Optical Absorption and Emission of Two-Dimensional Tetracene Crystals

Organic crystals have received much attention because of their unique properties different from inorganic crystals such as mechanical flexibility and high quantum yield of luminescence. Although various organic solids are used in many industrial applications, the electronic structures of low-dimensional forms are far from being understood not only because their van der Waals interactions between molecules are intractable but also because it has been a challenge to prepare such crystalline systems with sufficient stability. In this work, we present absorption and emission spectroscopy on single and few-layer tetracene (Tc) layers sandwiched between two-dimensional (2D) inorganic crystals including graphene and hexagonal BN. Tc deposited by thermal evaporation formed flat films with thickness of multiples of its minimum (~1.3 nm) and long-range order confirmed by polarized spectroscopy. Vibrational progressions and Davydov splitting observed in the absorption and emission spectra revealed significant deviation from their bulk counterparts, which suggests distinctive crystalline structures and dielectric environments of 2D Tc. We will also discuss structural details and excitonic dynamics probed by time-resolved spectroscopy.