Unveiling the adsorption mechanism of diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) on pristine graphene via density functional theory.

In this study, we investigated the adsorption mechanism of diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO) on pristine graphene using density functional theory (DFT). Four adsorption orientations were considered to identify the most stable configuration among those investigated. The results suggest that the interaction is governed by physisorption through a combination of π-π stacking, CH···π interactions, P=O···π contacts, and van der Waals forces. Charge density difference (CDD) and independent Gradient Model based on Hirshfeld partition (IGMH) analyses further confirm these noncovalent interactions. The projected density of states (PDOS) shows no new hybridized states near the Fermi level and only a slight perturbation of the graphene C 2p states, consistent with weak physisorption. Furthermore, the work-function shifts upon adsorption are very small (|ΔΦ| ≤ 0.01 eV) and lie within the numerical uncertainty of the method, indicating that molecular orientation has only a minor influence on the interfacial electronic structure. These findings provide molecular-level insight into the adsorption behavior of TPO on graphene and clarify the weak, noncovalent nature of its interaction with the surface.