Insertion of the Liquid Crystal 5CB into Monovacancy Graphene.

Paul A Brown,Daniel Gunlycke,Sean A Fischer,Christopher M Spillmann,Jakub Kołacz

doi:10.3390/molecules27051664

Paul A Brown, Daniel Gunlycke + Show 3 more

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https://doi.org/10.3390/molecules27051664

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Abstract

Interfacial interactions between liquid crystal (LC) and two-dimensional (2D) materials provide a platform to facilitate novel optical and electronic material properties. These interactions are uniquely sensitive to the local energy landscape of the atomically thick 2D surface, which can be strongly influenced by defects that are introduced, either by design or as a byproduct of fabrication processes. Herein, we present density functional theory (DFT) calculations of the LC mesogen 4-cyan-4′-pentylbiphenyl (5CB) on graphene in the presence of a monovacancy (MV-G). We find that the monovacancy strengthens the binding of 5CB in the planar alignment and that the structure is lower in energy than the corresponding homeotropic structure. However, if the molecule is able to approach the monovacancy homeotropically, 5CB undergoes a chemical reaction, releasing 4.5 eV in the process. This reaction follows a step-by-step process gradually adding bonds, inserting the 5CB cyano group into MV-G. We conclude that this irreversible insertion reaction is likely spontaneous, potentially providing a new avenue for controlling both LC behavior and graphene properties.

Highlights

Liquid crystal (LC) on atomically thin 2D interfaces results in unique behaviors such as surface-induced phase transitions [1], tilt angle control [2], selective alignment [3], and ion trapping [4]
The reaction takes several salient steps: (1) an initial bond with a monovacancy carbon pulls the 5CB toward the sheet; (2) the cyano-nitrogen forms a tetrahedral bond with the three carbanions in the monovacancy; (3) the resulting under-coordinated cyano-carbon is pulled further into the monovacancy; (4) one of the three monovacancy carbons unbinds the cyano-nitrogen and binds with the cyano-carbon
From the DOS, we can see that the process is mediated by the conjugated biphenyl core of the molecule

Summary

Introduction

Liquid crystal (LC) on atomically thin 2D interfaces results in unique behaviors such as surface-induced phase transitions [1], tilt angle control [2], selective alignment [3], and ion trapping [4]. 2D materials, including graphene, provide a large surface area for anchoring of atoms or molecules introduced into the system. We expect that defects will play a central role in future applications, as they can provide both control and anchoring sites for absorbates.

Results

Conclusion