Adsorption of polyfunctional 5-fluorouracil and 2,4-dithio-5-fluorouracil on Au(111) surface: Structure, energy, and electronic transmission

Adsorption of 5-fluorouracil (5-FU) and 2,4-dithio-5-fluorouracil (2,4-DT-5-FU) on Au(111) surface at low coverage is studied by using periodic-slab-density functional theory calculation. Isolated 5-FU molecule adsorbs preferentially at bridge site in a vertical configuration via N?H group by forming the N?H...Au nonconventional H-bond. The formation of the anchor Au?O bond is not observed. Substitution of oxygen atoms of 5-FU with sulfur strongly influences the nature of adsorption and leads to the Au?S anchor bond and the N?H...Au nonconventional H-bond of single 2,4-DT-5-FU molecule on Au(111) surface. The adsorption site and orientation of 2,4-DT-5-FU molecule on the surface are similar to those of 5-FU. The metalmolecule coupling effects at asymmetric Au/S(N?H)S/mol/C?H/Au and Au/N?H/mol/O/Au transport junctions and symmetric Au/S(N?H)S/mol/mol/S(N?H)S/Au and Au/O/mol/mol/O/Au transport junctions are also investigated. The electronic structure is analyzed in detail, and the obtained results are used for illustrating the electron transmission in metalmoleculemetal systems. (c) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011