Complex Structures Resulting from Carboxylic Acid Self-Assembly: Comparison of 2-Naphthoic Acid to Quinaldic Acid and 3-Quinoline Carboxylic Acid

Abstract

Scanning tunneling microscopy was used to study the self-assembly of three molecules on the Au(111) surface: 2-naphthoic acid, quinaldic acid, and 3-quinoline carboxylic acid. All three compounds consist of two fused six-membered rings functionalized at the same position with a carboxylic acid group. Despite their chemical similarity, widely different structures were observed to result from selfassembly after pulse deposition. 2-Naphthoic acid forms cyclically hydrogen-bonded pentamers, a metastable structure that transitions to rows of dimers upon gentle annealing. Quinaldic acid and 3-quinoline carboxylic acid form dimers, tetramers, and hexamers, but no pentamers. Differences in self-assembly between these three compounds are attributed to the ability of quinaldic acid and 3-quinoline carboxylic acid to form zwitterionic species.

Light‐induced Photoswitching of 4‐(Phenylazo)benzoic Acid on Au(111)

“…[34] The non-equilibrium self-assembly that takes place during pulse deposition results in several kinetically trapped, metastable species as opposed to a single thermodynamically favored adsorption state. [25] Studies focused on the self-assembly of carboxylic acids after pulse deposition on Au(111) have observed cyclic hydrogen bonding between the -COOH group andÀ CÀ H groups adjacent to the carbonyl which compensates for the increased OHÀ O bond strain. [25,35] It is possible that some PABA molecules in Figure 3 may be positioned with a tilt to the surface normal due to non-parallel adsorption of the phenyl rings as proposed in prior studies.…”

“…[25] Studies focused on the self-assembly of carboxylic acids after pulse deposition on Au(111) have observed cyclic hydrogen bonding between the -COOH group andÀ CÀ H groups adjacent to the carbonyl which compensates for the increased OHÀ O bond strain. [25,35] It is possible that some PABA molecules in Figure 3 may be positioned with a tilt to the surface normal due to non-parallel adsorption of the phenyl rings as proposed in prior studies. [36] However, providing conclusive evidence for the exact orientations based on STM imaging is difficult.…”

“…[24] During pulse deposition, molecules engage in non-equilibrium selforganization, which produces several kinetically trapped metastable states as opposed to a single thermodynamically favored structure. [25] Herein, this paper reports the photoswitching of 4-(phenylazo)benzoic acid or PABA (Figure 1) deposited on a Au(111) surface via a pulse solenoid valve. The carboxylic group in PABA permits covalent bonding to various precursors via amide/ester linkage and ligand function through deprotonation.…”

“…An advantage of this method is the ability to combine solution‐based chemistry with ultra‐high vacuum (UHV) studies, in which every component present in the sample solution is deposited on an atomically flat substrate [24] . During pulse deposition, molecules engage in non‐equilibrium self‐organization, which produces several kinetically trapped metastable states as opposed to a single thermodynamically favored structure [25] …”

Design and construction of on-surface molecular nanoarchitectures: lessons and trends from trimesic acid and other small carboxlyated building blocks

“…For solution-based studies, where molecules are cast or deposited onto a surface through dip-coating, molecules must be solvated in a suitable solvent, such as methanol [32], toluene [33] or water [34]. The substrates for these studies need to be relatively non-reactive, and tend to be HOPG, graphene or Au(1 1 1), although Buck's group has had a great deal of success with studies on underpotential deposited copper and silver surfaces on Au(1 1 1) (see section 5.1.2) [35][36][37][38][39].…”