Optical response and emission waveguiding in rubrene crystals

The optical response of rubrene crystals is described by providing the full UV-VIS dielectric tensor. Consistently with the molecular and crystal symmetries, the lowest crystal transition originates from an Au molecular transition, it is polarized along the c axis (normal to the larger crystal face), and it is the origin of the emission, which is self-guided towards the edge where the corresponding polarization and intensity angular distribution are detected. By contrast, the Bu molecular transitions give rise to Davydov states described by the other two components of the diagonal dielectric tensor.