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2024
15. A self-healing crystal that repairs multiple cracks.
Javed R. Pathan, Haripriya Balan, Patrick Commins, Arthi Ravi, Marieh B. Al-Handawi, Ian Cheng-Yi Hou, Panče Naumov* and Kana M. Sureshan*.
Journal of the American Chemical Society doi:10.1021/jacs.4c09334 (2024)
14. Smart molecular crystal switches.
Ian Cheng-Yi Hou, Liang Li, Hongyu Zhang and Panče Naumov.
Smart Molecules doi:10.1002/smo.20230031 (2024)
Molecular switches that function in the crystalline state exhibit unique behaviors distinct from those in solution. This review highlights recent progress in smart molecular crystal switches based on molecular martensites, which undergo reversible state changes in response to external stimuli while maintaining crystal integrity. Most switches are triggered by temperature or mechanical stress, with emerging stimuli such as photothermal processes, photoisomerization, and host–guest interactions. Their ability to modulate molecular orientation and interactions enables applications in actuators, reconfigurable structural materials, optoelectronics, magnetics, and switchable porous systems. Continued advances position smart molecular crystal switches as promising components in future technologies and interdisciplinary innovation.
2022
Dr. Ian Cheng-Yi Hou, Dr. Antoine Hinaut, Sebastian Scherb, Prof. Ernst Meyer, Prof. Akimitsu Narita and Prof. Klaus Müllen.
Chemistry-An Asian Journal doi:10.1002/asia.202200220 (2022)
Dendritic polyphenylenes (PPs) can act as nanographene (NG) precursors when their structures form non-overlapping 2D benzene networks. We synthesized two giant dendritic PPs containing 366 and 546 carbon atoms using a layer-by-layer growth strategy. While solution-phase cyclodehydrogenation was unsuccessful, electrospray deposition under ultrahigh vacuum enabled their preparation on metal surfaces. Scanning probe microscopy revealed thermally induced partial planarization on the substrate, offering insight into converting large dendritic PPs into NGs on surfaces.
2021
12. Dicyclopentaannelated Hexa-peri-hexabenzocoronenes with a Singlet Biradical Ground State.
Dr. Qiang Chen, Prof. Dr. Martin Baumgarten, Dr. Manfred Wagner, Dr. Yunbin Hu, Dr. Ian Cheng-Yi Hou, Prof. Dr. Akimitsu Narita and Prof. Dr. Klaus Müllen.
A Journal of the German Chemical Society doi:10.1002/anie.202102932 (2021)
2020
11. Proton-Gated Ring-Closure of a Negative Photochromic Azulene-Based Diarylethene.
Ian Cheng-Yi Hou, Fabian Berger, Prof. Akimitsu Narita, Prof. Klaus Müllen and Prof. Stefan Hecht.
A Journal of the German Chemical Society doi:10.1021/anie.202007989 (2020)
Proton-responsive photochromic molecules are valuable for rapid, non-invasive optical control, yet their protonation sites typically reside on heteroatoms, separate from the photoactive π-system. We introduce an azulene-containing diarylethene photoswitch in which protonation occurs directly on the hydrocarbon framework. This design enables a proton-gated negative photochromic ring-closure with significantly enhanced optical responses in both open and closed forms compared to heteroatom-based analogues. NMR and theoretical studies confirm protonation on the π-system as the origin of this unique behavior. These findings highlight the potential of non-alternant hydrocarbons in creating multi-responsive molecular switches.
Ian Cheng-Yi Hou, Qiang Sun, Kristjan Eimre, Marco Di Giovannantonio, José I. Urgel, Pascal Ruffieux, Akimitsu Narita*, Roman Fasel* and Klaus Müllen*.
Journal of the American Chemical Society doi:10.1021/jacs.0c03635 (2020)
Pentagon–heptagon pairs are common topological defects in graphene and critically affect its properties, yet constructing sp²-carbon frameworks with multiple ordered pentagon–heptagon fusions remains challenging. We show that the azulene unit in an organometallic polymer undergoes thermal rearrangement on Au(111), forming new sp²-carbon architectures with regularly fused pentagon–heptagon motifs. High-resolution scanning probe microscopy reveals their unique polycyclic structures, while aromaticity calculations indicate a distinctive polar electronic character. This work provides a new route to defect-engineered graphene-like materials.
9. Stepwise Lateral Extension of Phenyl-Substituted Linear Polyphenylenes.
Ian Cheng-Yi Hou, Akimitsu Narita and Klaus Müllen.
Macromolecular Chemistry and Physics doi:10.1002/macp.201900374 (2020)
Polyphenylenes (PPs) are mechanically robust and chemically stable polymers with potential membrane and nanoelectronic applications. Phenyl-substituted linear PPs also act as bottom-up precursors to graphene nanoribbons (GNRs). Introducing properly oriented branched phenyl groups can laterally expand PPs without ring overlap, enabling access to wider GNRs with tunable electronic properties; however, current widths remain limited to ≈2 nm. We report a stepwise lateral extension strategy for phenyl-substituted PPs using Diels–Alder cycloadditions between ethynyl-functionalized PP backbones and diphenylcyclopentadienones, followed by deprotection. Structural evolution is confirmed by NMR, IR, and gel permeation chromatography. This approach provides a new route to branched PPs that can serve as precursors to wider GNRs with adjustable bandgaps.
2019
Ian Cheng-Yi Hou, Valentin Diez-Cabanes, Agostino Galanti, Michal Valášek, Marcel Mayor, Jérôme Cornil, Akimitsu Narita*, Paolo Samorì* and Klaus Müllen*.
Chemistry of Materials doi:10.1021/acs.chemmater.9b01535 (2019)
Precise control over the self-assembly of functional polycyclic aromatic hydrocarbons (PAHs) and nanographenes (NGs) is crucial for their technological applications. We designed two hexa-peri-hexabenzocoronene (HBC) triads, pAHA and oAHA, each bearing two azobenzene units at pseudo-para and ortho positions, respectively. Both undergo reversible photoisomerization in solution, with oAHA reaching 23% Z-form under UV irradiation (366 nm). Scanning tunneling microscopy revealed that light irradiation modulates their self-assembly at the HOPG/solution interface—unlike previously studied mono-azobenzene HBCs. E–Z isomerization increased packing density; pAHA transformed from an oblique to a rectangular dimer-row lattice, while oAHA maintained a dimer-row motif with altered inter-row orientation. Molecular simulations supported these observations. This work demonstrates light-controlled surface assembly of large π-systems, advancing the design of photoswitchable nanographene-based materials.
Peng Han, Ian Cheng-Yi Hou, Hao Lu, Xiao-Ye Wang, Klaus Müllen, Mischa Bonn, Akimitsu Narita and Enrique Cánovas*.
The Journal of Physical Chemistry Letters doi:10.1021/acs.jpclett.9b00399 (2019)
Graphene quantum dots (GQDs) are promising, tunable, and sustainable sensitizers for solar energy conversion. In this work, atomically precise C₄₂-GQDs (hexa-peri-hexabenzocoronene derivatives) functionalized with a carboxylate group were chemisorbed onto mesoporous metal oxides to improve interfacial charge transfer. Time-resolved THz spectroscopy revealed that chemisorption enhanced electron transfer rates by nearly two orders of magnitude compared to physisorbed GQDs. Complementary DFT calculations, absorption, and valence band XPS analyses attributed this improvement to stronger donor–acceptor coupling induced by covalent bonding. These findings highlight the critical role of surface anchoring in optimizing GQD-based sensitized solar architectures.
6. On-surface synthesis of polyazulene with 2, 6-connectivity.
Qiang Sun‡, Ian Cheng-Yi Hou‡, Kristjan Eimre, Carlo A. Pignedoli, Pascal Ruffieux, Akimitsu Narita and Roman Fasel*.
Chemical Communications doi:10.1039/C9CC07168G (2019)
Azulene, the smallest neutral nonalternant aromatic hydrocarbon, serves not only as a prototype for fundamental studies but also as a versatile building block for functional materials because of its unique opto(electronic) properties. Here, we report the on-surface synthesis and characterization of the homopolymer of azulene connected exclusively at the 2,6-positions using 2,6-diiodoazulene as the monomer precursor. As an intermediate to the formation of polyazulene, a gold-(2,6-azulenylene) chain is observed.
2018
5. Anchor groups for graphene‐porphyrin single‐molecule transistors.
Bart Limburg, James O. Thomas, Gregory Holloway, Hatef Sadeghi, Sara Sangtarash, Ian Cheng-Yi Hou, Jonathan Cremers, Akimitsu Narita, Klaus Müllen, Colin J. Lambert, G. Andrew D. Briggs, Jan A. Mol and Harry L. Anderson.
Advanced Functional Materials doi:10.1002/adfm.201803629 (2018)
Ian Cheng-Yi Hou, Yunbin Hu, Akimitsu Narita and Klaus Müllen.
Polymer Journal doi:10.1002/adfm.201803629 (2018)
The Diels–Alder reaction, known for its catalyst-free nature, functional group tolerance, and efficiency, has become a powerful tool in polymer synthesis. It enables the construction of diverse functional polyphenylenes and ladder polymers with potential applications in membranes and gas separation. More recently, Diels–Alder polymerization has provided tailor-made polyphenylenes serving as precursors for structurally precise graphene nanoribbons (GNRs) with tunable widths, extended lengths (>600 nm), and adjustable bandgaps. This review summarizes recent advances in Diels–Alder polymerization for designing functional polyphenylenes, ladder polymers, and GNRs, highlighting its versatility in building well-defined carbon-based materials.
2017
Ashok Keerthi†§‡, Boya Radha§‡, Daniele Rizzo#, Hao Lu†, Valentin Diez Cabanes∥, Ian Cheng-Yi Hou†, David Beljonne∥, Jérôme Cornil∥, Cinzia Casiraghi#, Martin Baumgarten†, Klaus Müllen*† and Akimitsu Narita*†.
Journal of the American Chemical Society doi:10.1021/jacs.7b09031 (2017)
2. Poly [2 (6)-aminoazulene]: synthesis, photophysical properties, and proton conductivity.
Ian Cheng-Yi Hou, Vijayendra Shetti‡, Shou-Ling Huang, Kun-Lin Liu, Chi-Yang Chao, Song-Cheng Lin, You-Jen Lin, Li-Yin Chen and Tien-Yau Luh *.
Organic Chemistry Frontiers doi:10.1039/C7QO00087A (2017)
Dimeric aminoazulene and poly[2(6)-aminoazulene] are synthesized by Buchwald–Hartwig coupling of the corresponding monomeric carbamatoaminozulenes followed by hydrolysis. The absorption maxima shift from 394 nm for monomeric aminoazulene to 481 nm for the dimer and 591 nm for the polymer. Protonation of the monomeric and polymeric aminoazulenes occurs exclusively at the C1 position(s). The λmax also shows a similar trend at 410, 492 and 670 nm for protonated monomeric, dimeric and polymeric aminoazulenes. These aminoazulenes undergo reversible protonation/deprotonation at the C1 position(s) and both forms exhibit extension of conjugation through amino moieties. Preliminary DFT calculations suggest that the C–N bonds are significantly shortened because of resonance contributions. By incorporating 3 wt% protonated polyaminoazulene in Nafion, the composite membrane has shown 50% reduction in methanol permeability with retention of proton conductivity and 3-fold increment in water permeability, which are advantageous for direct methanol fuel cell application.
2016
1. Hexa‐peri‐hexabenzocoronene with Different Acceptor Units for Tuning Optoelectronic Properties.
Dr. Ashok Keerthi, Ian Cheng-Yi Hou, Dr. Tomasz Marszalek, Prof. Dr. Wojciech Pisula, Prof. Dr. Martin Baumgarten and Dr. Akimitsu Narita.
Chemistry–An Asian Journal doi:10.1002/asia.201600638 (2016)
Hexa-peri-hexabenzocoronene (HBC)-based donor–acceptor dyads were synthesized with three different acceptor units, through two pathways: 1) “pre-functionalization” of monobromo-substituted hexaphenylbenzene prior to the cyclodehydrogenation; and 2) “post-functionalization” of monobromo-substituted HBC after the cyclodehydrogenation. The HBC–acceptor dyads demonstrated varying degrees of intramolecular charge-transfer interactions, depending on the attached acceptor units, which allowed tuning of their photophysical and optoelectronic properties, including the energy gaps. The two synthetic pathways described here can be complementary and potentially be applied for the synthesis of nanographene–acceptor dyads with larger aromatic cores, including one-dimensionally extended graphene nanoribbons.
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