发表机构
Pohang University of Science and Technology (POSTECH); Hanyang University; Research Institute of Natural Science, Hanyang University; Yonsei University; National Institute for Materials Science; Queens College, City University of New York; Graduate Center, City University of New York（浦项科技大学; 汉阳大学; 汉阳大学自然科学研究院; 延世大学; 物质材料研究机构; 纽约市立大学皇后学院; 纽约市立大学研究生院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过机械剥离获得单层至少层的并四苯等分子晶体，发现厚度减小导致Davydov劈裂减弱、斯托克斯位移增大及激子离域增强，实现了分子晶体激子性质的维度调控。
AI 中文摘要
二维（2D）材料通过降低维度、改变介电屏蔽和依赖层数的结构重构，为调控激发态性质提供了独特机遇。尽管这些效应已在无机体系中得到广泛探索，但在分子晶体中，由于难以在保持晶体有序性的同时实现原子尺度的厚度控制，其实现一直受限。在此，我们展示了并四苯及其他三种分子晶体可被机械剥离成单层、少层或多层薄片，同时保持晶体有序性。这一能力使得在相同结构组织内、明确界定的厚度范围内对分子晶体进行新研究成为可能。这些样品的厚度依赖光谱揭示了面外限域如何改变并四苯的激发态能量景观：随着厚度减小，Davydov劈裂减弱，斯托克斯位移增大，并出现更离域激子的特征。电子衍射和基于激子模型的分析将这些趋势与分子堆积、分子间耦合及介电屏蔽的变化相关联。我们的结果还表明，分子激子的关键特征可通过层数系统调控，将维度控制从无机二维材料扩展到分子晶体。
英文摘要
Two-dimensional (2D) materials provide unique opportunities to tailor excited-state properties through reduced dimensionality, altered dielectric screening and layer-dependent structural reconstruction. While such effects have been widely explored in norganic systems, their realization in molecular crystals has been limited by the difficulty of controlling thickness at the atomic scale while preserving crystalline order. Here we show that tetracene and three other molecular crystals can be mechanically exfoliated into mono-, few- or multilayer flakes, while retaining crystalline order. This capability enables new studies of molecular crystals across a well defined thickness range within the same structural organization. Thickness-dependent spectra of these samples reveal how out-of-plane confinement modifies the excited-state energy landscape of tetracene: With decreasing thickness, the Davydov splitting diminishes, the Stokes shift increases, and signatures of more delocalized excitons emerge. Electron diffraction and exciton model-based analyses correlate these trends to changes in molecular packing, intermolecular coupling and dielectric screening. Our results also demonstrate that key features of molecular excitons can be systematically tuned by layer number, extending dimensional control from inorganic 2D materials to molecular crystals.
