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Optical absorption signature of a self-assembled dye monolayer on graphene

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ABSTRACT

A well-organized monolayer of alkylated perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) has been formed onto CVD graphene transferred on a transparent substrate. Its structure has been probed by scanning tunnelling microscopy and its optical properties by polarized transmission spectroscopy at varying incidence. The results show that the transition dipoles of adsorbed PTCDI are all oriented parallel to the substrate. The maximum absorption is consistent with the measured surface density of molecules and their absorption cross section. The spectrum presents mainly a large red-shift of the absorption line compared with the free molecules dispersed in solution, whereas the relative strengths of the vibronic structures are preserved. These changes are attributed to non-resonant interactions with the graphene layer and the neighbouring molecules.

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Structural characterization of the self-assembled PTCDI monolayers. Molecular formula of PTCDI-C13 and STM images of self-assembled monolayers on HOPG (a: 14 × 14 nm2) as-grown CVD monolayer graphene on copper foil (b: 11 × 11 nm2) and CVD graphene monolayer transferred onto a PET plate (c: 8 × 8 nm2). The typical current setpoint and sample bias were 10 pA and 800 mV, respectively. The images were acquired at the interface between the substrate and a ca. 10−5 M solution in phenyloctane at room temperature.
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Figure 2: Structural characterization of the self-assembled PTCDI monolayers. Molecular formula of PTCDI-C13 and STM images of self-assembled monolayers on HOPG (a: 14 × 14 nm2) as-grown CVD monolayer graphene on copper foil (b: 11 × 11 nm2) and CVD graphene monolayer transferred onto a PET plate (c: 8 × 8 nm2). The typical current setpoint and sample bias were 10 pA and 800 mV, respectively. The images were acquired at the interface between the substrate and a ca. 10−5 M solution in phenyloctane at room temperature.

Mentions: The PTCDI molecule has become a paradigm both as a self-assembly tecton and as a dye. For the present study, we chose an alkylated form of this dye, N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13), in order to take advantage of the interactions between n-alkyl chains and graphitic substrates for forming a spontaneously self-assembled monolayer at the interface between the solution and graphene. The monolayer structures have been studied by STM at the solution–substrate interface. Intramolecular resolution is possible both with HOPG and graphene as substrates (Fig. 2). As expected from the atomically flat surface of HOPG, this substrate produces the largest domains. It permits an accurate determination of the lattice parameters, which correspond to a surface density of 0.45 molecules per nm2 and a distance between closest neighbours of ca. 1.4 nm. The network obtained on CVD graphene is compatible with that obtained on HOPG, with one molecule per unit cell. The various domains have a finite number of lattice orientations, indicating an epitaxial relationship with the graphitic lattice. These results are fully consistent with the expected formation of a self-assembled monolayer in which the molecules are lying flat on the substrate, with adsorbed n-alkyl chains aligned on the C-atom lattice. By randomly inspecting various regions of drop-cast samples, it appears that a nearly complete coverage (about 80–90%) is obtained whereas the droplet spread on the sample contained the exact quantity of molecules needed to form a monolayer (see Experimental section). The quantitative formation of multilayers can thus be ruled out.


Optical absorption signature of a self-assembled dye monolayer on graphene
Structural characterization of the self-assembled PTCDI monolayers. Molecular formula of PTCDI-C13 and STM images of self-assembled monolayers on HOPG (a: 14 × 14 nm2) as-grown CVD monolayer graphene on copper foil (b: 11 × 11 nm2) and CVD graphene monolayer transferred onto a PET plate (c: 8 × 8 nm2). The typical current setpoint and sample bias were 10 pA and 800 mV, respectively. The images were acquired at the interface between the substrate and a ca. 10−5 M solution in phenyloctane at room temperature.
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Related In: Results  -  Collection

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Figure 2: Structural characterization of the self-assembled PTCDI monolayers. Molecular formula of PTCDI-C13 and STM images of self-assembled monolayers on HOPG (a: 14 × 14 nm2) as-grown CVD monolayer graphene on copper foil (b: 11 × 11 nm2) and CVD graphene monolayer transferred onto a PET plate (c: 8 × 8 nm2). The typical current setpoint and sample bias were 10 pA and 800 mV, respectively. The images were acquired at the interface between the substrate and a ca. 10−5 M solution in phenyloctane at room temperature.
Mentions: The PTCDI molecule has become a paradigm both as a self-assembly tecton and as a dye. For the present study, we chose an alkylated form of this dye, N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13), in order to take advantage of the interactions between n-alkyl chains and graphitic substrates for forming a spontaneously self-assembled monolayer at the interface between the solution and graphene. The monolayer structures have been studied by STM at the solution–substrate interface. Intramolecular resolution is possible both with HOPG and graphene as substrates (Fig. 2). As expected from the atomically flat surface of HOPG, this substrate produces the largest domains. It permits an accurate determination of the lattice parameters, which correspond to a surface density of 0.45 molecules per nm2 and a distance between closest neighbours of ca. 1.4 nm. The network obtained on CVD graphene is compatible with that obtained on HOPG, with one molecule per unit cell. The various domains have a finite number of lattice orientations, indicating an epitaxial relationship with the graphitic lattice. These results are fully consistent with the expected formation of a self-assembled monolayer in which the molecules are lying flat on the substrate, with adsorbed n-alkyl chains aligned on the C-atom lattice. By randomly inspecting various regions of drop-cast samples, it appears that a nearly complete coverage (about 80–90%) is obtained whereas the droplet spread on the sample contained the exact quantity of molecules needed to form a monolayer (see Experimental section). The quantitative formation of multilayers can thus be ruled out.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

A well-organized monolayer of alkylated perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) has been formed onto CVD graphene transferred on a transparent substrate. Its structure has been probed by scanning tunnelling microscopy and its optical properties by polarized transmission spectroscopy at varying incidence. The results show that the transition dipoles of adsorbed PTCDI are all oriented parallel to the substrate. The maximum absorption is consistent with the measured surface density of molecules and their absorption cross section. The spectrum presents mainly a large red-shift of the absorption line compared with the free molecules dispersed in solution, whereas the relative strengths of the vibronic structures are preserved. These changes are attributed to non-resonant interactions with the graphene layer and the neighbouring molecules.

No MeSH data available.