Self-Assembled Monolayers of Pseudo-C2v-Symmetric, Low-Band-Gap Areneoxazolethiolates on Gold Surfaces

A 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 exhibi...