Mechanochemical Molecular Migration on Graphene

Abstract

In this study, we propose that the curvature of graphene can be exploited to perform directional molecular motion and provide atomistic insights into the curvature-dependent molecular migration through density functional theory calculations. We first reveal the origin of the different migration trends observed experimentally for aromatic molecules with electron-donating and -withdrawing groups on p-doped functionalized graphene. Next, we show that the kinetic barrier for migration depends on the amount and nature of the curvature, that is, positive versus negative curvature. We find that the molecular migration on a wrinkled/rippled graphene sheet preferentially happens from the valley (positive curvature) to the mountain (negative curvature) regions. To understand the origin of such curvature-dependent molecular motion and migrational kinetic barrier trends, we develop a descriptor based on the frontier orbital orientation of graphene. Finally, based on these findings, we predict that time- and space-varying curvature can drive directional molecular motion on graphene and thus further propose that efforts should focus on exploring other two-dimensional materials as active platforms for performing controlled molecular motion.

Studies of the Reactivity of Graphene Driven by Mechanical Distortions

“…To this end, the π-orbital axis vector (POAV) method − was developed to quantify the effect of distortion/strain on the π-orbitals for carbon atoms in conjugated aromatic compounds. It was hypothesized that mechanochemical strain can influence the electron delocalization as the orientation of the orbitals participating in the π-bond formation changes, and recently, we demonstrated that POAV-derived quantities, such as the angle between two POAVs, can also explain kinetic barriers associated with molecular migration on curved graphene, that others have experimentally observed, which can impact how aryl compounds either react to or migrate across, graphene surfaces …”

“…To further understand the origin of the destabilization of curved graphene in comparison to flat graphene, we construct a theoretical model based on POAV approach (shown in Figure b, here, V ⃗ π is the POAV) developed previously. − According to the POAV analysis, the carbon atom π-orbitals in locally distorted conjugated organic species experience greater chemical reactivity due to the decreased π electron delocalization. − The angle between the two adjacent POAVs is defined as “POAV angle,” which has been shown to capture the effect of local curvature on molecular migration barriers on curved graphene . Here, we have adapted the POAV angle descriptor approach to understand the Δ E trends as a function of nanoparticle diameter.…”

“…30−32 The angle between the two adjacent POAVs is defined as "POAV angle," which has been shown to capture the effect of local curvature on molecular migration barriers on curved graphene. 34 Here, we have adapted the POAV angle descriptor approach to understand the ΔE trends as a function of nanoparticle diameter. Specifically, we use the POAV angle between the 2p z orbitals of the curved graphene near the region of 4-NBD functionalization center (Figure 7a) such that a higher POAV angle value corresponds to more distortion from a planar sp 2 graphene structure.…”

“…Furthermore, we modeled the reactivity of graphene with 4-NBD using density functional theory calculations to determine the influence of the curvature of graphene on both the activation barrier for reaction and the overall reaction energy for functionalization. We then applied a descriptor 34 based on the POAV angle to understand the reactivity trend of graphene with little curvature, representative of being deposited on a flat surface, and graphene with varying curvature, representative of being deposited on films consisting of nanoparticles with variable diameters. The results presented herein may provide a guide for carrying out spatially controlled reactions on graphene through controlled lattice distortions.…”

Examining the Long-Range Effect in Very Long Graphene Nanoribbons: A First-Principles Study

“…Graphene nanoribbons (GNRs) have attracted a lot of attention in recent years due to their excellent properties and electronic structures that can be tuned by size and edge shape. − Other factors such as doping and curvature also bring various new properties to GNRs for many potential applications. For example, H or N doping can modulate the band gap of GNRs, allowing the transition of GNR-based materials between conductive and semiconductive. − Curvature can modulate the front orbitals of GNRs, thereby changing the migration direction of adsorbed molecules on GNRs …”