Magnetic and transport properties of conjugated and cumulated molecules: the π-system enlightens part of the story.

We have investigated the intramolecular magnetic exchange coupling constants (J) for a series of nitronyl nitroxide diradicals connected by a range of linear conjugated and cumulene couplers focusing on the unusual π-interaction properties within the couplers. Distance between radical centers, spin density within the couplers, as well as the dihedral angles between the radical centers and the plane of the coupler influence the strength of magnetic coupling. We also establish that with the increase in the length of the coupler, the strength of magnetic interaction in conjugated and cumulated systems varies in a different way. Transport calculations show that with the increase in chain length, diradicals based on cumulene containing an even number of carbon atoms act as better conductors than cumulenes with an odd number of carbon atoms. It is also observed that with the increase in the length of the conjugated coupler based diradicals, transmission does not vary in a sequential way.