Off-Center Rotation of CuPc Molecular Rotor on a Bi(111) Surface and the Chiral Feature

Abstract

Molecular rotors with an off-center axis and the chiral feature of achiral CuPc molecules on a semi-metallic Bi(111) surface have been investigated by means of a scanning tunneling microscopy (STM) at liquid nitrogen (LN2) temperature. The rotation axis of each CuPc molecular rotor is located at the end of a phthalocyanine group. As molecular coverage increases, the CuPc molecules are self-assembled into various nanoclusters and finally into two-dimensional (2D) domains, in which each CuPc molecule exhibits an apparent chiral feature. Such chiral features of the CuPc molecules can be attributed to the combined effect of asymmetric charge transfer between the CuPc and Bi(111) substrate, and the intermolecular van der Waals interactions.

Atomic Scale Investigation of the CuPc–MAPbX3 Interface and the Effect of Non-Stoichiometric Perovskite Films on Interfacial Structures

“…The α-polymorph of CuPc (α-CuPc) features a b -axis periodicity of 3.8 Å and a stacking angle of approximately 63°. , The CuPc SA layers measured on MAPbI 3 exhibit periodicity along an angle of 61 ± 2° (red line, Figure b), which is consistent with the α-phase CuPc stacking angle, suggesting that CuPc molecules may also stack at this angle in the observed SA layer. The measured value of 1.14 ± 0.04 nm for the c -axis spacing is slightly lower than but nearly consistent with the value of 1.2 nm reported in the literature for α-CuPc. , It should also be noted that a wide range of c -axis spacings (1.18–1.69 nm) have been reported for CuPc SA layers on other substrates. − Notably, both the c -axis and b -axis periodicities observed here match well the values for a CuPc layer on Bi 2 Se 3 . Importantly, the b -axis periodicity in these studies is larger than the expected 3.8 Å spacing of α-CuPc; therefore, the exact stacking structure may be due to some modification of the α-CuPc structure.…”

“…In both cases, the height value is significantly less than the 1.4–1.9 nm layer height expected if CuPc molecules are adsorbed edge-on. 28 , 32 The measured SA layer height is also less than the measured molecular width of CuPc ( Figure S8 ), which gives a first approximation of the apparent step height of the SA layer if the molecule was adsorbed edge-on. This implies two possibilities: (1) the CuPc molecules are adsorbed edge-on, but the measured apparent height is strongly influenced by electronic effects or (2) the measured value does represent the true physical height of the SA layer but the CuPc molecules are adsorbed at some tilt angle, θ, relative to the MAPbI 3 film.…”

Molecular Engineering of Multifunctional Metallophthalocyanine-Containing Framework Materials

“…STM images of (a) CuPc with a tetrameric unit cell on Au(111), (b) the second layer of the CuPc films consisting of parallel standing up CuPc chains, (c) a full monolayer of TiOPc with honeycomb phase on Ag(111), and (d) an ordered square binary molecular network formed by a chloroaluminum phthalocyanine molecule and perfluoropentacene in a molecular ratio of 2:1 on HOPG . (e)−(h) are the corresponding structural models for (a)−(d), respectively.…”

“…Copyright 2019 The Royal Society of Chemistry. (b and f) Reprinted with permission from ref . Copyright 2017 MDPI (http:// creativecommons.org/licenses/by/4.0/).…”

“…229 CuPc's strong interaction with the Au(111) surface led to a slight deviation of the HOMO (−1.5 eV) of CuPc. When adsorbed on a Dirac material such as graphene, CuPc molecules self-assembled into a parallel perpendicular chainlike structure (Figure 9b,f) and shifted the HOMO level of CuPc to −1.3 V. 229,235 A slight reduction of the HOMO− LUMO gap of CuPc can be observed as compared to that on the Au(111) substrate. The MPc−substrate interaction also seems to be related to the identity of the metal center.…”