Spectroscopic Manifestation of a Weak van der Waals Interaction Between trans-Stilbene and Hexagonal Boron Nitride Surface

Abstract

The interaction between organic molecules and nanomaterials leads to complexation or the functionalization of later and modification of their properties, which are promising for electronics, terahertz technology, photonics, medical imaging, drug delivery, and other applications. Based on theoretical and experimental (THz, Raman, and fluorescence spectroscopy) studies, we analyzed the main spectroscopic characteristics of a weakly bound van der Waals complex of trans-stilbene (TS) molecule and hexagonal boron nitride (hBN). Raman scattering was demonstrated to be the most effective tool to confirm complex formation, exhibiting blue-shifted TS fingerprint lines in the TS + hBN Raman spectrum with respect to the spectra of pure TS or BN. These trends were also confirmed by density functional theory calculations. Coherent anti-Stokes Raman scattering microscopy was applied to check the complex structure. The THz absorption spectra demonstrated additional weak bands that can be assigned to the TS librations relative to the hBN surface, thus confirming the formation of the complex. The presence of hBN at the interface of the TS crystals also results in a relative enhancement of the 364 nm TS vibronic band in the TS + hBN fluorescence spectrum as well as faster FL decay kinetics. Based on the calculations performed in two different approaches, we also concluded that dispersion forces are critical for the adsorption of the TS molecules on the hBN surface.