Luis Cardenas

Insight into Organometallic Intermediate and Its Evolution to Covalent Bonding in Surface-Confined Ullmann Polymerization

We provide insight into surface-catalyzed dehalogenative polymerization, analyzing the organometallic intermediate and its evolution into planar polymeric structures. A combined study using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and first-principles calculations unveils the structural conformation of substrate-bound phenylene intermediates generated from 1,4-dibromobenzene precursors on Cu(110), showing the stabilizing role of the halogen. The appearance of covalently bonded conjugated structures is followed in real time by fast-XPS measurements (with an acquisition time of 2 s per spectrum and heating rate of 2 K/s), showing that the detaching of phenylene units from the copper substrate and subsequent polymerization occur upon annealing above 460 ± 10 K.

Synthesis and electronic structure of a two dimensional π-conjugated polythiophene

We report the synthesis and first electronic characterization of an atomically thin two dimensional π-conjugated polymer. Polymerization via Ullmann coupling of a tetrabrominated tetrathienoanthracene on Ag(111) in ultra-high vacuum (UHV) produces a porous 2D polymer network that has been characterized by scanning tunnelling microscopy (STM). High-resolution X-ray photoelectron spectroscopy (HRXPS) shows that the reaction proceeds via two distinct steps: dehalogenation of the brominated precursor, which begins at room temperature (RT), and C–C coupling of the resulting Ag-bound intermediates, which requires annealing at 300 °C. The formation of the 2D conjugated network is accompanied by a shift of the occupied molecular states by 0.6 eV towards the Fermi level, as observed by UV photoelectron spectroscopy (UPS). A theoretical analysis of the electronic gap reduction in the transition from monomeric building blocks to various 1D and 2D oligomers and polymers yields important insight into the effect of topology on the electronic structure of 2D conjugated polymers.

Transformations of Molecular Frameworks by Host–Guest Response: Novel Routes toward Two-Dimensional Self-Assembly at the Solid–Liquid Interface

We review recent new avenues for controlling two-dimensional (2D) self-assembly stabilized by non-covalent interactions. The use of host–guest architectures has opened new pathways for supramolecular self-assembly in two dimensions by immobilizing molecules of interest in 2D nano-porous networks. We also describe how a judicious choice of guest molecule can induce effective changes in host templates. These transformations could enable full control of 2D self-assembly with nanoscale precision, by tuning parameters such as stoichiometry, geometry and non-covalent interactions. This approach is of paramount importance for understanding changes of dimensionality and subsequently the formation of 2D and 3D supramolecular networks and ordered films that can be used as active materials for applications (e.g., electronic devices).