Synthesis, characterization and charge transport properties of metal complexes


Student thesis: Doctoral Thesis

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  • Xiongbo YANG


Awarding Institution
Award date2 Oct 2013


In recent years, synthesis of functional molecular based materials has attracted huge interest not only for fundamental reasons but also for application in semiconductor devices. Among them, metal complexes are most interesting components for their diverse tunable properties. Herein, a series of nickel dithiolene complexes and group 10 metal Schiff base complexes have been synthesized and characterized. The charge carrier transport properties of these materials have been analyzed and a structural property relationship has been established. We anticipate that these materials could be potentially used in organic semiconductor devices. A new series of [Ni(qdt)2]2- ionic complexes with cations as mono-n-alkylated 4,4'-bipyridine (C1-n) have been designed and synthesized. The influence on molecular packing with alkyl chain of different lengths has been investigated by single crystal, grazing incidence X-ray diffraction (GIXRD), structure morphology (scanning electron microscopy techniques) analysis and selected area electron diffraction (SAED). From the crystal X-ray structure analysis, the chain lengths of n-alkyl substituents of the cations have great impact on the molecular packing of their respective crystal structures. The complexes self-assembled to form microstructures through solvent evaporation. The microstructures displayed different morphologies possessing high crystallinity, which represents their lamellar superstructures. A bottom-contact FET (field effect transistor) device is used to analyze the charge transport properties of these microstructures. A series of [Ni(qdt)2]2- complexes with cations as bis(n-alky) - 4,4'-bipyridine (C2-n) have been designed and synthesized. The molecules are packed as a layer by layer structure with π-π interactions existing between the cations and anions. The compounds self-assembled to form microstructures. Microstructures with different morphology were formed due to different length of alkyl chains. Characterization tools such as GIXRD and SAED have been used to understand their well-ordered molecular packing. A bottom-contact FET device is used to analyze the charge transport properties of these microstructures. The results reveal that some complexes (n<10) exhibit p type semiconductor properties due to the π-π interactions and high crystallinity. A series of neutral nickel(II), palladium(II) and platinum(II) complexes of bis((1H-pyrrol-2-yl)methylene)benzene-1,2-diamine (MPy) and bis((1H-pyrrol-2-yl)methylene)-4,5-dimethylbenzene-1,2-diamine (MMePy) have been synthesized and characterized. The charge transport properties of the as-deposited thin films using a bottom contact FET configuration haven been examined, revealing hole mobilities in the range of 3.7×10-7 to 1.1×10-5 cm2/Vs. Using X-ray single-crystal structures and grazing incidence X-ray diffraction data (GIXRD), we have examined the effects of peripheral alkyl substituent(s) and metal ion on the film morphology and charge transport property. Both packing of molecules and film morphology (continuity and crystal grain) are important parameters in determining the overall charge transport properties of organic field-effect transistors. A bottom-contact transistor made from as-deposited NiMePy film exhibited a charge mobility up to 1.1×10-5 cm2/Vs.

    Research areas

  • Charge transfer, Metal complexes, Electric properties