Coherent excitonic emission in molecular semiconductors

Coherent excitonic emission in solid-state oligothiophenes is presented and discussed. It is demonstrated that, even in the herringbone type of aggregation, oligothiophenes, with an even number of rings, exhibit superradiant behavior in crystals possessing a high degree of order. The dependence of the bandwidth and the natural (radiative) lifetime on temperature have been measured and related to the number of coherently coupled molecular dipoles. The experimental data are quantitatively interpreted in terms of a recently developed theoretical model for the pinwheel aggregates.