R-011

Maksim Shundalau

mshundalau@unisa.it

University of Salerno, Italy

Ivan Halimski, Daniil Pashnev, Martynas Talaikis, Andrej Dementjev, Renata Karpicz, Jevgenij Chmeliov, Irmantas Kašalynas, Andžej Urbanovič, Bruno Robert, Patrizia Lamberti

Spectroscopy of van der Waals interaction between organic molecules and hexagonal boron nitride

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. One of the promising materials in this context is hexagonal boron nitride (hBN) nanosheet. The covalent attachment of molecules to the surface or edge of 2D material or quantum dot (QD) allows one to tune its properties robustly. In contrast, non-covalent functionalization of a material provides a way to modify the physical properties using so-called “fine-tuning” without violating its structure. Adsorbed molecules interact with surfaces due to relatively weak van der Waals (vdW) interactions or electrostatic forces. Non-covalent vdW interaction can ensure quite strong adhesion of the molecule to the 2D material or QD surface on the one hand as well as the possibility of its separation without disturbing the structure and loss of target properties on the other. Therefore, for application needs it is important to estimate the magnitude of vdW interaction between hBN and organic materials and its spectroscopic manifestation. Based on experimental (THz, Raman, IR and UV/vis absorption, and fluorescence spectroscopy) and theoretical (DFT calculations) studies we analysed the main spectroscopic characteristics of a weakly bound vdW complexes of hBN and different organic molecules including tetraphenylporphyrin (TPP), trans-stilbene (TS) and its derivatives (namely, resveratrol and pterostilbene). They represent different classes of organic compounds promising for organic electronics and biomedical applications. Regarding their physical properties, they range from non-polar (TS) to polar ones that can clarify the regularities of a weak vdW interaction and its influence on spectroscopic properties. Raman scattering was demonstrated to be the most effective spectroscopic technique to confirm complex formation. The vibrations localized on functional groups with excess positive (negative) charge (e.g., benzene rings (macrocycle) in TPP) exhibit blue-shifted (red-shifted) fingerprints lines in Raman spectrum of complex with respect to the spectra of pure compounds. These trends were also confirmed by DFT calculations. The THz absorption spectra of the vdW complexes demonstrated additional weak bands that can be assigned to the librations of molecules relative to the hBN surface, thus confirming the formation of the complex. Electronic spectroscopy (particularly fluorescence) is less effective in identifying the formation of weakly bonded vdW complexes (TS+hBN), which exhibits the relative enhancement of the TS vibronic line and a slightly faster fluorescence decay. However, it becomes more effective for polar TPP, whose vdW complex with hBN demonstrates notable red shifts in both UV/vis absorption and fluorescence spectra.

This work was supported by the Horizon Europe FLORIN project (No. 101086142) and the Research Council of Lithuania (Grant No. S-MIP-23-70).