Triphenylene‐Derived Electron Acceptors and Donors on Ag(111): Formation of Intermolecular Charge‐Transfer Complexes with Common Unoccupied Molecular States

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2019-08, Vol.15 (33), p.e1901741-n/a
• Main Authors: Müller, Kathrin, Schmidt, Nico, Link, Stefan, Riedel, René, Bock, Julian, Malone, Walter, Lasri, Karima, Kara, Abdelkader, Starke, Ulrich, Kivala, Milan, Stöhr, Meike
• Format: Article
• Language: English
• Subjects: acceptor molecules; Adsorbates; Charge transfer; charge‐transfer complex; Chemistry; Density functional theory; donor molecules; Donors (electronic); Electron diffraction; Electrons; Materials Science; Molecular orbitals; Nanotechnology; Optoelectronic devices; photoelectron spectroscopy; Photoelectrons; Physics; scanning tunneling microscopy and spectroscopy; Science & Technology - Other Topics; self‐assembly; Silver; Spectrum analysis; Strong interactions (field theory); Substrates; Thin films
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.201901741

Over the past years, ultrathin films consisting of electron donating and accepting molecules have attracted increasing attention due to their potential usage in optoelectronic devices. Key parameters for understanding and tuning their performance are intermolecular and molecule–substrate interactions. Here, the formation of a monolayer thick blend of triphenylene‐based organic donor and acceptor molecules from 2,3,6,7,10,11‐hexamethoxytriphenylene (HAT) and 1,4,5,8,9,12‐hexaazatriphenylenehexacarbonitrile (HATCN), respectively, on a silver (111) surface is reported. Scanning tunneling microscopy and spectroscopy, valence and core level photoelectron spectroscopy, as well as low‐energy electron diffraction measurements are used, complemented by density functional theory calculations, to investigate both the electronic and structural properties of the homomolecular as well as the intermixed layers. The donor molecules are weakly interacting with the Ag(111) surface, while the acceptor molecules show a strong interaction with the substrate leading to charge transfer and substantial buckling of the top silver layer and of the adsorbates. Upon mixing acceptor and donor molecules, strong hybridization occurs between the two different molecules leading to the emergence of a common unoccupied molecular orbital located at both the donor and acceptor molecules. The donor acceptor blend studied here is, therefore, a compelling candidate for organic electronics based on self‐assembled charge‐transfer complexes. Electron acceptor and donor molecules are studied on Ag(111). The acceptor molecules show a strong interaction with the silver, while the donors are only weakly interacting with the surface. Mixing both molecules leads to the formation of a molecular charge‐transfer complex and a common unoccupied state, which was neither found for the pure donor nor for the pure acceptor layers.