Towards the development of organic magnetoconducting materials: structural, magnetic and conducting properties of diaryl-1,2,4-benzotriazinyl radicals and polyradicals

Date

2011-05-31

Authors

Yan, Bin

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Abstract

Considerable interest exists in the development of purely organic magneto-conducting materials for spintronics. Towards this end, an investigation of the effect of electronic structure, magnetic exchange, and electrical conductivity on the properties of open-shell delocalized organic conjugated polymers was carried out. The design, synthesis and properties of radical-based multifunctional magnetic materials have been developed in which (i) a series of functionalized benzotriazinyl radicals have been synthesized and characterized, (ii) a series of benzotriazinyl alternating copolymers with vinyl and heteroaromatic bridges have been prepared and characterized, and (iii) the magnetic properties of the resulting polymers have been investigated as a function of doping state in order to probe relationships between magnetic and electrical properties of these systems. New synthetic methodology -has been developed which allows the syntheses of 1,3-diphenyl-l,2,4-benzotriazinyl (DPBT) radicals and derivatives under mild reaction conditions. The condensation of arylamines with chlorohydrazones followed by reductive or oxidative ring closure allows generation of the desired radicals. The series of DPBT radicals prepared were found to be thermally and chemically stable in both the solid and solution states. The radicals were spectroscopically characterized by mass spectrometry, EPR, electrochemistry, UV-Vis, electronic absorption spectroscopy, X-ray crystallography, and magnetometry. Single crystal X-ray diffraction studies indicate that these radicals exhibit [pi]-stacking interactions in the solid state which lead to unusually strong anti ferro- or ferromagnetic exchange interactions. Cyclic voltammetry experiments reveal that these radicals exhibit unusually low oxidation potentials, leading to an important class of spin-polarized donors for multifunctional magnetic materials. A new class of DPBT containing alternating copolymers with varying connectivity, bridge structure, and redox activity has been prepared by metal-catalyzed cross coupling. All of the polymers were spectroscopically characterized by EPR, cyclic voltammetry. electronic absorption spectroscopy, and magnetometry. The relationship between magnetic exchange and electrical conductivity was studied as a function of redox state (chemical doping). Preliminary results suggest that there is a correlation between magnetic property and electrical conductivity. As a result, a purely organic ferromagnetic semiconductor critical for investigations in organic spintronic materials was designed and synthesized. Lastly, a new triazinyl donor-acceptor dyad was designed and synthesized. Spectroscopic investigation of electronic and magnetic properties reveal that this radical exhibits an intramolecular - charge-transfer band and strong intermolecular antiferromagnetic interactions.

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Keywords

spintronics, polymers

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