Electronic Supplementary Information for Transition voltage spec- troscopy reveals significant solvent effects on molecular transport and settles an important issue in bipyridine-based junctions

The theoretical results reported in the present study have been obtained by quantum-chemical calculations performed with the Gaussian 09 package1 at density functional theory (DFT) level by using the B3LYP hybrid exchange functional. Basis sets of double-zeta quality augmented with diffuse functions (Dunning aug-cc-pVDZ) for the light atoms (C, N, H) and with relativistic core potential for gold (cc-pVDZ-PP2) have been employed. Geometry optimizations and single-point calculations for electron affinities (A’s) can be straightforwardly performed in standard DFT Gaussian 09 runs. Bond metric data and total energies for the relevant optimized geometries of the (4,4′)bipyridine molecule are collected in Table S1. The quantity δE0 = Esol 0 −E0 0 can be obtained via standard quantum chemical methods because it requires the knowledge of the LUMO energies E 0 of an isolated molecule, that is, a molecule uncoupled to electrodes. Still, as is well known, the Kohn-Sham “orbitals” do not represent true molecular orbitals, and this particularly applies to the LUMO. Therefore, the LUMO energies have been estimated within ∆-DFT calculations from the lowest electron affinity levels, E 0 =−A0,sol (“Koopmans theorem”), and thence δE0 =−δA.