(515d) Improved Stability of Functional Low-Density Self Assembled Monolayers On Gold: A Generalized Approach

Self-assembled monolayers are a convenient method for the alteration of surface chemistry and architecture. The development of low density monolayers (LDMs) has enabled an additional level of control over interfacial chemistry, where the lateral spacing of the surface bound functional groups are altered. This packing density directly influences the conformational freedom of surface tethered molecules, where surface interactions with solvents, analytes, and reactants are all modulated. Critically, LDMs on gold are currently limited in both functionality and stability. We report a generalized approach where “click” thiol-yne chemistry enables the formation of click-LDMs with arbitrary tail group chemistry.

We demonstrate click-LDMs through the preparation of carboxyl-terminated LDMs on gold by adsorption of 1,10 decanedithiol on gold and subsequent grafting reaction of 10-undecynoic acid in presence of a photoinitiatior and light. The resulting LDMs are exceptionally stable with respect to time, temperature and solvents. The click-LDMs showed a high charge-transfer resistance suggesting stable structuring of the monolayer’s base, while both symmetric and asymmetric methylene stretching FTIR modes are red shifted from that of densely packed monolayers supporting a decreased ordering of the alkyl chains compared to traditional SAM. These analyses are consistent with the expected densely-packed, stable region of 1,10 decanedithiol near the gold surface and a covalently region of non-crystalline region which interfaces the environment. Contact angle goniometry is consistent with the expected intermediate surface energy of exposed carboxyl and methylene functionalities. The specificity of the click chemistry enables the examination a large library of functionalities.