Perchlorination of Coronene Enhances its Propensity for Self‐Assembly on Graphene

Abstract

Providing a quantitative understanding of the thermodynamics involved in molecular adsorption and self-assembly at a nanostructured carbon material is of fundamental importance and finds outstanding applications in the graphene era. Here, we study the effect of edge perchlorination of coronene, which is a prototypical polyaromatic hydrocarbon, on the binding affinity for the basal planes of graphite. First, by comparing the desorption barrier of hydrogenated versus perchlorinated coronene measured by temperature-programmed desorption, we quantify the enhancement of the strength of physisorption at the single-molecule level though chlorine substitution. Then, by a thermodynamic analysis of the corresponding monolayers based on force-field calculations and statistical mechanics, we show that perchlorination decreases the free energy of self-assembly, not only enthalpically (by enhancing the strength of surface binding), but also entropically (by decreasing the surface concentration). The functional advantage of a chemically modulated 2D self-assembly is demonstrated in the context of the molecule-assisted liquid-phase exfoliation of graphite into graphene.

Predicting molecular self-assembly at surfaces: a statistical thermodynamics and modeling approach

“…Also, the results indicate that chlorine substitution (L12), which enhances surface adsorption relative to C12, versus alcohol functionalization (B12), which strengthens molecular recognition in the SAM by H-bonding, produce similar effects. Taken together and consistent with a recent report by us, 30 these results suggest that chemical tailoring of the molecular components is a potentially useful strategy to modulate molecular self-assembly at surfaces and interfaces.…”

“…To illustrate this aspect, the 2D self-assembly of coronene (COR) and perchlorocoronene (CLC) were compared. As discussed elsewhere, 30 a perchloro functionalization of coronene was found to enhance the 2D self-assembly propensity both energetically and entropically. Using eqn (22), a phase diagram for the competitive self-assembly of these two molecules on graphite can be built by comparing the surface free energy of the corresponding SAMs as a function of the concentration of COR (x axis) versus CLC (y axis) in solution; see Fig.…”

“…(1) strongly interacting benzenecarboxylic acids, such as isophthalic acid (ISA), 36 terephthalic acid (TRA), 36 and trimesic acid (TMA); 16,37 (2) two bases, N 9 -ethyl guanine (GUA) 38 and melamine (MEL), 39 whose self-assembly is steered by multiple hydrogen bonds; (3) a series of linear alkanes with a chain length of twelve that are substituted at one terminus with one carboxylic group (A12), 14 one hydroxyl group (B12), 40 one chlorine group (L12), 41 or nothing (C12); [40][41][42] and (4) two large poly-aromatic hydrocarbons, coronene (COR) 30,43 and perchlorocoronene (CLC). 30 An illustration of the modeled SAMs, which span a wide range of molecular size, density of packing and energy of interaction is given in Fig. 3.…”

“…In fact, since g is proportional to Dm AB , 2D self-assembly will occur if and only if g is lower than zero. In addition, since g is architecture-dependent through both the strength of molecular recognition in the monolayer (E sam 0 ) and the density of packing (A uc 0 ), its numerical evaluation allows one to compare the relative stability of different SAMs, which is useful to explore competitive equilibria at surfaces 29,30 and rationalize the concentration-dependent 2D polymorphism. 25,26,44 To illustrate this aspect, we analyzed the concentration dependence of trimesic acid (TMA) self-assembly, which was shown by the STM to form three distinct monolayers: (1) the porous hexagonal or chickenwire (CHK) architecture; (2) the slightly more dense flower (FLW); and (3) the densely-packed superflower (SFW); see Fig.…”

Enhanced liquid phase exfoliation of graphene in water using an insoluble bis-pyrene stabiliser

“…the adsorption of the pyrene binding group on the graphene surface, the affinity of the functional groups for the solvent medium, and the effectiveness of deterrence of re-stacking of graphene sheets. 9,10,[26][27][28] Since the affinity of the functional groups for the solvent medium of the functional groups is one of the key parameters, stabilisers with relatively good aqueous solubility have been used up to now.…”