Résumé
The excitonic luminescence of an isolated polydiacetylene polymer chain in its monomer matrix is studied by microphotoluminescence. These chains behave as one-dimensional (1D) systems with the expected 1/ square root E density of states between 5 and 50 K. It is also shown that the exciton coherence time is determined by interactions with LA phonons of the surrounding 3D crystal matrix, thus leading to very fast (ps) exciton thermalization within the band. The optical phonons of the chain that are involved in the vibronic transitions are found to have coherence times ranging from 300 to 600 fs