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

Abstract

We report the synthesis and first electronic characterization of an atomically thin two dimensional p-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 CC coupling of the resulting Agbound 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.

Compounds bearing multiple photoreactive chalcone units: Synthesis and study towards 2D polymerization in Langmuir monolayers

“…The 2D polymerization in a single crystal and at the air/water interface involved monomers in which UV-induced reactions such as [4 þ 4] cycloaddition of anthracene [5e7] and 1,8-diazaanthracene [8], carbonization of hexayine amphiphiles [9], and [4 þ 2] cycloaddition of anthracene and acetylene [10] subunits occurred. An alternative approach to 2D polymers involved the Ullmann reaction in which halogenated monomers were covalently connected on the surface of a metal crystal [11,12]. Additionally, there are a few examples of using the metal surface as a template to prepare 2D polymers through different addition [13] and condensation [14,15] reactions.…”

Surface-confined 2D polymerization of a brominated copper-tetraphenylporphyrin on Au(111)

“…Especially, the prospect to fabricate π-conjugated graphene-like nano-sheets of controlled dimensions is of great interest. 14 It was reported that dehalogenation started already at reduced temperature and is nearly finished at room temperature [15][16][17] , especially on the reactive Cu surfaces. [4][5][6][7][8] One major approach for surface-confined polymerization is the halogen-based covalent self-assembly based on the Ullmann coupling reaction.…”

Hierarchical on-surface synthesis and electronic structure of carbonyl-functionalized one- and two-dimensional covalent nanoarchitectures

“…The bond flexibility in the molecular building blocks and the irreversibility of the newly formed C–C bond prohibit an error correction during the network formation, which leads readily to equilibrium-disordered structures of limited size19. Therefore, electronic properties of bottom-up fabricated 2D networks remain experimentally widely unexplored20, despite the exciting physical properties such as a half-metallic character21 or band structures with Dirac-cone-like crossings and linear band dispersion predicted by density functional theory (DFT)222324. In line with graphene nanoribbons, porous graphene exhibits a band gap that can be controlled by the pore size, density, functionalization and geometry25.…”