Ionization energy and energy gap structure of MoSI molecular wires: Kelvin probe, ultraviolet photoelectron spectroscopy, and cyclic voltammetry measurements.

The work function W of Mo(6)S(3)I(6) molecular nanowires is determined by Kelvin probe (KP) measurements, UV photoelectron spectroscopy (UPS), and cyclic voltammetry (CV). The values obtained by all three methods agree well, giving W = 4.8 ± 0.1 eV. CV measurements also give a gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of E(g) = 1.2 ± 0.1 eV, in agreement with recent optical measurements, but in disagreement with theoretical calculations, which predict the material to be a metal. The electronic structure of Mo(6)S(3)I(6) suggests use of the material in applications such as bulk heterostructure photovoltaics and transparent electrodes and for molecular electronics devices.

Strong correlations in highly electron-doped Zn(II)-DNA complexes.

We present spectroscopic measurements on the first example of a chemically electron-doped metal-DNA complex. We show that a doping level as high as the stoichiometric limit of one electron per base pair can be achieved. The doped unpaired electrons occupy lowest unoccupied molecular orbital levels of the nucleobases as detected with electron spin resonance and x-ray absorption near edge structure measurements. Delocalization and strong correlations between the unpaired electrons are evident from a temperature-independent spin susceptibility and a microwave conductivity above 100 K.

Hole interactions with molecular vibrations on DNA.

We report on a study of the interactions between holes and molecular vibrations on dry DNA using photoinduced infrared absorption spectroscopy. Laser photoexcited holes are found to have a room-temperature lifetime in excess of tau > 1 ms, clearly indicating the presence of localization. However, from a quantitative model analysis of the frequency shifts of vibrational modes caused by the holes, we find the hole-vibrational coupling constant to be relatively small, lambda approximately 0.2. This interaction leads to a change in the conformational energy of DeltaE0 approximately 0.015 eV, which is too small to cause self-trapping at room temperature. We conclude that, at least in the dry (A) form, DNA is best understood in terms of a double chain of coupled quantum dots arising from the pseudorandom chain sequence of base pairs, in which Anderson localization prevents the formation of a metallic state.

Beltlike C(60)(-) electron spin density distribution in the organic ferromagnet TDAE-C(60).

The observed huge increase in the width of the (3C)NMR spectra of TDAE-C(0 )n the middle of the ferromagnetic phase at 10 K is due to a Jahn-Teller distortion of the C(60 )(-) which becomes visible in view of the resulting changes in the Fermi contact electron-(13)C NMR shifts. The shape of the (13)C spectra allows for a direct determination of the belt-like redistribution of the unpaired electron spin density on the C(60)(-) ions, which is responsible for the relatively high ferromagnetic transition temperature in this purely organic system.