Phenylboronic Ester- and Phenylboronic Acid-Terminated Alkanethiols on Gold Surfaces

In this work, it is shown that a well-organized monolayer of phenylboronic ester-terminated thiol (BOR-capped) on gold surfaces can be prepared. Our results also show that the BOR-capped molecular system can be cleaved directly on the surface, resulting in an unprotected BOR-uncapped monolayer with the boronic acid functional groups available for coordination to diol molecules in the ambient media. The monolayers of BOR-capped and BOR-uncapped were characterized using infrared spectroscopy, near edge X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, ellipsometry, and contact angle goniometry. The X-ray photoelectron spectroscopy results showed that both BOR-capped and BOR-uncapped are chemically linked to the gold substrate. According to the infrared spectroscopy results, the main component of the C═O vibrational mode present in the amide moiety is perpendicular oriented relative to the gold surface normal for the BOR-capped molecular system. The near edge X-ray absorption fine structure spectroscopy resonance peak located at approximately 285 eV, assigned to π 1 * transitions, was used to estimate the average tilt angle of the vector parallel to the π* orbitals of the aromatic ring relative to the gold surface normal. The average tilt angle is estimated to be approximately 63° for the BOR-capped monolayer on gold surfaces. The aromatic ring of the BOR-uncapped molecule has a more tilted orientation compared to the BOR-capped one. The experimental infrared spectroscopy and near edge X-ray absorption fine structure spectroscopy results were supported with theoretical modeling including calculations of vibrational modes and of excitation processes.