Temperature-Induced Structural Phase Transitions in Self-Assembled Hydrogen Bonded Networks at the Liquid/Solid Interface

The effect of temperature on the transformations of hydrogen-bonded structures of trimesic acid (TMA) and p-terphenyl-3,5,3'',5''-tetracarboxylic acid (TPTC) has been investigated at the nonanoic acid/highly oriented pyrolytic graphite (HOPG) interface by scanning tunneling microscopy (STM). STM observations show that TMA assembly based on temperature modulations underwent phase transitions from a chicken-wire (25 degrees C) to a flower (60 degrees C) and further to a guest-host flower structure. Similarly, TPTC network with five kinds of pores underwent change of structural conformation after annealing to 85 degrees C. This work provides a way toward controlled assembly directed by temperature and is beneficial for the understanding of both the assembling process and the underlying kinetics and thermodynamics for molecular nanostructures.