A 2D array of electronically coupled quantum boxes is fabricated by means of on-surface self-assembly assuring ultimate precision of each box. The quantum states embedded in the boxes are configured by adsorbates, whose occupancy is controlled with atomic precision. The electronic interbox coupling can be maintained or significantly reduced by proper arrangement of empty and filled boxes.

Acenes and azaacenes lie at the core of molecular materials’ applications due to their important optical and electronic features. A critical aspect is provided by their heteroatom multiplicity, which can strongly affect their properties. Here we report pyrazinacenes containing the dihydro-decaazapentacene and dihydro-octaazatetracene chromophores and compare their properties/functions as a model case at an oxidizing metal substrate. We find a distinguished, oxidation-state-dependent conformational adaptation and self-assembly behaviour and discuss the analogies and differences of planar benzo-substituted decaazapentacene and octaazatetracene forms. Our broad experimental and theoretical study reveals that decaazapentacene is stable against oxidation but unstable against reduction, which is in contrast to pentacene, its C–H only analogue. Decaazapentacenes studied here combine a planar molecular backbone with conformationally flexible substituents. They provide a rich model case to understand the properties of a redox-switchable π-electronic system in solution and at interfaces. Pyrazinacenes represent an unusual class of redox-active chromophores.

A comparative investigation of crystal growth from solution and on-surface assembly in vacuo between copper and three 4'-(2-R-pyrimidin-5-yl)-4,2':6',4''-terpyridines, with R = H (1), Me (2), or Et (3), is presented. In solution, ligand 3 combines with copper(II) acetate or copper(I) triflate in MeOH solution to give [Cu(OAc)(3)] or {[Cu(3)(OMe)(MeOH)][CFSO]·MeOH}. In [Cu(OAc)(3)], paddle-wheel {Cu(μ-OAc)} nodes direct the assembly of one-dimensional (1D) zigzag chains which pack into two-dimensional (2D) sheets. In {[Cu(3)(OMe)(MeOH)][CFSO]·MeOH}, the solvent is a ligand and also generates {Cu(μ-OMe)} units which function as planar 4-connecting nodes to generate a 2D (4,4) net with ligand 3. On Au(111) or Cu(111) surfaces in vacuo, no additional solvent or anions are involved in the assembly. The different substituents in 1, 2, or 3 allow precise molecular resolution imaging in scanning tunneling microscopy. On Au(111), 1 and 2 assemble into close-packed assemblies, while 3 forms a regular porous network. The deposition of Cu adatoms results in reorganization leading to ladder-shaped surface metal-organic motifs. These on-surface coordination assemblies are independent of the 4'-substituent in the 4,2':6',4''-tpy and are reproduced on Cu(111) where Cu adatoms are available during the deposition and relaxation process at room temperature. Upon annealing at elevated temperatures, the original surface assemblies of 1 and 3 are modified and a transition from ladders into rhomboid structures is observed; for 2, a further quasi-hexagonal nanoporous network is observed.

We show that highly ordered two-dimensional (2D) chessboard arrays consisting of a periodic arrangement of two different molecules can be obtained by self-assembly of unsubstituted metal-phthalocyanines (metal-Pcs) on a suitable substrate serving as the template. Specifically, CuPc + MnPc and CuPc + CoPc mixtures sort into highly ordered Cu/Mn and Cu/Co chessboard arrays on the square p(10 × 10) reconstruction of bismuth on Cu(100). Such created bimolecular chessboard assemblies emerge from the site-specific interactions between the central transition-metal ions and the periodically reconstructed substrate. This work provides a conceptually new approach to induce 2D chessboard patterns in that no functionalization of the molecules is needed.

Quantum devices depend on addressable elements, which can be modified separately and in their mutual interaction. Self-assembly at surfaces, for example, formation of a porous (metal-) organic network, provides an ideal way to manufacture arrays of identical quantum boxes, arising in this case from the confinement of the electronic (Shockley) surface state within the pores. We show that the electronic quantum box state as well as the interbox coupling can be modified locally to a varying extent by a selective choice of adsorbates, here C 60 , interacting with the barrier. In view of the wealth of differently acting adsorbates, this approach allows for engineering quantum states in on-surface network architectures.