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Self-Assembled Monolayers of Pseudo‑C2v-Symmetric, Low-Band-Gap Areneoxazolethiolates on Gold Surfaces
journal contribution
posted on 2016-10-11, 00:00 authored by Christoph Partes, Can Yildirim, Swen Schuster, Martin Kind, Jan W. Bats, Michael Zharnikov, Andreas TerfortA series
of three homologous arene[2,3-d]-oxazole-2-thiols
(benzoxazole-2-thiol (BOxSH), naphthaleneoxazole-2-thiol (NOxSH),
and anthraceneoxazole-2-thiol (AOxSH)) were deposited onto Au(111)
to obtain surfaces suitable as injection layers for organic electronics.
The guiding idea was that the increasingly extended conjugated system
would lower the band gap of the films while the introduction of the
annulated heteroaromatic ring would provide the opportunity for pseudosymmetric
attachment of the sulfur anchor, what should lower the conformational
freedom of the system. In fact, the annulation of the oxazole ring
lowers the optical band gaps of the parent compounds to 3.1–4.0
eV, depending on the number of benzene rings. To characterize the
respective monolayers, a variety of spectroscopic techniques such
as ellipsometry, infrared reflection–absorption spectroscopy,
X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine
structure spectroscopy have been utilized. The monolayers of BOxS
exhibit a lower film quality than those of NOxS and AOxS, with enhanced
molecular density and more upright molecular orientation with increasing
molecular length. Infrared spectroscopy suggests that the nitrogen
atoms of the oxazole rings are located more closely to the Au(111)
surface than the oxygen atoms, although no hints for an electronic
interaction between the N atoms and the gold surface could be found.
This preferred orientation could be tentatively traced to packing
effects, solving a conundrum of the literature.
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Keywords
oxazole ringband gapparent compoundsgold surfaceannulated heteroaromatic ringoxygen atomsbenzoxazole -2-thiolGold Surfacespseudosymmetric attachmentN atomsmonolayernitrogen atomsnear-edge X-ray absorptionsulfur anchorLow-Band-Gap AreneoxazolethiolatesInfrared spectroscopyBOxS exhibitbenzene ringsstructure spectroscopySelf-Assembled Monolayersanthraceneoxazole -2-thioloxazole ringsorientationinjection layersfilm qualityX-ray photoelectron spectroscopyspectroscopic techniquesband gaps
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