Self-Assembly and Orbital Imaging of Metal Phthalocyanines on a Graphene Model Surface

Abstract

Metal phthalocyanines (MPc) form a tunable class of molecules, where both the central metal ion and the organic macrocycle can be modified. This allows the electronic properties and self-assembly of these molecules to be tuned over a broad range. We focus on cobalt phthalocyanine (CoPc), copper phthalocyanine (CuPc), and fully fluorinated cobalt phthalocyanine (F 16 CoPc) and study their self-assembly on epitaxial graphene. We investigate the energetic positions and symmetries of the frontier molecular orbitals by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) experiments and density functional theory (DFT) calculations. Our results shed light on the molecular ordering and the energies of molecular orbitals with respect to the graphene Dirac point for the different MPcs. This information will be crucial for using molecular overlayers to modify the electronic properties of graphene.

Surface chemistry of porphyrins and phthalocyanines

“…Detailed imaging of frontier orbitals by dI/dV mapping and comparison with computed results has been reported for CoPc, CuPc and CoPcF 16 on graphene/Ir(111) (cf. Section 4.1.2 for discussion of the structural properties of this system) [305]. For 2HPc on graphene/Ir (111), physisorptive adsorbate-substrate bonding and a planar adsorption geometry was observed, whereas covalent bonding and substantial deformation occurred on Ir(111) [308].…”

“…The molecular self-assembly was then predominantly driven by intermolecular interactions, while the hexagonal symmetry of the graphene substrate was not transferred to the phthalocyanine adsorbate layer. For example, Järvinen et al used graphene/Ir (1 1 1) to study the self-assembly of CoPc, CuPc and CoPcF 16 [305,306]. On this substrate, the complexes readily formed densely packed 2D stuctures with an almost square lattice in the cases of CoPc and CuPc, while CoPcF 16 formed an oblique lattice (cf.…”

Noncovalent interactions of free-base phthalocyanine with elongated fullerenes as carbon nanotube models

“…However, even in this case, the information afforded is often unable to provide a necessary insight into the mechanism of interaction of organic functionalizing species with a carbon nanomaterial. This fact makes one appeal to theoretical tools, in particular to DFT calculations, to fill the above gap, as exemplified in a number of works on Pc hybrids with fullerenes [2][3][4][5][6][7][8][9][10] and graphene [11][12][13][14][15][16][17]. As regards related CNT-based systems, the reports in which theoretical modeling are explored to assist experimental characterization turn to be very scarce [19,20,22].…”

Comparing the Self‐Assembly of Sexiphenyl‐Dicarbonitrile on Graphite and Graphene on Cu(111)

“…[26] However,i ts hould be noted that a discrepancy between calculated band gap and STS measure- ments could also be the result of temporary charging of the molecule [27] facilitatedb yad ouble barriert unnel junction. [28,29] In as econd step, we lookeda tt he adsorption of NC-Ph 6 -CN on graphene by comparing an individually adsorbed molecule, au nit cell without shift, and au nit cell that incorporatesashift every fourth molecule ( Figure S3). [30] Withouts hift, we determined au nit cell of a = 2.9 nm, b = 0.7 nm, V = 908.T he unit cell with shift of every fourth molecule was a = 2.9 nm, b = 2.2 nm, V = 908 (Figure 3b), agreeing reasonably well with our experimental values.…”