Applications of bis(imino)acenaphthene and investigation of boron arsenide as a high thermal conductivity material



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Abstract: Functionalization of the ubiquitous bis(imino)acenaphthene ligand class has been explored. The successful functionalization of this ligand type was found to be dependent upon the steric congestion encompassing the N-C-C-N fragment of the aryl substituted BIAN ligand. The sterically directed functionalization was found to proceed via either a radical backbone dearomatization route or a nucleophilic imine C-alkylation pathway. The structures of each of the functionalized BIAN derivatives were examined by means of single crystal X-ray crystallography. The foregoing reactions were also probed by EPR spectroscopy and DFT-D calculations in order to help elucidate the nature of the driving forces that are involved in BIAN functionalization. A series of aryl substituted BIAN zinc(II) chloride complexes were also prepared and their photophysical properties were investigated. Initially, four different methylated aryl substituents were examined, namely the 4-methylphenyl, 3,5-dimethylphenyl, 2,4,6-trimethylphenyl, and 2-methylphenyl derivatives. Examination of these four complexes revealed them to be non-emissive in solution. However, it was also determined that the 4-methylphenyl and 3,5-dimethylphenyl substituted complexes were emissive in the solid state. On the other hand, the 2,4,6-trimethylphenyl, and 2-methylphenyl complexes were found to be non-emissive in the solid state. The origins of the emissions of the foregoing complexes were also probed by means of TD-DFT calculations. The tuning of the stereoelectronic properties of a series of para-substituted aryl BIAN zinc(II) chloride complexes was undertaken with the view to modifying their solid state photophysical properties. For example, changing the electronic properties of the flanking para-substituted aryl substituents permitted tunability within the range of the red-orange-yellow emissions. Tunability was also achieved by employing a variety of different recrystallization techniques for growing the various structures, polymorphs, and solvatomorphs of each BIAN zinc(II) chloride complex. Boron arsenide, a somewhat neglected semiconductor compound, has been examined for its potential use as a high thermal conductivity material. High quality single crystal BAs microstructures have been synthesized and characterized by means of powder X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and scanning electron microscopy. The thermal conductivity properties of the BAs microstructures have been probed using microheater devices.