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.     

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.     

Measurement of the zeta potential of planar solid surfaces by means of a rotating disk

A method for measuring the zeta potential of disks is described. Combining the hydrodynamic properties of a rotating disk, the solution of Laplace's equation for the potential, and the electrokinetic boundary condition, one obtains an equation that relates the zeta potential of the disk to the streaming potential in the disk's vicinity. Theory predicts a dependence of the streaming potential on the rotation rate raised to the 3/2 power. Theory also shows that placement of one reference electrode on the axis of rotation near the disk surface and the other far from the disk is favorable. Measurement of the streaming potential of silicon oxide and indium tin oxide in contact with a solution of potassium chloride demonstrated the expected 3/2 power dependence on rotation rate. The zeta potentials calculated from the combination of the theory and experimental data agreed with published values.     

Introducing variable cell shape methods in field theory simulations of polymers

We propose a new method for carrying out field-theoretic simulations of polymer systems under conditions of prescribed external stress, allowing for shape changes in the simulation box. A compact expression for the deviatoric stress tensor is derived in terms of the chain propagator, and it is used to monitor changes in the box shape according to a simple relaxation scheme. The method allows fully relaxed, stress free configurations to be obtained even in nontrivial morphologies, and it enables the study of morphology transitions induced by external stresses.