| Perylene tetracarboxylic diimide (PDI) derivatives are important molecular building blocks that are currently being investigated for use in a variety of photoactive organic materials because of their low light and thermal fading rates, high luminescence efficiency, wide absorption and emission bands in visible region, and variable optoelectronic properties. They have been applied in nanoscale field-effect transistors, light-harvesting solar cells, photovoltaic devices, light emitting diodes, and as robust organic dyes that are resistant to photobleaching.Driven by the demands of diverse applications, the modification on molecular structure of PDI aimed at changing the photophysical properties has attracted a lot of research interest in the past decade. However, how to control the properties by modifying on the molecular structure has always been a disturbing problem. In this paper, we designed and synthesis a series of new PDI compounds aimed at modifying their self-assemble process and controlling the structure of the assembly. The structure-property relationship is discussed. The research work of this thesis includes:In chapter1, the research on the synthesis, properties and applications of perylene diimide derivatives have been reviewed. The topic of special photophysical properties of PDI compounds in special media is selected as the focus of this part.In chapter2, perylene tetracarboxylic diimides (PDIs) dimers linked with conjugated chain of different length at the bay positions, namely two alkyne groups, four alkyne groups and two phenylenes, and six alkyne groups and four phenylenes, have been synthesized. Their photophysical properties in room temperature were studied by steady state absorption and emission spectra, the fluorescence quantum yield were calculated. The UV-vis absorption and fluorescence spectra of these three compounds show different concentration-dependent behaviors, which depend on the conjugated chain of different length at the bay positions. Significant aggregation in organic solvents was revealed by the electronic absorption and emission spectra as well as the fluorescence quantum yield calculation. The aggregation behavior of these compounds in the solid state was investigated by X-ray diffraction (XRD), and the morphology of the aggregates was examined by atomic force microscopy (AFM). The aggregation of dimer1with two alkynes at the1and7positions results uniform solid film, whereas dimer2and3with more alkynes and phenylenes at the bay positions formed one-dimensional rod-like aggregates with the aspect ratio of the latter significantly larger than the former. The results of this research revealed that ethynyl and phenyls are suitable linkages to extend the effective conjugation length and enhance π-π interaction. These results will be helpful in guiding the design of new organic molecules for the self-assemble organic functional materials in molecular electronic devices.In chapter3, A soluble binuclear phthalocyaninato copper (Ⅱ) complex, Cu2[Pc(COOC8H17)6]2(1), with planar molecular structure and extended conjugation system, has been designed and synthesized. By fusing two phthalocyanine rings side by side and introducing electron withdrawing groups at periphery positions, the energy levels of HOMO and LUMO have been tuned successfully into the range of an air-stable ambipolar organic semiconductor required as revealed by the electrochemical studies. With the help of a solution-based quasi-Langmuir-Shaer (QLS) method, thin solid films of this compound were fabricated and organic field effect transistors (OFETs) based on these QLS thin solid films were constructed. Because of the promising electrochemical properties as well as the high ordered packing structure of the molecules in the thin solid films, the OFETs performed excellent ambipolar operating properties, with the electron and hole mobility in air as high as1.7X10-1and2.3X10-4cm2V-1s-1, respectively. For comparison purpose, mononuclear compound Cu[Pc(COOC8H17)8](2) was comparatively studied. The QLS thin solid films of this compound possess similar ordered structure with that of Cu2[Pc(COOC8H17)6]2(1), but the OFETs based on the thin solid films of this compound can only show n-type properties under nitrogen atmosphere with an extremely small electron mobility of1.6X10-4cm2V-1s-1. This result suggests that extension on the conjugation system of an aromatic compound with multiple electron withdrawing groups can tune the molecule into an air stable ambipolar organic semiconductor.In chapter4, One perylenetetracarboxylic diimide (PDI) derivatives (PDI1) linked with pyrene by flexible chain at the bay positions was synthesized and the molecular structure was characterized by1H NMR, MALDI-TOF mass spectra as well as elemental analysis. The molecular self-assembly were prepared from solution via a slow evaporation of solvent. The properties of these molecular aggregates were studied by electronic absorption and fluorescence spectra. The morphologies and structures were examined by scanning electronic microscopy (SEM) and X-ray diffraction (XRD) techniques. The conducting properties were evaluated by current-voltage (I-V) measurements. The results revealed highly ordered structure for these molecular self-assembly. The thin solid film fabricated from these molecular self-assembly show an electric conductivity as high as4.85×10-4S cm-1under the ambient light, which means this compound might be used as a semiconductor in nano-electronics. |
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