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.

How far the chemistry of self-assembled monolayers on gold surfaces affects their work function?

“…This confirms that the dipole moment of the molecule plays a role in the final value of the WF. 23 It corresponds to a contribution of −0.1 eV, which is smaller than the contribution of the chain length. This 0.1 eV is in sharp contrast to the values of the electric dipole of the free molecules that were computed to +0.49 D and −5.25 D for ABT and MPA, respectively.…”

“…Tail groups other than CH 3 have also been studied, such as carboxy, alkoxy, amino or thio groups [17][18][19][20] or fluorinated tail groups. [21][22][23] Very active debates have appeared in the literature related to the change of this substituent and the subsequent modulation of the electrostatic properties of metallic surfaces. [24][25][26][27][28] Among these properties, the work function (WF) is the most emblematic one.…”

Phosphonic acid anchored tripodal molecular films on indium tin oxide

“…A promising system in this context is a family of triptycenebased molecules, applied successfully on a variety of substrates. [26][27][28][29][30][31][32][33] The triptycene scaffold consists of three phenyl rings coupled together by an aliphatic linker. It can be flexibly functionalized with suitable anchoring groups at the para-positions of the rings, providing then a good prerequisite for tripodal anchoring.…”

Triptycene-Based Self-Assembled Monolayer as a Template for Successive Click Reactions

“…One of such cases are triptycene-based molecules with thiol and carboxylate anchoring groups, capable to form densely packed and highly ordered SAMs on gold, silver, and oxide substrates. − These molecules feature tripodal bonding to the substrate, which is rarely the case among tripod-shaped adsorbates, − and can host either three tail groups at the tripodal para-positions of the individual phenyl blades or a single tail group at the bridgehead position of the entire scaffold. However, the synthesis of these molecules in each specific case represents a many-step procedure, so that it would be reasonable to look for complementary approaches to create specifically substituted triptycene-based molecular systems as a versatile scaffold for surface modifications.…”