Functional molecular wires are essential for the development of molecular electronics Charge transport through molecules occurs primarily by means of two mechanisms, coherent superexchange and incoherent charge hopping Rates of charge transport through molecules in which superexchange dominates decrease approximately exponentially with distance, which precludes using these molecules as effective molecular wires In contrast, charge transport rates through molecules in which incoherent charge hopping prevails should display nearly distance independent, wirelike behavior We are now able to determine how each mechanism contributes to the overall charge transport characteristics of a donor−bridge−acceptor (D−B−A) system, where D = phenothiazine (PTZ), B = p-oligophenylene, and A = perylene-3,4:9,10-bis(dicarboximide) (PDI), by measuring the interaction between two unpaired spins within the system's charge separated state via magnetic field effects on the yield of radical pair and triplet recombination product

Making a molecular wire: charge and spin transport through para-phenylene oligomers.

Magnetic field effects on emission and current in Alq3-based electroluminescent diodes

Magnetic hyperfine modulation of charge photogeneration in solid films of Alq3

In this chapter, we explore experimental and theoretical aspects of molecular wire-like charge transport from the mechanistic point of view. We discuss competition between coherent superexchange and sequential mechanisms of transport through donor-bridge-acceptor systems, where the donor and acceptor are either molecules or metal/semiconductor contacts. The focus is on the two major determinants of mechanism: electronic coupling and energy level matching. Some methods of calculating conductance are outlined, and the relationship between conductance in a metal/molecule/metal junction and electron transfer, where donor and acceptor have relatively discrete electronic energy levels is explored. Finally, we give several examples of chemical systems that have displayed wire-like behavior and discuss their characterization.

Molecules as wires: Molecule-assisted movement of charge and energy

The electrophosphorescence (EPH) efficiency was found to increase by up to 6% for the devices based on a metallo-organic phosphor of iridium and 2% for those based on a metal-organic complex of platinum as an external magnetic field increased to $500\phantom{\rule{0.3em}{0ex}}\mathrm{mT}$. Also, a difference in the field dependence of the EPH for these devices has been observed. We demonstrate that these experimental findings can principally be understood in terms of the Zeeman and hyperfine interactions of electrons located on phosphor molecules and holes located on the hole-transporting molecules, forming correlated electron-hole pairs in the emitting layer. The difference in the field behavior of the effect for the two phosphors results from their different molecular structures.

Magnetic field effects on organic electrophosphorescence

Experimentally observed temperature-dependent shifts in magnetic-field-dependent reaction yield spectra of polymethylene-linked radical ion pairs are correlated with motional shifts in calculated spin-exchange spectra. The compounds investigated are pyrene-(CH{sub 2}){sub n}-N,N-dimethylaniline, n {le} 16, in the polar solvent acetonitrile. Radical ion pairs have been generated by photoinduced intramolecular electron transfer. The magnetic field effect (MFE) was monitored with optical methods: both absorption and emission spectroscopy. The MFE is explained and discussed with the help of qualitative diagrams that provide an integrated picture of the combination of spin dynamics and molecular dynamics. A through-space (solvent) exchange interaction is assumed in our discussions.

Temperature study of the magnetic field effect in photogenerated flexibly-linked radical ion pairs: influence of the stochastically modulated exchange interaction

Hans Gerd Busmann

Papers

Temperature study of the magnetic field effect in photogenerated flexibly-linked radical ion pairs: influence of the stochastically modulated exchange interaction