Dynamic NMR studies of a potential chiroptical switch based on dithiocarbamate-iminodithiolane interconversion

[reaction: see text]. Variable temperature NMR spectra of the chiral spiro[(4-N,N-dimethyldithiocarbamato)-(2-N,N-dimethylimino)-1,3-dithiolane-5,9'-xanthene] show complex dynamics including degenerate interconversion of the dithiocarbamate and iminodithiolane groups. The rate of this switching process can be controlled by chemical modification: the analogous spiro[dithiolane-fluorene] derivative shows no interconversion. These novel materials have potential application as molecular switching elements in information storage devices.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

Two connected inverse spectral transforms

We establish a transformation which connects the potentials of the one-dimensional Dirac and Klein-Gordon operators. This transformation links the solutions of the nonlinear evolution equations solvable by means of the two inverse spectral transforms which use the Dirac and Klein-Gordon direct and inverse spectral problems.     

New Thiophene-Pyrrole-Derived Annulenes Containing 6 and 10 Heterocyclic Units

A series of thiophene-pyrrole-derived annulenes containing either 6 (9a-c) or 10 (14a,band 17) heterocyclic units and 2 vinylene bridges have been synthesized from the appropriate dialdehydes or tetraaldehydes by the McMurry coupling reaction. All of these annulenes except 17 contain one or two intramolecular aliphatic chains linking the pyrrole units. Spectroscopic properties of these annulenes show no evidence for overall aromaticity or antiaromaticity, although the nature of the aliphatic bridge has a small but definite effect on the UV-visible spectra and electrochemical properties of the compounds.