Excitons in a perfect quasi-1D organic quantum wire, an isolated polydiacetylene chain

The exciton in single luminescent polydiacetylene (PDA) chains dispersed in their single crystal monomer matrix is studied. As reported these quantum wires have the properties of a perfect quasi-1D semiconducting system. The macroscopic spatial coherence of a single exciton state on a chain as a function of temperature is investigated using an interference experiment. The interference pattern contrast decreasing with increasing temperature is non zero up to 30 K. Experiments developed in order to observe the regime of formation of the stationary coherent exciton state are described. Within the time resolution of the experiment, it is concluded that the formation of this state is faster than similar to 5 picoseconds which confirms the assumption of a transient regime. Finally the first steps of the manipulation of phase locked excitonic wave-packets on a PDA wire are discussed. The experimental results measured in a weak exciton-photon coupling regime are compared to simulations obtained through the Bloch optical equations in the framework of a three-levels model. A direct estimate of the coherence time of the vibronic state photocreated in the present non resonant scheme is derived. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA. Weinheim