It is well established that bringing a plasmonic tip into the proximity of a single molecule inevitably affects its state and vice versa. Due to the enhanced light–matter interaction, spectroscopic information on the molecule captured with tip‐enhanced Raman spectroscopy (TERS) can noticeably differ on that coming from standard far‐field Raman spectroscopy. In this work, we develop a theoretical approach for calculating Raman tensors of a single oblate molecule that takes near‐field depolarization effects into account. Generally speaking, a tip‐dressed molecule exhibits the modified polarizability and, therefore, the Raman tensors. It is reported that the TERS technique can be used to reconstruct Raman tensors of vibration modes of anisotropic single molecules. The symmetric and antisymmetric modes of the molecules nearby a plasmonic tip are enhanced differently. In order to unravel the Raman tensors, two near‐field depolarization factors are necessarily introduced for the oblate molecule. As an example, we consider a free base porphine molecule as a test molecule to demonstrate the enhancement of intensities of Raman bands assigned to different symmetries. Also, we demonstrate an experimental way how to measure the depolarization factors using an ensemble of randomly oriented molecules. We believe that our finding will be beneficial to the interpretation of TERS measurements of single molecules.

中文翻译：

---

尖端修饰的卟啉分子拉曼张量

众所周知，将等离激元尖端带到单个分子附近不可避免地会影响其状态，反之亦然。由于光-物质相互作用的增强，用尖端增强拉曼光谱（TERS）捕获的分子的光谱信息可能与标准远场拉曼光谱的信息明显不同。在这项工作中，我们开发了一种理论方法来计算单个扁形分子的拉曼张量，其中考虑了近场去极化效应。一般而言，尖端修饰的分子具有改进的极化率，因此具有拉曼张量。据报道，TERS技术可用于重建各向异性单分子振动模式的拉曼张量。等离激元尖端附近的分子的对称和反对称模式得到不同地增强。为了解开拉曼张量，必须为扁圆形分子引入两个近场去极化因子。例如，我们考虑将游离碱卟啉分子作为测试分子，以证明分配给不同对称性的拉曼谱带强度增强。此外，我们演示了一种实验方法，该方法如何使用一组随机定向的分子来测量去极化因子。我们相信，我们的发现将有利于单分子TERS测量的解释。我们考虑将游离碱卟啉分子作为测试分子，以证明分配给不同对称性的拉曼谱带强度增强。此外，我们演示了一种实验方法，该方法如何使用一组随机定向的分子来测量去极化因子。我们相信，我们的发现将有利于单分子TERS测量的解释。我们考虑将游离碱卟啉分子作为测试分子，以证明分配给不同对称性的拉曼谱带强度增强。此外，我们演示了一种实验方法，该方法如何使用一组随机定向的分子来测量去极化因子。我们相信，我们的发现将有利于单分子TERS测量的解释。