent coupling reaction with compounds 2a and 2c.