Reflection FTIR Studies of the Conformation of 2,2‘-Bipyridine Adsorbed at the Au(111) Electrode/Electrolyte Interface

Subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) has been employed to study the conformation of 2,2‘-bipyridine (22BPY) adsorbed at the Au(111) electrode surface. In addition, a b initio Hartree−Fock calculations were carried out to calculate the IR spectra for the trans -planar, cis- planar, and twisted conformations both for an isolated 22BPY molecule and for the molecule attached to a gold atom or ion. The spectra for the trans - and the cis -conformations were predicted to be distinctly different. The differences between the predicted spectra and the differences for most structural parameters between the cis- planar conformer and the torsional conformations with a twist of 0° to 40° between the two rings were small. SNIFTIRS spectra with a good signal-to-noise ratio were measured only for those potentials where the 22BPY molecules associate into stacks. Efficient packing into stacks requires a planar or very nearly planar conformation for the 22BPY molecules. For these potentials, the SNIFTIRS spectra provided direct evidence that 22BPY molecules coordinated to the surface gold atoms assume a cis - or nearly cis -conformation.