Ferromagnetic spin alignment in head-to-tail coupled oligo(1, 4-phenyleneethynylene)s and Oligo(1,4-phenylenevinylene)s bearing pendant p-phenylenediamine radical cations

The intramolecular and long-range ferromagnetic coupling between p-phenylenediamine radical cations in head-to-tail coupled oligo(1, 4-phenyleneethynylene)s and oligo(1,4-phenylenvinylene)s between neighbors and next-nearest neighbors is described. UV/vis/near-IR experiments show that the radical cations are localized in the pendant p-phenylenediamine units of the conjugated oligomers. The ESR spectra of these oligo(1,4-phenyleneethynylene) and oligo(1, 4-phenylenvinylene) di(radical cation)s are consistent with those of a triplet state. A linear behavior is observed for the doubly integrated ESR intensity of the DeltaM(s) = +/-1 and DeltaM(s) = +/-2 signals with the inverse temperature (I approximately 1/T), consistent with Curie's law. This behavior indicates a triplet ground-state diradical with a large triplet-singlet energy gap or possibly a degeneracy of singlet and triplet states.     

Full wave electromagnetic simulation of electrooptic high-speed probes

This paper outlines the process of modelling external electrooptic probes mounted on coplanar waveguides (CPW). The techniques used to describe the electromagnetic properties of the external probes are the finite difference time domain (FDTD) method and the finite difference transmission line method (FDTLM). These full wave techniques are time domain in nature that must be Fourier transformed to describe important frequency domain characteristics such as scattering parameters. The optical retardation of the probe is related to the full wave analysis through a commonly used grid size that results in a generalized basis for a complete electrooptic system analysis including a unique definition of an electrooptic transfer function,H(). Following the field simulation, the properties of the probe (invasiveness, retardation, signal distortion and group delay) are presented. Procedures for optimizing models for probe tips are discussed and related to a first-order model that has been developed. The results indicate that these probes can be simulated successfully on moderately sized Unix work stations and that the optimization of probe models must include the full wave simulation in the definition of the necessary gradients for the optimization process.     

Supramolecular phthalocyanine dimers based on the secondary dialkylammonium cation/dibenzo-24-crown-8 recognition motif

[formula: see text] New unsymmetrically substituted DB24C8-phthalocyanines, which are able to form complexes with suitable dialkylammonium cations, have been prepared. These complexes most probably have a pseudorotaxane geometry.