Synthesis, characterization and properties of phenalenyl-based neutral radical molecular conductors.

摘要

While organic conductors usually require charge-transfer to generate charge carriers, our approach toward an intrinsic metal uses a single molecular species that would function as a classical (mono)atomic metal and superconductor. This requires the crystallization of neutral radical and phenalenyl (PLY) is our chosen target. Previous work from our group showed that the first biPLY based radical conductor (10) exhibits the highest conductivity (sigmaRT = 0.05 S/cm) of any neutral organic molecule.*;In this thesis, we report on several spiro biPLY radicals with different R groups on nitrogen which have been synthesized, crystallized and characterized, as well as the preparation of precursors that failed to give crystalline radicals. It has been found that solutions of radical 25 (R = Octyl) can give rise to two crystalline forms depending on whether the crystallization is allowed to proceed in the presence or absence of light. In both cases the crystals take the form of black shining blades which are indistinguishable by optical microscopy. The crystalline forms have been fully characterized, and it has been shown that they differ by the presence or absence of a C-C sigma-bond between the unpaired electrons of the parent radical. These molecular forms crystallize from the same solvent to give rise to a sigma-dimerized insulator and a monomeric radical semiconductor with room temperature conductivity (sigma RT = 1x10-5S/cm) as dictated by the presence or absence of light.;Radical 24 (R = Heptyl) is monomeric in the solid state and shows Curie behavior through the temperature range 9-335K, while radical 23 (R = Methyl) forms face-to-face pi-dimers with mean plane separation 3.4 A and shows Curie behavior from room temperature to 33 K at which point antiferromagnetic coupling is observed. Radical 24 exhibits sigma RT = 5x10-4 S/cm, while radical 23 yields small crystals with pressed pellet conductivity measured of sigma RT = 0.8x10-4 S/cm.;Radical 22 (R = H) forms a new type of pi-pi stacked chain, and the structure is best viewed as a compromise of the competition between the hydrogen bonding and the radical pi-pi interaction. Magnetic susceptibility data indicate Curie behaviour above 142 K, while below this temperature there is a hysteretic phase transition which leads to a diamagnetic state; the radical shows a pressed pellet conductivity of sigmaRT = 1.5x10-3 S/cm.;*Please refer to dissertation for diagram.