Design, Synthesis And Aggregation Properties Of Perylene Tetracarboxylic Diimide Derivatives With Long Alkyl Chains

Self-assembled π-conjugated systems have attracted tremendous attention in the past years owing to their potential application in organic electronics. Numerous functional π systems molecules, for example, perylenetetracarboxylic diimide (PDI), porphyrins, phthalocyanines and so on have been intensively investigated aiming to their application as organic photoconductors, semiconductors, solar energy conversion, liquid crystal materials, biological fluorescent probes and solar cells and so on.In recent years, emphasis has been given on the organization of tailored functional π systems by self-assembly leading to one-dimensional stacks of π-π aggregates in solution, in organogels, and in columnar liquid crystalline (LC) phases. Driven by the demands of diverse applications, the modification on molecular structure of PDI aimed at changing the photophysical properties is one of the most active fields of PDI studies. How to find a structure with novel properties has always been a problem in this area. In this paper, in order to find the relationship between structure and properties of PDIs, we introduced some functional groups to the PDI compounds, endowed these molecules with some special functions and studied their influence on the properties. The content of this thesis includes:Chapter1, the synthesis, properties and applications of perylenetetracarboxylic diimide derivatives have been reviewed. The research progress of supramolecular aggregates based on Perylenetetracarboxylic Diimides is selected as the focus of this research.Chapter2, three perylenetetracarboxylic diimide (PDI) derivatives comprising a different number of hydrophobic alkoxy chains at one imide nitrogen were synthesized. The aggregation behavior of this series of compounds was investigated by UV-vis absorption and emission spectra. The results indicated that large number of hydrophobic alkyl chains at one end of the PDI molecules can induce significant aggregation in solution, but without obvious ground state interaction between the PDI aromatic cores. The aggregation behavior of this series of compounds in solid state was studied by absorption and IR spectra as well as X-ray diffraction (XRD) experiments. The morphology of the solid aggregates was investigated by scanning electronic microscopy (SEM). With an increase of the number of alkyl chains at one end of these PDI molecules, the aggregation mode varies from H type to J type, while the morphology of the solid aggregates changes from small bending belts to long ordered wires. This research demonstrated that one can control the aggregation mode, the order, and the morphology of the molecular aggregates by changing the number of alkyl chains. This information can be useful in the design of novel organic materials which exhibit molecular aggregation.Chapter3, two new perylenetetracarboxylic diimide (PDI) derivatives, namely dimer1and hexamer2composed of two or six PDI units respectively, are prepared. The aggregation behaviours of these two compounds in solution were investigated by the absorption and fluorescence spectra. The results indicate that hexamer2intend to form large molecular aggregates via intermolecular process even in a much diluted solution. But dimer1prefers to take a folded conformation with the two PDI units stacking in a face-to-face way via an intramolecular process. Infrared spectra revealed the presence of hydrogen bonding between the amide nitrogen and carbonyl oxygen in the molecular aggregates of dimer1and hexamer2. The morphology of the dried gel of dimer1shows bundle of long fibres with very large aspect ratio. But hexamer2presents only small rod-like aggregates with small aspect ratio. This difference is likely caused by the disturbance among different driving forces for the molecular aggregation.Chapter4, a new perylene tetracarboxylic diimide (PDI) trimer1composed of three PDI subunits, which linked at one end with3,4,5-tris(dodecyloxy)benzamide groups has been designed and prepared. The gelating abilities of the trimer in different solvents have been investigated and the results indicated that trimer1can form gel in apolar solvent, such as methyl cyclohexane (MCH). The property of the gel of this trimer has been investigated by UV-vis absorption and emission spectra. The results indicate that the gel of trimer1is composed of typical H aggregates. Temperature-dependent absorption spectra and fluorescence spectra of the diluted gel show that there are almost no changes with the temperature increasing, indicates that the molecular self-assembly in gel is very stable. The structure of dried gel has been investigated by X-ray diffraction (XRD) experiment and the morphology has been measured by atomic force microscopy (AFM). This research revealed that the gel of the trimer formed ordered nano fiber-like structure. This information may be useful for the design of novel organogels based on perylene tetracarboxylic diimides.