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

摘要

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 metal-molecule 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 metal-molecule-metal systems.