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Quasi-Planar π‑Extended Cycloparaphenylenes: On-Surface Synthesis, Characterization, and Electronic Properties

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Title: Quasi-Planar π‑Extended Cycloparaphenylenes: On-Surface Synthesis, Characterization, and Electronic Properties
Authors: Dong Han, Jakob Schramm, Zilin Ruan, Tim Naumann, Nour-Eddine El Alaoui, Konstantin Y. Amsharov, Ralf Tonner-Zech, J. Michael Gottfried
Publication Year: 2025
Subject Terms: Biophysics, Biochemistry, Cell Biology, Physiology, Pharmacology, Biotechnology, Ecology, Chemical Sciences not elsewhere classified, Physical Sciences not elsewhere classified, scanning tunneling microscopy, reduced gap compared, perylenyl groups bridging, inherent ring strain, increasing ring size, density functional theory, curved aromatic frameworks, 8 – 11, unsubstituted planar parent, rigid bending units, cpps ), hoop, bent benzenoid macrocycles, 8 cpp adopts, electronic properties cycloparaphenylenes, planar cpps provides, electronic properties, planar geometry, phenylene units, electronic structure, planarized cpps
Description: Cycloparaphenylenes (CPPs), hoop-shaped conjugated macrocycles composed of para -linked phenyl units, have attracted significant interest due to their curved aromatic frameworks and para -conjugation, which give rise to unique (opto)electronic properties. Full planarization of their π-systems is structurally inaccessible, as it would further increase the inherent ring strain. However, partial planarization can be achieved by π-extension through incorporation of rigid bending units. Here, we report the on-surface synthesis of quasi-planar π-extended [2n]CPPs (n = 8–11) on Au(111), achieved via a bottom-up surface-assisted strategy, and their characterization by scanning tunneling microscopy/spectroscopy (STM/STS) and density functional theory (DFT). These π-extended CPPs are macrocycles with para -connected phenylenes forming the inner backbone and perylenyl groups bridging the phenylene units. The n = 8 CPP adopts a planar geometry on the surface, while the n = 9 to n = 11 homologues remain nonplanar. Nevertheless, substrate-induced flattening enhances π-orbital overlap and leads to a progressive reduction of the HOMO–LUMO gap with increasing ring size. This behavior is specific for planarized CPPs and contrasts with conventional, nonplanar CPPs. Moreover, π-extension results in a reduced gap compared to the unsubstituted planar parent [2n]CPP. dI/dV maps reveal orbital confinement at the edges and fjord regions, attributed to slower wave function decay. In larger CPPs, the tilted perylenyl groups modulate this confinement and affect the STM contrast in fjord regions. The unique structure of these strained, quasi-planar CPPs provides a well-defined platform for studying the interplay of curvature, conjugation, and electronic structure in bent benzenoid macrocycles.
Document Type: article in journal/newspaper
Language: unknown
DOI: 10.1021/jacs.5c07471.s001
Availability: https://doi.org/10.1021/jacs.5c07471.s001
https://figshare.com/articles/journal_contribution/Quasi-Planar_Extended_Cycloparaphenylenes_On-Surface_Synthesis_Characterization_and_Electronic_Properties/29829131
Rights: CC BY-NC 4.0
Accession Number: edsbas.BC45EDC6
Database: BASE
Description
Abstract:Cycloparaphenylenes (CPPs), hoop-shaped conjugated macrocycles composed of para -linked phenyl units, have attracted significant interest due to their curved aromatic frameworks and para -conjugation, which give rise to unique (opto)electronic properties. Full planarization of their π-systems is structurally inaccessible, as it would further increase the inherent ring strain. However, partial planarization can be achieved by π-extension through incorporation of rigid bending units. Here, we report the on-surface synthesis of quasi-planar π-extended [2n]CPPs (n = 8–11) on Au(111), achieved via a bottom-up surface-assisted strategy, and their characterization by scanning tunneling microscopy/spectroscopy (STM/STS) and density functional theory (DFT). These π-extended CPPs are macrocycles with para -connected phenylenes forming the inner backbone and perylenyl groups bridging the phenylene units. The n = 8 CPP adopts a planar geometry on the surface, while the n = 9 to n = 11 homologues remain nonplanar. Nevertheless, substrate-induced flattening enhances π-orbital overlap and leads to a progressive reduction of the HOMO–LUMO gap with increasing ring size. This behavior is specific for planarized CPPs and contrasts with conventional, nonplanar CPPs. Moreover, π-extension results in a reduced gap compared to the unsubstituted planar parent [2n]CPP. dI/dV maps reveal orbital confinement at the edges and fjord regions, attributed to slower wave function decay. In larger CPPs, the tilted perylenyl groups modulate this confinement and affect the STM contrast in fjord regions. The unique structure of these strained, quasi-planar CPPs provides a well-defined platform for studying the interplay of curvature, conjugation, and electronic structure in bent benzenoid macrocycles.
DOI:10.1021/jacs.5c07471.s001