Photomodulation of Two-Dimensional Self-Assembly of Azobenzene-Hexa-peri-hexabenzocoronene-Azobenzene Triads

Hou, Ian Cheng-Yi and Diez-Cabanes, Valentin and Galanti, Agostino and Valasek, Michal and Mayor, Marcel and Cornil, Jerome and Narita, Akimitsu and Samori, Paolo and Muellen, Klaus. (2019) Photomodulation of Two-Dimensional Self-Assembly of Azobenzene-Hexa-peri-hexabenzocoronene-Azobenzene Triads. Chemistry of Materials, 31 (17). pp. 6979-6985.

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Achieving exquisite control over self-assembly of functional polycyclic aromatic hydrocarbons (PAH) and nanographene (NG) is essential for their exploitation as active elements in (nano)technological applications. In the framework of our effort to leverage their functional complexity, we designed and synthesized two hexa-peri-hexabenzocoronene (HBC) triads, pAHA and oAHA, decorated with two light-responsive azobenzene moieties at the pseudo-para and ortho positions, respectively. Their photoisomerization in solution is demonstrated by UVâEuro"vis absorption. 1H NMR measurements of oAHA suggested 23% of Z-form can be obtained at a photostationary state with UV irradiation (366 nm). Scanning tunneling microscopy imaging revealed that the self-assembly of pAHA and oAHA at the solidâEuro"liquid interface between highly oriented pyrolytic graphite (HOPG) and their solution in 1,2,4-trichlorobenzene can be modulated upon light irradiation. This is in contrast to our previous work using HBC bearing a single azobenzene moiety, which did not show such photomodulation of the self-assembled structure. Upon E-Z isomerization both pAHA and oAHA displayed an increased packing density on the surface of graphite. Moreover, pAHA revealed a change of self-assembled pattern from an oblique unit cell to a dimer row rectangular crystal lattice whereas the assembly of oAHA retained a dimer row structure before and after light irradiation, yet with a modification of the inter-row molecular orientation. Molecular mechanics/molecular dynamics simulations validated the self-assembly patterns of pAHA and oAHA, comprising azobenzenes in their Z-forms. These results pave the way toward use of suitably functionalized large PAHs, as well as NGs, to develop photoswitchable devices.
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Molecular Devices and Materials (Mayor)
UniBasel Contributors:Mayor, Marcel
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Chemical Society
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:21 Feb 2020 11:26
Deposited On:21 Feb 2020 11:26

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