We present a first-principles study of hydrogen bonding effect on current-voltage characteristics of molecular junctions.Three model charge-transfer molecules,2'-amino-4,4'-di(ethynylphenyl)-1-benzenethiolate (DEPBT-D),4,4'-di(ethynylphenyl)-2'-nitro-1-benzenethiolate (DEPBT-A),and 2'-amino-4,4'-di(ethynylphenyl)-5'-nitro-1-benzenethiolate (DEPBT-DA),have been examined and compared with the corresponding hydrogen bonded complexes formed with different water molecules.Large differences in current-voltage characteristics are observed for DEPBT-D and DEPBT-A molecules with or without hydrogen bonded waters,while relatively small differences are found for DEPBT-DA.It is predicted that the presence of water clusters can drastically reduce the conductivities of the charge-transfer molecules.The underlying microscopic mechanism has been discussed.
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