Chiral recognition as well as chirality transfer in supramolecular self-assembly and on-surface coordination is studied for the enantiopure 6,13-dicyano[7]helicene building block. It is remarkable that, with this helical molecule, both H-bonded chains and metal-coordinated chains can be formed on the same substrate, thereby allowing for a direct comparison of the chain bonding motifs and their effects on the self-assembly in experiment and theory. Conformational flexure and both adsorbate/adsorbent and intermolecular interactions can be identified as factors influencing the chiral recognition at the binding site. The observed H-bonded chains are chiral, however, the overall appearance of Cu-coordinated chains is no longer chiral. The study was performed via scanning tunneling microscopy, X-ray-photoelectron spectroscopy and density functional theory calculations. We show a significant influence of the molecular flexibility and the type of bonding motif on the chirality transfer in the 1D self-assembly.

A bottom-up approach is introduced to fabricate two-dimensional self-assembled layers of molecular spin-systems containing Mn and Fe ions arranged in a chessboard lattice. We demonstrate that the Mn and Fe spin states can be reversibly operated by their selective response to coordination/decoordination of volatile ligands like ammonia (NH3).

The controlled manipulation of spin states in atoms/molecules is of profound interest towards the design of future spin-based devices. [1,2] A prominent example of how spin states are modified (S = 2$S = 0) can be found in natures Fe II porphyrin moiety within hemoglobin and its coordination with the O 2 ligand.[3] Recently, we have implemented this concept in a synthetic on-surface arrangement using metallo-porphyrins adsorbed on ferromagnetic surfaces. By axial coordination with an external NO ligand the induced magnetic moment in the (S = 1/2) Co II porphyrin has been switched-off. [4] These experiments depend on a characteristic property of paramagnetic metallo-porphyrins as well as phthalocyanines: their interfacial chemical interaction with the ferromagnetic surface ligand induces a magnetic moment stable up to room temperature. [4,5] Axial coordination can also be used to control the magnetic anisotropy [6] as well as the strength and sign of the exchange interaction.[4b]Controlling on-surface/interface spin systems [4, 5j,k, 6, 7] is a prerequisite for applications in organic spintronics [1] which makes this research field increasingly popular. Recently, we combined chemically directed self-assembly and coordination chemistry to obtain selectively switchable, highly ordered supramolecular 2D spin arrays.[5j] Concerning chemical control of the magnetic moment, only off-switching [4, 5j] and spintuning, [4b, 5k] that is, switching spin-on!spin-off and spin-on! spin-on' (a modified spin state) have been established. So far this set of on-surface chemical spin operations was incomplete since the spin-off!spin-on case was missing. Generally, switching the spin in organometallic complexes by external ligands to the on-state is more difficult to achieve than switching to the off-state, since chemical bonding has to overcome the spin-pairing energy. An additional complication arises from the possibility that the surface can modify the spin states before as well as after the axial ligation.[4b] This can also lead to spin-quenching on the surface. [4b, 8] Here we report on the first demonstration of an on-surface chemical spin onswitch, for Ni II porphyrins (S = 0) adsorbed on a ferromagnetic (FM) Co substrate, by the diamagnetic (S = 0) external NH 3 ligand. A schematic representation of this spin on-switch (S = 0$S = 1) is shown in Figure 1 a.To study this effect, Ni II tetraphenylporphyrin (NiTPP; see Figure 1 a) molecules were thermally sublimed in ultrahigh vacuum onto clean Co thin films on Cu(001) single crystals. [4, 5e,f,j] For a description of the methods see the Supporting Information.In scanning tunneling microscopy (STM) experiments (Figure 1 b), we consistently find the molecules adsorbed in a random fashion on Co and Ni substrates, [4, 5f] in contrast to self-assembly of NiTPP on Au and Ag substrates.[9a] Most of the NiTPP molecules on the Co surface can be recognized as rectangular shapes-the so-called saddle-shape conformation [9b] (Figure 1 c), whereas a minority of the molecules is obse...

ABSTRACT:The formation of on-surface coordination polymers is controlled by the interplay of chemical reactivity and structure of the building blocks, as well as by the orientating role of the substrate registry. Beyond the pre-determined patterns of structural assembly, the chemical reactivity of the reactants involved may provide alternative pathways in their aggregation. Organic molecules, which are transformed in a surface reaction, may be subsequently trapped via coordination of homo-or heterometal adatoms, which may also play a role in the molecular transformation itself. The amino-functionalized perylene derivative, 4,9-diaminoperylene-quinone-3,10-diimine (DPDI), undergoes specific levels of dehydrogenation (-1 H 2 or -3 H 2 ) depending on the nature of the present adatoms (Fe, Co, Ni or Cu, respectively). In this way, the molecule is converted to an endo-or an exo-ligand, possessing a concave or convex arrangement of ligating atoms, which is decisive for the formation of either 1D or 2D coordination polymers.

The Shockley surface state on Cu(111) reacts sensitively to the perturbation by molecular adsorbates on the surface. In the porous structure of a metal-coordinated molecular network on Cu(111), the surface state is confined to a series of discrete states. Energy and momentum of eigenstates in the pores are related to both the energy dispersion of the free surface state and the geometric and energetic details of the confining barrier formed by the molecular network. The penetration of the confined state into the barrier is found to be sensitive to the constituting architectural elements.