Trimesic acid is a kind of important chemical raw material. It is made up of a benzene ring with three carboxylic groups at the 1, 3, and 5 positions, and it can be synthesized from the oxidation of 1,3,5-trimethyl benzene. Trimesic acid can in principle form two-dimensional hydrogen-bonded hexagonal networks in which central holes of the network have net diameters of 14. Although such holes would be expected to be natural locations for guest molecules, non-catenated single networks have not been found in any of the crystals containing TMA studied in the last sixteen years. The applications of trimesic acid can be found in the industry of epoxy curing agent, adhesives and coating material, engineering plastic, synthetic fiber, cross-linking agent for alkyd resin, plasticizer, pharmaceutical and other organic compound. Trimesic acid is a prototype molecule to study 2D self-assembly on surfaces via hydrogen bonds. Two polymorphs are usually observed both in Ultra High Vacuum (UHV) and at liquid-solid interface: the honeycomb structure (top left) and the flower structure (top right).