Exfoliated Two-Dimensional Tetracene Molecular Crystals Studied with Polarized Reflectance and Photoluminescence Spectroscopy

2D molecular crystals grown by physical vapor deposition using inorganic 2D crystals as assembly templates have revealed intriguing novel photophysical [1, 2] and electrical [3] properties. In this work [4], we report on a mechanical exfoliation, a top-down approach, to form 2D crystals of various polyaromatic molecules. This approach, compared to the conventional bottom-up method, can offer advantages in structural quality and thickness control besides less limitation on supporting substrates. We evaluated both methods by quantifying the crystallinity of 2D Tc crystals using wide-field photoluminescence (PL) imaging. Polarimetric analysis, based on two orthogonal polarization components, revealed long-range order that spanned more than several microns. Polarized absorption and PL measurements also showed thickness-dependent Davydov splitting, which can be attributed to varying crystalline structures and mixing of Frenkel and charge transfer exciton states [5]. This study demonstrates that mechanical exfoliation can be applied to various molecular systems to generate their 2D crystal forms, potentially leading to new findings and applications.