title: Multi-point Hydrogen-Bonded Organic Cocrystals for Optoelectronic Materials: Design, Synthesis and Characterization
Creators: name: Zhou, Ruixue
Publisher: name: University of Liverpool Repository
Year: 2028

description: The enormous global demands for low-cost, ease-of-use, light-weighted and flexible organic semiconductors have continued to drive the research. Organic cocrystal engineering, one of the methodologies to design new organic materials with unconventional functionality, has attracted great attention globally. Organic cocrystal engineering, taking advantage of organic synthesis, the self-assembly of molecules, and the great chemical versatility of organic compounds, offers an excellent option to tap the full potential of organic and organo-metallic compounds to address diverse demands and challenges. Cocrystal series, DBA-M(L), including DBA-3, Ni(L1)2·4DBA, and PdLN2C8-DBA etc., and M(L)-NDIs, including Ni(L1)2-NDIC8H, Pd(L1)2-NDIC8H, and Zn(L1)2-NDIC8H, were designed, synthesized and characterized by using SCXRD, NMR, IR, UV-vis, TGA, and XPS techniques. The cocrystal complexes, built by components DBA, M(L) and NDI and their derivatives, were designed, synthesized and characterized using NMR, XRD, IR, UV-vis, TGA, and XPS techniques. The materials were applied in OFETs, and the electronic properties were studied. Most cocrystals showed improved electronic properties, compared to the corresponding single components. The crystal packings, structure-property relationships, and self-assembling process were discussed, supported by the combination of single crystal structure study, crystal structure stimulation and the calculations of the electronic structures. This work involves the theories of inorganic chemistry, crystallography, organic semiconductors, optoelectronic devices, and supramolecular chemistry. Chapter 1 introduced the concepts and the theories of organic semiconductors, supramolecular chemistry and crystal engineering and their applications, as well as the structure and applications of optoelectronic devices, including OFET, SCFET and TFT. Chapter 2 covers the experimental part of my research. In Chapter 3, the polymorphism of DBA was studied, which covered the study of crystal structure and the electronic property of three polymorphs of DBA, i.e. DBA, DBA·3H2O and DBA·3.5H2O. The asymmetric mobilities of the single crystals were observed for DBA-3. In the structure, the closest distance of the π-π stacking was found to be 3.309 Å, which falls in the range of suitable distances for charge transfer and the mobility of DBA·3H2O was found to be 0.032 cm2 V-1 s-1. The variation of the hydrogen bonding structures in the three polymorphs contributes to the different ways of packing DBA molecules in the crystals or the polymorphism. In Chapter 4, a series of guanines and biguanides, their complexes with transition metals M-L, M = Co(II), Ni(II), Cu(II), Zn(II) and Pd(II) were designed, synthesized and characterized using SCXRD, NMR, IR, UV-vis, TGA, and XPS techniques. Ni(L1)2·4DBA was first designed and synthesized as a tetra hydrogen bonded model. Pd(LN2C8)-DBA was then developed to improve the solubility and film-forming properties of the model. With LN2C8 as the ligand, where a substitute group is an n-octyl group, the materials showed high flexibility. And, flexible OFET devices were thus achieved using M(LN2C8) complexes and their cocrystals. Meanwhile, the cocrystals showed more stable electronic properties than the single metal-ligand complexes, and better performance in TFT was observed, compared to the corresponding single components. In Chapter 5, cocrystal Ni(L1)2-NDIC8H was designed, synthesized and characterized. The asymmetric NDI derivative, NDIC8H, was successfully synthesized from NDA, with good yield, and its cocrystal with Ni(L1)2 was obtained. The asymmetric NDIC8H was applied, and enhanced optic and electronic properties were achieved. The findings from this research could contribute to the design of new optoelectronic functional materials.