Synthesis, Controlled Self-assembly And Properties Of Optical Functional Perylene Diimide

Since Cram and Lehn promulgated the concept of supramolecular chemistry, adjusting the non-covalent interactions between the ions or molecules (such as hydrogen bonding, π-π stacking, hydrophilic-hydrophobic interaction and surface effect) to self-assemble molecules to supramolecular nanomaterials has made miniaturization of device a significant breakthrough. Moreover, the fabrication of smart supramolecular materials that are responsive to external stimuli by the introduction of stimuli-responsive groups into building blocks is believed to have significant potential applications in the field of sensors, molecular circuits, data storage and processing etc.Aiming at the functionality such as sensor, conductivity, storage and conversion etc, we developed perylene diimide derivatives with excellent thermal and photochemical stability, π conjugated rigid plane and the typical n-type semiconductor characteristics as the backbone, and modified with photoresponsive photochromic groups---azobenzene or dithienyl ethylene at the bay position or end position of perylene diimide respectively. Through changing molecular structure by irradiation with specific lignt, we have investigated the dynamics of the molecular self-assembly behavior and its response to light stimulation and realized effective light modulation of its self-assembly process initially. In addition, the applications of nano-supramolecular aggregates and microcrystals as the light-induced conductive switch, fluorescent switch, high conductivity materials have been studied. The detailed research work in this paper is as follows:1. Light-controlled self-assembly and conductance:from nanoribbons to nanospheres based on azobenzene substituted perylene diimidePhotoswitchable azobenzene (AZO) chromophores were introduced to the bay-position of the traditional n-type perylene diimide (PDI). Photocontrolled self-assembly behaviours and the influence of the azobenzene substitution on the assembly structure were investigated by UV/vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). Controlled morphological evolution of the nanostructures from ribbons to spheres was facilely realized by driving the azobenzene switching unit with365nm light irradiation. The nanoribbons demonstrated highly ordered structures while the order of the molecular arrangement was destroyed in the nanospheres, as a result of the curved molecular conformation induced by photoisomerization. In addition, the conductivity of the single nanoribbon was investigated. Thanks to the one-dimensional long-range ordered π-π stacking of the PDI cores, the nanoribbon showed good semiconducting properties with a conductance in the range of2×10-5Sm-1in air. Furthermore, the conductivity decreased with UV light irradiation, mainly due to the increased randomness within the nanostructures, representing the light-induced switching of conductance in the supramolecular systems that is extremely interesting for molecular devices.2. Highly conductive organic single-crystal micro-ribbons formed by a solution process based on azobenzene substituted perylene diimideA novel single-crystal microribbon of Azo-PDIs formed through a solution process as a n-channel semiconductor has been achieved and characterized. Due to the distinctive "H" like close π-π stacking with the shortest vertical contact distance of3.29A, high conductance is determined in the range of0.04-0.5S·m-1. Furthermore, based on the results of conductivity anisotropy, a direct relationship between the maximized conductivity and the optimized molecular stacking is primarily discussed. And it will provide significant guidance on the design of new semiconductor materials with excellent performance.3. Photochromic nanostructures based on diarylethenes with perylene diimideA bisthienylethene-functionalized perylene diimide (BTE-PDI) photochromic dye was synthesized for self-assembly into1-D nanotubes by a reprecipitation method. SEM and TEM observations showed that the nanotubes were formed from their0-D precursors of hollow nanospheres. HR-TEM images revealed that both the nanospheres and the nanotubes have highly ordered lamellar structure, indicating the hierarchical process during assembly. The IR and XRD results revealed that DAE-PDI molecules were connected through intermolecular hydrogen bonds to form building blocks that self-assembled into nanostructures. Electronic absorption and fluorescence spectroscopic results indicated the H-aggregate nature of the self-assembled nanostructures. Competition and cooperation between the dipole-dipole interaction, intermolecular π-π stacking, and hydrophilic/hydrophobic interaction are suggested to result in nanostructures. Reconstruction was found to happen during the morphology transition progress from the0-D nanospheres to the1-D nanotubes, which was driven by donor-acceptor dipole-dipole interactions. Green emission at520nm originating from the DAE subunit was observed for the aggregates of vesicles and nanotubes, which could be regulated by photoirradiation with365nm light, suggesting the nanoaggregates to be photochromic switches.