Summary form only given. The rapid advancement in fullerene chemistry allows the covalent functionalization of C/sub 60/ with electron donors. Various C/sub 60/-based donor-acceptor dyads have been synthesized and studied to gain insight in the intramolecular photophysical processes, like energy and electron transfer. Although these dyads can serve as a model compounds for the conjugated photovoltaic cells, only a few examples have been reported with these C/sub 60/-based dyads. Apart from being well-defined model systems for photophysical characterization, the covalent linkage between donor,and acceptor in these molecular arrays provides a simple method to achieve control over the phase segregation in donor-acceptor networks. We investigate an oligo(phenylene vinylene)fullerene dyad with 4 phenyl groups (C/sub 60/-OPV/sub 4/) in solvents of different polarity using femtosecond pump-probe spectroscopy. We find that photoexcitation of the oligomer leads first to an intramolecular energy transfer to the fullerene, while an electron transfer is a secondary process, only allowed in polar solvents.
Summary form only given. In the last few years the interest in organic quantum wells has grown very rapidly due to their potential applications in NLO electronics etc. Aimed at obtaining regularly spaced wells along the polymeric chain axis, we have designed and prepared a novel class of conjugated polymers consisting of regularly alternating low gap thienylenic (T) and high gap phenylenic (B) mojeties of various length corresponding to the general formula (T/sub x/B/sub y/)/sub n/. With the intent of understanding the effects of the presence of energy barriers and the role of interchain transfers on the formation and decay of selftrapped excitations, we have studied the photoexcitation dynamics of these conjugated regular block copolymers by measuring the femtosecond bleaching decay and the photoluminescence picosecond decay of (T/sub 3/B/sub 2/)n and (T/sub 6/B/sub2/)/sub n/ in films, pellets and solutions..While the ferntosecond transient transmission changes are sensistive to the intrachain processes involving the formation of the exciton-polaron, the decay in the picosecond-nanosecond range is controlled by the interchain hopping of the excitons towards recombination sites and is therefore dependent on the sample supermolecular organization. The effect of the presence of the barriers is discussed by comparing the decay behaviour of the copolymer with those of the homopolymer.
We demonstrate single-mode laser emission at 490 nm from a stable cavity based on a methyl-substituted poly-(para-phenylene)-type ladder polymer. The laser emission is characterized by a well-defined excitation fluence threshold, a high directionality, and a drastic spectral narrowing. The laser generates picosecond pulses of excellent amplitude stability.
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