Coherent control of quinquethiophene photoluminescence

Coherent control of molecular properties has become a major topic in the last years. We demonstrate, in a conjugated pentamer of thiophene, that a pair of properly time separated visible pulses can resonantly control the photoluminescence molecular quantum yield. In our experiment coherent control takes place by manipulation of the torsional dynamics through the coupled electronic transition. The molecule under investigation is a functionalized quinquethiophene (T₅AO₂). It belongs to a broad class of thiophene based organic semiconductors which are being considered for a variety of optoelectronics and bio-photonics applications. Optical excitation of T₅AO₂ leads to pi-electron density redistribution, with hardening of the inter-ring bonds. Stiff planar molecules are expected to have larger PL quantum yield with respect to the non planar conformers.