Controlling Self-Assembly of Switchable Azobenzene Derivatives on Highly Oriented Pyrolytic Graphite at Ambient Conditions

Abstract

Ultrathin films prepared at the solid/air interface of azobenzene (AB), 4-(phenylazo) benzoic acid (PABA), 3,4′-azodibenzoic acid (meta-ADB), and 4,4′-azodibenzoic acid (para-ADB) have been studied on highly oriented pyrolytic graphite using scanning tunneling microscopy (STM) and atomic force microscopy (AFM). While AB molecules form compact herringbone pattern stabilized via van der Waals interaction, AB derivatives with carboxyl groups show patterns formed through strong dimeric hydrogen bonds. Depending on the numbers and the positions of carboxyl group(s), we show that the assembly can be controlled at a global level. Due to the right balance of weak and strong intermolecular interactions, PABA molecules show a unique growth at global levels. meta/para-ADB molecules form chains stabilized through carboxyl groups; however, possible adsorption-induced isomers influence the growth behavior and restrict it to limited size on the surface.