Scanning tunneling microscopy and local conductance mapping show spin-state coexistence in bilayer films of Fe[(H2Bpz2)2bpy] on Au(111) that is independent of temperature between 131 and 300 K. This modification of bulk behavior is attributed in part to the unique packing constraints of the bilayer film that promote deviations from bulk behavior. The local density of states measured for different spin states shows that high-spin molecules have a smaller transport gap than low-spin molecules and are in agreement with density functional theory calculations.

The preparation and characterization of three new donor-bridge-acceptor biradical complexes are described. Using variable-temperature magnetic susceptibility, EPR hyperfine coupling constants, and the results of X-ray crystal structures, we evaluate both exchange and electronic couplings as a function of bridge length for two quintessential molecular bridges: oligo(para-phenylene), β = 0.39 Å(-1) and oligo(2,5-thiophene), β = 0.22 Å(-1). This report represents the first direct comparison of exchange/electronic couplings and distance attenuation parameters (β) for these bridges. The work provides a direct measurement of superexchange contributions to β, with no contribution from incoherent hopping. The different β values determined for oligo(para-phenylene) and oligo(2,5-thiophene) are due primarily to the D-B energy gap, Δ, rather than bridge-bridge electronic couplings, H(BB). This is supported by the fact that the H(BB) values extracted from the experimental data for oligo(para-phenylene) (H(BB) = 11,400 cm(-1)) and oligo(2,5-thiophene) (12,300 cm(-1)) differ by <10%. The results presented here offer unique insight into the intrinsic molecular factors that govern H(DA) and β, which are important for understanding the electronic origin of electron transfer and electron transport mediated by molecular bridges.

Multiple randomized, multicenter trials have established the role of the implantable cardioverter-defibrillator (ICD) in the treatment and prevention of sudden cardiac death. However, transvenous ICD leads have significant short- and long-term complications, offsetting some of the benefit of this therapy. This has led to the development of the entirely subcutaneous ICD. This system is safe and effective, avoiding the need for intravascular leads. It is best suited for patients at low risk for pacing and increased risk for transvenous lead complications. Ongoing randomized and long-term registries will help identify the optimal role of this device in clinical practice.

Using first principles calculations, we predict a complex multifunctional behavior in cobalt bis(dioxolene) valence tautomeric compounds. Molecular spin-state switching is shown to dramatically alter electronic properties and corresponding transport properties. This spin state dependence has been demonstrated for technologically relevant coordination polymers of valence tautomers as well as for novel conjugated polymers with valence tautomeric functionalization. As a result, these materials are proposed as promising candidates for spintronic devices that can couple magnetic bistability with novel electrical and spin conduction properties. Our findings pave the way to the fundamental understanding and future design of active multifunctional organic materials for spintronics applications. ■ INTRODUCTIONMolecular spintronics seeks to exploit the electronic structural diversity of molecules to harness the spin of the electron in novel and improved computing and information storage applications. 1−4 Significant material focus in this area has been placed on the class of conjugated organic semiconductors (e.g., rubrene and tris(hydroxyquinolato)-aluminum) that have found applications in organic optoelectronics devices. 5 These materials, while often diamagnetic, have been reported to show dramatic spin-dependent charge transport effects including giant magnetoresistance (GMR) 6,7 and tunneling magnetoresistance (TMR). 8−10 However, recent years have seen net advances in the use of novel molecular materials synthesized for specific spin properties. This includes design and applications of single molecular magnets, which can have large spin quantum numbers and can be integrated into thin films 11−13 suitable for device applications. 14,15 In addition, the conjugated ferrimagnetic coordination polymer V(TCNE)x 16 has very recently been employed as a thin film electrode in an all-organic TMR-based spin valve device. 17 A molecular design motif with significant promise for spintronics is the spin crossover phenomenon 18 in which a transition between high-spin and low-spin states of a coordination compound can be externally tuned by temperature, light, or applied pressure. This is very common in a number of Fe(II) compounds with nitrogen-containing ligands and has been suggested for many years as a route to molecular memory devices due to the prevalence of hysteretic effects in the spin transition. 19 Recently, both experiment 20 and theory 21,22 have suggested spin state dependence of electrical transport in Fe(II) spin crossover compounds making them prime candidates for molecular spintronics.A chemical elaboration of the spin crossover phenomenon can be established through the use of radical dioxolene ligands complexed to a cobalt coordination center in a class of compounds called valence tautomers (VTs). 23,24 In valence tautomers, a high-spin to low-spin transition on the Co is accompanied by an intramolecular electron transfer from the Co to a redox active ligand.This suggests a very dramatic coupling betwee...

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