“…[2][3][4][5][6] More recently, a number of experimental studies have focused their attention on polycrystalline and crystalline materials, featuring a more ordered structure and optical properties usually dominated by vibronic progressions. The growth of very ordered samples, up to the very recent creation of anthracene-based single-crystal microcavities, 7,8 has allowed the observation of different phenomena arising from the strong optical anisotropy of organic crystals. [9][10][11][12] On the other side, vibronic replicas have been strongly coupled to light, with the consequent observation of three ͑or more͒ polariton dispersion relations.…”