Design, Synthesis And Opto-Electronic Properties Of Conjugated Coordination Compounds

Coordination compounds possess both characteristics of inorganic compounds and organic compounds. Due to the flexible electronic structures, easily accessible electron delocalizations and diversified opto-electronic properties of conjugated coordination compounds, they have been extensively used in such fields as organic light-emitting diodes (OLED), organic solar cells (OSC), organic field-effect transistors (OFET), organic nonlinear optics, sensors and so on. Nevertheless, the research on coordination compounds has been much less compared with organic molecules, leaving many issues. Therefore, the research and development on opto-electronic materials of conjugated coordination compounds has attracted more and more attentions in the past decades, being a challenging work. In this thesis, a series of planar Metal Salen Complexes, Metal Dithiolene Complexes (including Nickel Dithiolene Complexes with planar structures and Molybdenum Tris-Dithiolene Complexes with three dimensional structures) and planar Platinum Diimine Complexes (including small molecules and polymers) were designed and synthesized. Their opto-electronic properties (mainly including charge transport properties and two-photon absorption properties) were studied, and the relationships between structure and property were summarized. Device fabrications and applications of some complexes were also explored.The main contents of this thesis are described as following:Chapter1is the introduction of the whole thesis. At first, the basic concept, structural features and potential applications of conjugated coordination compounds with opto-electronic activities were presented. Then the background and key structure-property relationships of organic charge transport materials and organic two-photon absorption materials were briefly summarized, and recent progress and development of coordination compounds in these two fields were also reviewed.In Chapter2, four planar Metal Salen Complexes (M=Ni or Cu) were designed and synthesized, and their structures were characterized by nuclear magnetic resonance (NMR), mass spectra (MS), elemental analysis (EA), etc. Their basic physicochemical properties were studied by thermogravimetric analysis (TGA), UV-Vis absorption spectra and cyclic voltammograms (CV). Time of flight (TOF) technique was used to investigate their charge transport properties, and the results indicated that Ⅱ-1a and Ⅱ-1b showed hole transport properties while Ⅱ-2and Ⅱ-3exhibited balanced ambipolar charge transport properties. Ⅱ-3showed the highest mobilities to10-5cm2/Vs for both holes and electrons, suggesting a new candidate of ambipolar charge transport materials. X-ray powder diffraction (XRD) and atomic force microscopy (AFM) were carried out to study their thin film morphologies, demonstrated high crystallinity of the vacuum deposited film of Ⅱ-3. Theoretical calculations on their optimized structures and electron-state-density distribution of their frontier orbitals were taken and the results provided an explanation for their differences in charge transport behaviors.In Chapter3, three planar Nickel Dithiolene Complexes were synthesized, and their structures were characterized by NMR, MS, EA, etc. UV-Vis-NIR absorption spectra and CV results revealed that these complexes possess very low LUMO levels and stable electrochemical processes, implying that they might be a kind of air stable n-type semiconductors. Theoretical calculations were used to predict their optimized structures and electron-state-density distribution of their frontier orbitals, and further calculated their reorganization energies. OFET devices of these complexes were fabricated to investigate their charge transport properties. Ⅲ-3exhibited excellent n-type OFET performance with highest mobility to0.11cm2/Vs and on/off ratio to2×106on PS-SiO2substrate (deposition at70℃). XRD and AFM were taken to study their thin film morphologies, and investigate the influences of film morphology structures on OFET properties.In Chapter4, two Molybdenum Tris(Dithiolene) Complexes were designed and synthesized, and their structures were characterized by NMR, MS, EA, etc. UV-Vis-NIR absorption spectra, CV results as well as theoretical calculations demonstrated that these complexes have very low LUMO levels and broad UV-Vis-NIR absorption features, implying that they might be a kind of n-type semiconductors with potential applications for OSC. TOF technique was used to investigate their charge transport properties. It was found that these two complexes exhibited weak electron transport responses, and for IV-2, the electron mobility of10-6cm2/Vs can be detected, indicating a new electron transport compound with three dimensional structure and solution processability. These two compounds were also selected as acceptors blended with poly(3-hexylthiophene) to fabricate OSC devices. Unfortunately, primarily results showed no photovoltaic property, and the possible reason was roughly discussed.On the basis of above work in Chapter3and4, four Molybdenum Tris(Dithiolene) Complexes were synthesized In Chapter5, and their structures were characterized by NMR, MS, EA, etc. The third order nonlinear optical properties of V-1and V-2were investigated by z-scan technique using femto-second laser, and two-photon absorption (TPA) responses were observed at around1300nm. In addition, pico-second laser z-scan technique was used to investigate the nonlinear absorption properties of all six Molybdenum Dithiolene Complexes synthesized in Chapter4and5, and the structure-property relationship of these compounds was summarized. These results indicated that this class of compounds was a new TPA chromophore at telecommunications wavelengths.In Chapter6, two arylalkyne ligands (D-π-D’ and D-π-A type) and four corresponding planar Platinum Diimine Diacetylides were designed and synthesized, and their structures were characterized by NMR, MS, EA, etc. Their single-photon photophysical properties were studied by UV-Vis absorption spectra and fluorescence spectra. Their TPA properties were investigated by two-photon induced fluorescence (TPIF) technique (for fluorescent compounds) with femto-second laser or z-scan technique with pico-second laser (for non-fluorescent compounds), respectively. The results demonstrated that Ⅵ-4displayed orange-red fluorescence with relatively high fluorescence quantum yield and strong TPA cross-section, implying its potential application for two-photon laser scanning microscopy. Their optimized structures and electron-state-density distribution of frontier orbitals were investigated by theoretical calculations.In Chapter7, four A-π-D-π-A type molecules end-capped with pyridine were designed and synthesized, and their structures were characterized by NMR, MS, EA, etc. Three Platinum coordinated polymers based on above molecules were also synthesized, which were characterized by NMR, EA, TGA and gel permeation chromatography (GPC). These results demonstrated that Ⅶ-P2and Ⅶ-P3have large molecular weight and high thermal stability. Their single-photon photophysical properties were studied by UV-Vis absorption spectra and fluorescence spectra, and their TPA properties were investigated by fetmo-second TPIF technique. The influences of donor structures and Platinum coordination on one-and two-photon properties were discussed in details. AFM results showed that Ⅶ-P2and Ⅶ-P3have good film-forming properties.