Emergence of localized in-gap states in conjugated polymers of branched topology

Abstract

Using cryogenic scanning tunneling microscopy and spectroscopy, we investigated cross-linked phenyelenebased polymers with various branched morphology at a single-molecule resolution. We found that localized states that are in the band gap of un-branched polymers emerge at the branch junctions. These in-gap states can be shifted close to the Fermi level through three means: extending the length of branch arms, coupling adjacent branches in hyperbranched structures, or increasing the number of branch arms. Single-band tight-binding calculations can reproduce all experimental results and provide quantitative relationships between the energy level shifts and the branching geometry. Our discovery evidences the emergence and development of in-gap states in the band structures of conjugated systems with fractional dimensions.

Combined Photoemission and Scanning Tunneling Microscopy Study of the Surface-Assisted Ullmann Coupling Reaction

“…The photoemission data shown in the previous sections clearly indicate that the adsorbed DBTP and TBB molecules on Cu(111) undergo substantial chemical changes at temperatures above 170 K. In the following, we will provide STM results to cover morphological aspects. STM data of DBTP on Cu(111) have already been presented in previous studies authored by some of us. ,,, We found that at 300 K DBTP monomers undergo debromination reactions and the resultant (ph) 3 biradicals are linked by single Cu atoms forming a polymeric organometallic intermediate; above 470 K, the C–C coupling takes place, and the intermediate is converted into poly( para -phenylene) oligomers, while the Cu atoms are released. In this section, we focus on TBB.…”

Electronic band dispersion of graphene nanoribbons via Fourier-transformed scanning tunneling spectroscopy

“…By mapping out these standing waves in the LDOS as a function of position and sample bias, STS can be used to reconstruct the energy-momentum relation for both occupied and empty electronic states 12,13 . Systems studied so far by this approach include defects in graphene 14 , carbon nanotubes 15 and high-T c superconductors 16 , but also the ends of carbon nanotubes 17 as well as short polyphenylene chains 18,19 .…”

Ullmann Reaction of Aryl Chlorides on Various Surfaces and the Application in Stepwise Growth of 2D Covalent Organic Frameworks

“…Ever since the pioneering work of Grill et al in 2007, on-surface synthesis of organic monomer-based COFs under ultrahigh vacuum (UHV) has emerged as a powerful bottom-up fabrication strategy, which has been the subject of intense atomic investigations using scanning tunneling microscopy (STM) . Of the various organic reactions achieved on surfaces under ultrahigh vacuum, Ullmann reactions of aryl bromides and iodides have proven powerful for constructing diverse macromolecular systems, including polymeric chains, hyperbranched oligomers, graphene ribbons, porous molecular networks, super honeycomb frameworks, and other stuctures …”