Packing of Isophthalate Tetracarboxylic Acids on Au(111): Rows and Disordered Herringbone Structures

ABSTRACT: Scanning tunnelling microscopy (STM) has been used to investigate the formation of hydrogen-bonded structures of the isophthalate tetracarboxylic acids, biphenyl-3,3′,5,5′-tetracarboxylic acid (BPTC), terphenyl-3,3″,5,5″-tetracarboxylic acid (TPTC), and quarterphenyl-3,3‴,5,5‴-tetracarboxylic acid (QPTC), via deposition from solution onto Au(111). STM data reveal that ordered structures can be formed from an aqueous solution leading to the formation of rows for the shortest acid BPTC, while the longer molecules TPTC and QPTC adopt a herringbone-like structure with significant degrees of disorder. The influence of solvent and substrate on the molecular ordering is discussed, and density functional theory is used to identify molecular models for these new phases. Carboxylic acids constitute a group of organic molecules which have been extensively explored in surface science and have provided, through studies of the adsorption of trimesic acid o