Enhanced Exciton Delocalization in Exfoliated 2D Tetracene Molecular Crystals

Two-dimensional (2D) crystalline molecular solids exhibiting strong optical transitions provide a promising platform for exploring fundamental photophysical phenomena such as singlet exciton fission, superradiance, and Frenkel–charge-transfer exciton coupling [1]. Dimensional reduction in these systems induces dielectric de-screening, which modifies both their electronic and geometric structures, thereby enabling the design of novel optical functionalities. In this work, we demonstrate the mechanical exfoliation of 2D tetracene crystals down to a few layers and reveal their distinctive excitonic behavior in the 2D limit. Using electron diffraction, we compare their crystal structure with that of 2D tetracene crystals grown by physical vapor deposition [2]. As the thickness decreases, we observe a reduction in Davydov splitting of the lowest exciton states, diminished vibrational progression, and an enhanced Stokes shift—indicating increased exciton delocalization in the 2D regime. These findings shed new light on exciton behavior in 2D molecular systems and open avenues for designing materials and devices with tailored photophysical properties.



References

[1] D. Kim, S. Lee, J. Park, J. Lee, H. C. Choi, K. Kim and S. Ryu,* “In-Plane and Out-of-Plane Excitonic Coupling in 2D Molecular Crystals”, Nature Commun. 14, 2736 (2023).

[2] S. Koo, I. Park, K. Watanabe, T. Taniguchi, J. Shim and S. Ryu,* “Extraordinary Photostability and Davydov Splitting in BN-Sandwiched Single-Layer Tetracene Molecular Crystals”, Nano Lett. 21, 6600 (2021).