Charge State Control of F₁₆CoPc on h‐BN/Cu(111)

Abstract

The use of molecular materials in solar cells and nano‐electronics demands a fundamental understanding and control of their electronic properties. Particularly relevant is the molecular response to the environment, that is, the interaction with the support and adjacent molecules, as well as the influence of electrostatic gating. Here, the control of molecular level alignment and charge states of fluorinated cobalt phthalocyanines (F16CoPc) on atomically thin hexagonal boron nitride (h‐BN) sheets on Cu(111) is reported using scanning tunneling microscopy (STM) and spectroscopy (STS), as well as atomic force microscopy (AFM) and complementary density functional theory (DFT) calculations. Three parameters that govern the electronic level alignment of F16CoPc orbitals are investigated: i) template‐induced gating by the work function variation of the h‐BN/Cu(111) substrate, ii) gating by the STM tip, and iii) screening by neighboring molecules. The interplay of these parameters influences the charge distribution in the studied molecular arrangements and thus provides the possibility to tune their physicochemical behavior, for instance, the response toward electronic or optical excitation, charge transport, or binding of axial adducts.

Self-assembly and spectroscopic fingerprints of photoactive pyrenyl tectons on hBN/Cu(111)

“…37 V for 2, and 0.39 V for 3, see Figure 6) agree well with the previously reported MO shifts on hBN/Cu(111) (ranging from 0.25 to 0.4 V [28,[35][36][37]) and reflect the local work function variation across the moiré pattern [25,29,30]. In a recent study on F 16 CoPc/hBN/Cu(111), we demonstrated that the local work function difference between the pore and wire regions was preserved upon molecular adsorption [37]. Note, that the smaller shift for the molecule 1 was attributed to the larger distance of the respective wire spectrum from the real wire position (vide supra).…”

“…The colored bars in Figure 5 highlight the energy positions of these frontier orbitals (determined as the bias voltage at the half maximum of the MO leading edge). The observation of well-defined, narrow molecular resonances and large HOMO-LUMO gaps evidenced a reduction of the electronic molecule-support interactions by the hBN spacer layer, as previously reported for adsorbates on hBN/Cu(111) [28,[35][36][37][38] and other hBN/metal supports [18][19][20]79,80]. The dI/dV modulations observed within the gap were attributed to the hBN/Cu(111) support and tip states, respectively (vide infra).…”

“…The rectangular lattice of the X-shaped units corresponded to a densely-packed molecular array (black tetragon in Figure 2), with every unit representing one molecule. The quasihexagonal pattern with larger periodicity (dotted rhombus in Figure 2a) reflected a modulation of the molecular electronic structure imposed by the electronically corrugated hBN/Cu(111) support, as discussed in detail below [18,28,37,38]. The high-resolution STM data in Figure 2b gives a closer look at the intramolecular features.…”

“…The quasihexagonal pattern with larger periodicity (dotted rhombus in Fig. 2 ) reflected a modulation of the molecular electronic structure imposed by the electronically corrugated h BN/Cu(111) support, as discussed in detail below [ 18 , 28 , 37 – 38 ]. The high-resolution STM data in Fig.…”

“…For instance, h BN/Cu(111) [ 24 – 27 ] features a work function template with a moiré superstructure: Depending on the registry of the layer and substrate atoms, the surface is divided in areas of low and high local work function, denoted as “pores” and “wires”, respectively [ 28 – 31 ]. In recent years, our group and others used h BN/Cu(111) to guide the self-assembly of porphyrins [ 28 , 32 – 33 ], decouple perylenetetracarboxylic dianhydride (PTCDA) aggregates [ 34 ], study interfacial charge transfer in binary phthalocyanine arrays [ 35 ], probe vibronic conductance in oligophenylenes [ 36 ], and control the charge state of F 16 CoPc [ 37 ]. Studies focusing on the preparation of coordination networks [ 38 ], wires of polycyclic aromatic hydrocarbons [ 39 ], and graphene patches [ 40 – 41 ] were also performed on h BN/Cu(111).…”