Understanding and optimising the packing density of perylene bisimide layers on CVD-grown graphene

Abstract

ABSTRACT:The non-covalent functionalization of graphene is an attractive strategy to alter the surface chemistry of graphene without damaging its superior electrical and mechanical properties. Using the facile method of aqueous-phase functionalization on large-scale CVDgrown graphene, we investigated the formation of different packing densities in self-assembled monolayers (SAMs) of perylene bisimide derivatives and related this to the amount of substrate contamination. We were able to directly observe wet-chemically deposited SAMs in scanning tunneling microscopy (STM) on transferred CVD graphene and revealed that the densely packed perylene ad-layers adsorb with the conjugated π-system of the core perpendicular to the graphene substrate. This elucidation of the non-covalent functionalization of graphene has major implications on controlling its surface chemistry and opens new pathways for adaptable functionalization in ambient conditions and on the large scale.

On-surface derivatisation of aromatic molecules on graphene: the importance of packing density

“…16 More specifically, we found that graphene with polymer residues from the transfer process produces a lower packing density molecular layer than that of graphene that has been annealed to remove these residues, similar to what has been described by other groups. 17,18 In this communication,…”

“…Despite a large error margin, the overall significantly increased intensity of amine and amide components after annealing indicates that the EDA has at least partially successfully coupled with the -COOH groups on the 1 ''anchor''-molecule. Due to the perpendicular orientation of the molecules on the graphene, 16 we do not expect full coupling to occur as at least one -COOH group will be obscured by the presence of those above. In order to further verify the presence of amine end-groups on the graphene surface, the adhesion of bacteria was tested using fluorescence microscopy.…”

“…20 Generally it is not possible to identify a molecular monolayer by Raman spectroscopy, but due to the GERS effect the Raman signal of the perylene adsorbed on graphene is enhanced. 16,21 The ratio between the 1 peaks and the G band acts as indicator of the packing density of the molecule on the graphene. 16 The high 1 : G ratio of 1.2 obtained from transferring graphene functionalised with 1 is very similar to the ratio (1.5, see ESI †) obtained from our previously reported method of depositing a densely packed layer of 1 on annealed and transferred graphene.…”

“…16,21 The ratio between the 1 peaks and the G band acts as indicator of the packing density of the molecule on the graphene. 16 The high 1 : G ratio of 1.2 obtained from transferring graphene functionalised with 1 is very similar to the ratio (1.5, see ESI †) obtained from our previously reported method of depositing a densely packed layer of 1 on annealed and transferred graphene. 16 We attribute the initial high packing density (HPD) formation to the fact that the as-grown graphene is very clean and the molecular film formation is not disrupted by polymer residue or other contamination.…”

Isomerically Pure Star‐Shaped Triphenylene–Perylene Hybrids Involving Highly Extended π‐Conjugation

“…As recently reported by Duesberg and co‐workers, the ratio between the ν Ag (ca. 1351 cm −1 ) and the G peak of the graphene substrate can be efficiently used as an estimation of the packing density . Indeed, both isomers exhibited very homogeneous mean PDI ν Ag /G ratios of 1.03 and 0.93 (full width at half maximum (FWHM)=0.10 and 0.11) for the C 3 h and C s isomers, respectively, indicative of a high packing density (Figure b).…”