Columnar organization of stack-assembled trimesic acid on graphene.

The stack-assembly of trimesic acid molecules into a highly organized columnar structure and their adsorption on graphene has been investigated by a DFT-based ab initio calculation method. Trimesic acid (TMA, benzene-1,3,5-tricarboxylic acid) constitutes an interesting building block for intermolecular hydrogen-bonding architecture by creating a strong net dipole moment which favors a symmetric π-stacking of molecular wire. Both the single orientation (syn) and alternating orientation (anti) of two- and three-unit TMA configurations are optimized, and determine that anti or AB pattern TMA wire is energetically more favorable than the syn case. Meanwhile, a decreasing band gap during the formation of the molecular wire proves the presence of delocalized π-electrons over the entire stack-assembly. The adsorption energy for a columnar TMA stack on graphene was found to be roughly less than of a single TMA adsorbed on graphene. The relative contribution of hydrogen bonding to column packing energy showed to be comparative and reasonable, with the energy of a conventional hydrogen bond. The magnitude of the band gap opening appears strongly correlated with the breaking of the symmetry of π-states of graphene by the TMA columnar patterning on the surface. Our results suggest that a stack-assembled molecular could be used to tune and control the electronic properties of graphene.