Synthesis And Self-Assembly Behavior Of Perylene Diimides With Ethylene Glycol Oligomers At Bay Positions

Perylene tetracarboxylic diimide(PDI) derivatives are important molecular building blocks that are currently being investigated for use in a variety of photoactive organic materials. These dyes have generated great interest because of their outstanding photochemical and thermal stability, high luminescence efficiency, wide absorption, desirable optical and optoelectronic properties. They can be applied in organic field-effect transistors, light-harvesting solar cells, photovoltaic devices, light emitting diodes. In the past twenty years, emphasis has been given on the synthesis of tailored functional perylene diimide derivatives by self-assembly leading to one-dimensional stacks of π-π aggregates in solution, especially bay substitution to form amphiphilic perylene diiimides.Ethylene glycol oligomers are a kind of hydrophilic molecules. If the side chain on PDI is completely hydrophobic alkyl long chain, a series of amphiphilic perylene bisimide derivatives can be synthesized through introduction of ethylene glycol oligomers on PDI bay positions. Besides, the unreacted hydroxyl at the end of ethylene glycol oligomers can form hydrogen bonds. So it is worthy of study about the multiple non covalent bonds in amphiphilic molecules and their self-assembly behavior.In this paper, amphiphilic perylene tetracarboxylic diimides with ethylene glycol oligomers at bay positions were designed and a new method, from which the Br at bay position can be substituted by hydroxyl with high efficiency under mild condition, was delevoped to synthesis them. Their self-assembly behavior in solution, and structure and properties of the corresponding self-assembled products were studied. The main results were listed as follows:(1) Dodecylamine substituted at side positions of perylene diimides1,7-H-PDI-C12and Br substituted at bay, dodecylamine substituted at side positions1,7-Br-PDI-C12were synthesized as PTCDA raw material. Comparison between UV-visible and fluorescence spectroscopy, self-assembled morphology and XRD data to analyze π-π interaction difference, the results showed that:Through chloroform/methanol phase transfer, both1,7-Br-PDI-C12and1,7-H-PDI-C12can get red rod nanostructures, and the length of the former is equivalent to seven times than the latter. Under excitation of550-570nm light,1,7-Br-PDI-C12send a strong red fluorescence with certain degree of orientation. But fluorescence intensity of1,7-H-PDI-C12was weaker with low directivity. Since the PDI was substituted by Br at bay positions, which is an electron withdrawing group, the conjugated plane would be distorted and the π-π interaction decreased, leading to increased intermolecular distance from d=3.80A to d=3.94A. Also the stoke shifts were enlarged.(2) Pure triethylene glycol bay substituted perylene diimide1,7-TEG-PDI-C12was synthesized through1,7-Br-PDI-C12substituted with triethylene glycol at Br after several column chromatography and a new method was explored. The conditions of the catalytic system were analyzed through series of reactions and the optimal reaction conditions was ultimately developped, i.e.,18-crown-6ether, K2CO3as the catalyst in THF solvent at room temperature. This method can applied in the reaction between other glycols (monoethylene glycol, hexaethylene glycol, triethylene glycol monomethyl ether) and other perylene diimide derivatives (aniline as side chains) and obtained series glycol oligomers substituted perylenediimides PEG-PDIs. The yields were as high as80%. By means’H-NMR,13C-NMR and other means, all the structures of the compounds were characterized. The results showed that all the molecules had clear structures with high purity.(3) Through concentration, solvent, temperature dependent UV-visible absorption spectra and fluorescence quantum and fluorescence lifetime, the single molecules and aggregated molecules of1,7-TEG-PDI-C12as representation were studies. Through phase transfer the self-assembly product was prepared and its self-assembled morphology, crystal structure were analyzed through microscope (under natural, fluorescent, polarized light), field emission scanning, transmission electron microscope and XRD. The π-π interaction and hydrogen-bond interaction were studied by concentration-dependent1H-NMR Spectroscopy and variable temperature FT-IR spectra. The results showed:the π-π interactions of1,7-TEG-PDI-C12molecules in solution and molecule-solvent interaction were very strong. The well-ordered self-assembled pruducts occured under the two interactions with spectra peaks change, A0-1/A0-0ratio increase and fluorescence quantum lifetime reduction.1,7-TEG-PDI-C12in hexanol solvent were easier to form J-aggregates under the interaction of π-π and hydrogen bonding. The self-assembly products losed fluorescence and direction gradually and formed a black cylindrical "Cordyceps" crystal structure through slow phase transfer in THF/water co-solvent, since the hydrophobic dodecyl chain, hydrophilic glycol chain and hydroxyl hydrogen bonding interactions. The molecular plied in the direction of the π-π stacking interaction with stacking distance of about3.49A.1,7-TEG-PDI-C12self-assemblied into different nanostructures at different concentrations of THF/water co-solvent diffusion quickly, including nanowires, nanoparticles, and nanospheres.(4) The effect of molecular structure on perylene diimides photophysical properties and self-assembly behavior were studied through concentration-dependent UV-visible absorption and fluorescence spectroscopy, temperature UV-visible absorption spectroscopy, and electron microscopy. The results showed that1,7-SEG-PDI-C12,1-Br-7-MEG-PDI-C12,1,7-TEGOCH3-PDI-C12tended to form J-aggregates and the aggregation behavior of1,7-TEG-PDI-Ph was different. After spreading in THF/water co-solvent quickly, each perylene diimide solution self-assembled into different structures.1,7-SEG-PDI-C12mainly formed nanoparticles due to the strong π-π interaction, hydrogen bonding and hydrophilic/hydrophobic interaction;1-Br-7-MEG-PDI-C12mainly formed nanosheet for weaker hydrophilic/hydrophobic force;1,7-TEGOCH3-PDI-C12formed droplets by π-π and hydrophilic/hydrophobic interaction with less order;1,7-TEG-PDI-Ph self-assemble into nano-needles due to increased conjugate plane.