Abstract : This PhD. Thesis is aimed at the investigation of organic nanomaterials presenting original photophysical properties. We address the consequences of the nanostructuration on the absorbing and emissive properties of poly(p-phenylene vinylene) (PPV), a prototype of a semiconducting conjugated polymer for light emitting diode applications. On one hand, we investigate quasi-two dimensional thin composite films of PPV loaded with carbon nanotubes (CNT). On the other hand, we achieve the synthesis of quasi-one dimensional PPV nanofibers exhibiting optical properties different from those of the bulk, which are possibly related to a near confinement regime of the photoexcited species. The PPV/NTC nanocomposite thin films are prepared by drop casting for several concentrations of the PPV precursor polymer and for increasing CNT loads. The optical properties are strongly modified by these synthesis conditions. The interacting effects between polymer chains and CNT on the photoluminescence properties are discussed. The PPV nanofibers are elaborated by the wetting template method in nanoporous membranes. Depending on the synthesis conditions, we obtain either nanowires or nanotubes. These objects present different emissive characteristics. In PPV nanotubes, the quantum yield is increased and a new long-lived photoluminescence band is observed around 450 nm. We discuss the experimental results with two theoretical approaches : (i) molecular calculations of oligomers in order to find the most probable optical transition energies in short chains ; (ii) a phenomenological model based on the distribution of conjugated segment lengths, allowing a better understanding of both intrachain and interchain interactions.