Triptycene-Based Tripodal Self-Assembled Monolayer on Indium Tin Oxide

Abstract

The monomolecular assembly of 1,8,13-tricarboxytriptycene (Trip-CA) on a test oxide substrate, represented by indium tin oxide (ITO), was studied. For this purpose, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, contact angle goniometry, and work function measurements were used. The quality and the parameters of the resulting self-assembled monolayers (SAMs) were found to depend strongly on the preparation conditions, with an elevated preparation temperature (50 °C) and post-annealing at an optimal temperature (100 °C) being the most favorable factors. Analysis of the data favors a monodentate bonding configuration for individual CA groups of Trip-CA and a tripodal bonding mode for the molecules as a whole, even though a certain heterogeneity of bonding configurations cannot be excluded. The molecules exhibit a moderate orientational order with an average tilt angle of 32.5°. Because of the nonpolar character of the triptycene backbone, the decoration of ITO with Trip-CA does not result in a significant change of the work function, which speaks for the introduction of polar tail groups at the application of this platform to electrostatic interface engineering.